CIE 115-2010_Road Lighting

ISBN 978 3 901906 86 2

LIGHTING OF ROADS FOR MOTOR AND PEDESTRIAN TRAFFIC

CIE 115:2010 2nd Edition UDC:

628.971 628.971.6

Descriptor: Exterior lighting Street lighting (fixed)

THE INTERNATIONAL COMMISSION ON ILLUMINATION The International Commission on Illumination (CIE) is an organisation devoted to international co-operation and exchange of information among its member countries on all matters relating to the art and science of lighting. Its membership consists of the National Committees in about 40 countries. The objectives of the CIE are: 1. To provide an international forum for the discussion of all matters relating to the science, technology and art in the fields of light and lighting and for the interchange of information in these fields between countries. 2. To develop basic standards and procedures of metrology in the fields of light and lighting. 3. To provide guidance in the application of principles and procedures in the development of international and national standards in the fields of light and lighting. 4. To prepare and publish standards, reports and other publications concerned with all matters relating to the science, technology and art in the fields of light and lighting. 5. To maintain liaison and technical interaction with other international organisations concerned with matters related to the science, technology, standardisation and art in the fields of light and lighting. The work of the CIE is carried on by seven Divisions each with about 20 Technical Committees. This work covers subjects ranging from fundamental matters to all types of lighting applications. The standards and technical reports developed by these international Divisions of the CIE are accepted throughout the world. A plenary session is held every four years at which the work of the Divisions and Technical Committees is reviewed, reported and plans are made for the future. The CIE is recognised as the authority on all aspects of light and lighting. As such it occupies an important position among international organisations. LA COMMISSION INTERNATIONALE DE L'ECLAIRAGE La Commission Internationale de l'Eclairage (CIE) est une organisation qui se donne pour but la coopération internationale et l'échange d'informations entre les Pays membres sur toutes les questions relatives à l'art et à la science de l'éclairage. Elle est composée de Comités Nationaux représentant environ 40 pays. Les objectifs de la CIE sont : 1. De constituer un centre d'étude international pour toute matière relevant de la science, de la technologie et de l'art de la lumière et de l'éclairage et pour l'échange entre pays d'informations dans ces domaines. 2. D'élaborer des normes et des méthodes de base pour la métrologie dans les domaines de la lumière et de l'éclairage. 3. De donner des directives pour l'application des principes et des méthodes d'élaboration de normes internationales et nationales dans les domaines de la lumière et de l'éclairage. 4. De préparer et publier des normes, rapports et autres textes, concernant toutes matières relatives à la science, la technologie et l'art dans les domaines de la lumière et de l'éclairage. 5. De maintenir une liaison et une collaboration technique avec les autres organisations internationales concernées par des sujets relatifs à la science, la technologie, la normalisation et l'art dans les domaines de la lumière et de l'éclairage. Les travaux de la CIE sont effectués par 7 Divisions, ayant chacune environ 20 Comités Techniques. Les sujets d'études s'étendent des questions fondamentales, à tous les types d'applications de l'éclairage. Les normes et les rapports techniques élaborés par ces Divisions Internationales de la CIE sont reconnus dans le monde entier. Tous les quatre ans, une Session plénière passe en revue le travail des Divisions et des Comités Techniques, en fait rapport et établit les projets de travaux pour l'avenir. La CIE est reconnue comme la plus haute autorité en ce qui concerne tous les aspects de la lumière et de l'éclairage. Elle occupe comme telle une position importante parmi les organisations internationales. DIE INTERNATIONALE BELEUCHTUNGSKOMMISSION Die Internationale Beleuchtungskommission (CIE) ist eine Organisation, die sich der internationalen Zusammenarbeit und dem Austausch von Informationen zwischen ihren Mitgliedsländern bezüglich der Kunst und Wissenschaft der Lichttechnik widmet. Die Mitgliedschaft besteht aus den Nationalen Komitees in rund 40 Ländern. Die Ziele der CIE sind : 1. Ein internationaler Mittelpunkt für Diskussionen aller Fragen auf dem Gebiet der Wissenschaft, Technik und Kunst der Lichttechnik und für den Informationsaustausch auf diesen Gebieten zwischen den einzelnen Ländern zu sein. 2. Grundnormen und Verfahren der Messtechnik auf dem Gebiet der Lichttechnik zu entwickeln. 3. Richtlinien für die Anwendung von Prinzipien und Vorgängen in der Entwicklung internationaler und nationaler Normen auf dem Gebiet der Lichttechnik zu erstellen. 4. Normen, Berichte und andere Publikationen zu erstellen und zu veröffentlichen, die alle Fragen auf dem Gebiet der Wissenschaft, Technik und Kunst der Lichttechnik betreffen. 5. Liaison und technische Zusammenarbeit mit anderen internationalen Organisationen zu unterhalten, die mit Fragen der Wissenschaft, Technik, Normung und Kunst auf dem Gebiet der Lichttechnik zu tun haben. Die Arbeit der CIE wird in 7 Divisionen, jede mit etwa 20 Technischen Komitees, geleistet. Diese Arbeit betrifft Gebiete mit grundlegendem Inhalt bis zu allen Arten der Lichtanwendung. Die Normen und Technischen Berichte, die von diesen international zusammengesetzten Divisionen ausgearbeitet werden, sind auf der ganzen Welt anerkannt. Alle vier Jahre findet eine Session statt, in der die Arbeiten der Divisionen überprüft, berichtet und neue Pläne für die Zukunft ausgearbeitet werden. Die CIE wird als höchste Autorität für alle Aspekte des Lichtes und der Beleuchtung angesehen. Auf diese Weise unterhält sie eine bedeutende Stellung unter den internationalen Organisationen. Published by the COMMISSION INTERNATIONALE DE L'ECLAIRAGE CIE Central Bureau Kegelgasse 27, A-1030 Vienna, AUSTRIA Tel: +43(1)714 31 87 0, Fax: +43(1)714 31 87 18 e-mail: [email protected] WWW: http://www.cie.co.at/ © CIE 2010 - All rights reserved

ISBN 978 3 901906 86 2

LIGHTING OF ROADS FOR MOTOR AND PEDESTRIAN TRAFFIC

CIE 115:2010 2nd Edition UDC:

628.971 628.971.6

Descriptor: Exterior lighting Street lighting (fixed)

CIE 115:2010

This Technical Report has been prepared by CIE Technical Committee 4-44 of Division 4 "Lighting and Signalling for Transport" and has been approved by the Board of Administration of the Commission Internationale de l'Eclairage for study and application. The document reports on current knowledge and experience within the specific field of light and lighting described, and is intended to be used by the CIE membership and other interested parties. It should be noted, however, that the status of this document is advisory and not mandatory. The latest CIE proceedings or CIE NEWS should be consulted regarding possible subsequent amendments. Ce rapport technique a été élaboré par le Comité Technique CIE 4-44 de la Division 4 "Eclairage et signalisation pour les transports" et a été approuvé par le Bureau de la Commission Internationale de l'Eclairage, pour étude et emploi. Le document expose les connaissances et l'expérience actuelles dans le domaine particulier de la lumière et de l'éclairage décrit ici. Il est destiné à être utilisé par les membres de la CIE et par tous les intéressés. Il faut cependant noter que ce document est indicatif et non obligatoire. Il faut consulter les plus récents comptes rendus de la CIE, ou le CIE NEWS, en ce qui concerne des amendements nouveaux éventuels. Dieser Technische Bericht ist vom Technischen Komitee CIE 4-44 der Division 4 "Beleuchtung und Signale für den Verkehr" ausgearbeitet und vom Vorstand der Commission Internationale de l'Eclairage gebilligt worden. Das Dokument berichtet über den derzeitigen Stand des Wissens und Erfahrung in dem behandelten Gebiet von Licht und Beleuchtung; es ist zur Verwendung durch CIE-Mitglieder und durch andere Interessierte bestimmt. Es sollte jedoch beachtet werden, dass das Dokument eine Empfehlung und keine Vorschrift ist. Die neuesten CIE-Tagungsberichte oder die CIE NEWS sollten im Hinblick auf mögliche spätere Änderungen zu Rate gezogen werden. Any mention of organisations or products does not imply endorsement by the CIE. Whilst every care has been taken in the compilation of any lists, up to the time of going to press, these may not be comprehensive. Toute mention d'organisme ou de produit n'implique pas une préférence de la CIE. Malgré le soin apporté à la compilation de tous les documents jusqu'à la mise sous presse, ce travail ne saurait être exhaustif. Die Erwähnung von Organisationen oder Erzeugnissen bedeutet keine Billigung durch die CIE. Obgleich große Sorgfalt bei der Erstellung von Verzeichnissen bis zum Zeitpunkt der Drucklegung angewendet wurde, besteht die Möglichkeit, dass diese nicht vollständig sind.

© CIE 2010 - All rights reserved

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CIE 115:2010

The following members of TC 4-44, "Management and Maintenance of Road Lighting", took part in the preparation of this Technical Report. The committee comes under Division 4 "Lighting and Signalling for Transport". Members: T. Adams

Netherlands

A. Augdal

Norway

M. Bizjak

Slovenia

E. Bjelland

Norway (secretary)

N. Bonne

Netherlands

C. Chain

France

M. Gillet

Belgium

B. Hamel

Netherlands

P. Hautala

Finland (chairman)

J. Kotek

Czech Republic

T. Kristoffersen

Norway

P. Lutkevich

USA

T. Mjøs

Norway (co-secretary)

S. Onaygil

Turkey

J.L. Pimenta

Brazil

G. Rossi

Italy

R. Stark

USA

B. Shortreed

United Kingdom

D. Simpson

United Kingdom

A. Stockmar

Germany

M. van den Bosch

Belgium

T. van den Brink

Netherlands

A. van den Broek

Netherlands

P.O. Wanvik

Norway

H.-C. Zhang

People’s Republic of China

C. Andersen

USA

P.J. Larsen

Norway

S. Takashi

Japan

Advisors:

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CONTENTS SUMMARY

VI

RESUME

VI

ZUSAMMENFASSUNG

VI

1 INTRODUCTION 1.1 General 1.2 Need for Road Lighting

1 1 1

2 TERMS AND DEFINITIONS 2.1 Average Luminance of the Road Surface [Lav] 2.2 Overall Uniformity of Road Luminance [Uo] 2.3 Longitudinal Uniformity of Road Surface Luminance [Ul] 2.4 Threshold Increment TI [fTI] 2.5 Surround Ratio SR [Rs] 2.6 Discomfort Glare

2 2 2 2 3 3 3

3 THE PURPOSE OF ROAD LIGHTING

3

4 ROAD LIGHTING FOR THE MOTORIST 4.1 General Information 4.2 The Role of Road Lighting in Motor Traffic Safety

4 4 4

5 VISUAL CONDITIONS CONFRONTING THE MOTORIST 5.1 General 5.2 Urban Conditions 5.3 Rural Conditions 5.4 Weather Conditions 5.5 Age of the Road User 5.6 The Driver's Task and Visual Requirements 5.7 Direct Visual Guidance

4 4 4 5 5 5 6 7

6 QUALITY CRITERIA AND LIGHTING CLASSES 6.1 Quality Criteria for Road Lighting 6.2 Selection of Lighting Classes 6.2.1 Normal Lighting 6.2.2 Adaptive Lighting

7 7 7 7 8

7 REQUIREMENTS FOR MOTORIZED TRAFFIC 7.1 The Luminance Concept 7.2 Practical Considerations for Direct Visual Guidance

9 9 12

8 THE LIGHTING OF CONFLICT AREAS

12

9 ROAD LIGHTING FOR PEDESTRIANS 9.1 General 9.2 Crime and Lighting Studies 9.3 Road Accidents in Residential Areas 9.4 Quality Criteria 9.4.1 Lighting of Horizontal Surfaces 9.4.2 Lighting of Vertical Surfaces 9.4.3 Control of Glare 9.4.4 Choice of Light Source 9.5 Lighting Levels for Pedestrian and Low Speed Traffic Areas

15 15 16 16 16 16 16 17 17 17

10 APPEARANCE AND ENVIRONMENTAL ASPECTS 10.1 Energy Conservation 10.2 Appearance 10.3 Obtrusive Light

19 19 19 20

11 VISIBILITY CONCEPT AND MESOPIC VISION

20

12 REFERENCES

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ANNEX A: EXAMPLE OF ECONOMIC CALCULATIONS A.1 Costs A.2 Profitability of Road Lighting A.3 Examples

23 23 25 26

ANNEX B: ROAD LIGHTING UNDER SNOW CONDITIONS

28

ANNEX C: THRESHOLD INCREMENT TI [FTI]

29

ANNEX D: CONTROL OF GLARE IN PEDESTRIAN AND LOW SPEED TRAFFIC AREAS 30 ANNEX E: EXAMPLES FOR M, C, AND P LIGHTING CLASSES

32

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LIGHTING OF ROADS FOR MOTOR AND PEDESTRIAN TRAFFIC SUMMARY This report is a revision and update of CIE 115-1995 Recommendations for the Lighting of Roads for Motor and Pedestrian Traffic. Since it was issued in 1995 power consumption and environmental aspects have become more important and at the same time, the improved performance of luminaires and lamps, and especially the introduction of electronic control gear, has made it possible to introduce adaptive lighting for roads for motorised traffic, conflict areas and areas for pedestrians. A structured model has been developed for the selection of the appropriate lighting classes (M, C, or P), based on the luminance or illuminance concept, taking into account the different parameters relevant for the given visual tasks. Applying for example time dependent variables like traffic volume or weather conditions, the model offers the possibility to use adaptive lighting systems.

L'ECLAIRAGE DES ROUTES POUR LES VEHICULES A MOTEUR ET LES PIETONS RESUME Ce rapport a pour objet la mise à jour du rapport technique CIE 115-1995 Recommendation for the Lighting of Roads for Motor and Pedestrian Traffic. Depuis sa publication en 1995, les consommations énergétiques et les aspects environnementaux sont devenus des enjeux plus importants. Par ailleurs, l'amélioration des performances des luminaires et des sources d'éclairage, et en particulier l'introduction des systèmes électroniques de contrôle des installations, a permis d'introduire la pratique de variation de l'éclairage des routes, des zones de conflit et des espaces piétons. Un modèle structuré permettant la sélection des classes d'éclairage (M, C ou P) a été développé ; il est basé soit sur le concept de luminances, soit sur celui de niveaux d'éclairement, et prend en compte les différents paramètres pertinents pour caractériser la tâche visuelle. En considérant des variables temporelles telles que le trafic ou les conditions climatiques, le modèle répond aux utilisations des systèmes de variation d'éclairage.

BELEUCHTUNG VON STRASSEN FÜR FUSSGÄNGER UND MOTORISIERTEN VERKEHR ZUSAMMENFASSUNG Dieser Bericht ist mit dem Ziel erarbeitet worden, die Publikation CIE 115-1995 Recommendation for the Lighting of Roads for Motor and Pedestrian Traffic auf den neuesten Stand zu bringen. Seit ihrer Herausgabe im Jahr 1995 sind Aspekte des Energieverbrauchs und des Umweltschutzes verstärkt in den Vordergrund getreten. Gleichzeitig ist es durch den Einsatz leistungsfähigerer Lampen und Leuchten und besonders durch die Verfügbarkeit elektronischer Betriebsgeräte möglich geworden, adaptive Beleuchtungen für Straßen, Konfliktzonen und Fußgängerbereiche einzuführen. Es wird ein neu entwickeltes, vereinfachtes Verfahren zur Auswahl geeigneter Beleuchtungsklassen (M, C oder P) vorgestellt, aufbauend auf dem Beleuchtungsstärke- oder Leuchtdichte-Konzept, unter Berücksichtigung der verschiedenen, für die gegebenen Sehaufgaben relevanten Parameter. Bei Anwendung zum Beispiel Zeit abhängiger Variablen wie Verkehrsaufkommen oder Wetterbedingungen eröffnet das Modell die Möglichkeit, adaptive Beleuchtungssysteme einzusetzen.

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1 INTRODUCTION 1.1 General The recommendations in this Technical Report are structured with the intention of making them easily adaptable to the needs of individual countries. This document is a framework, which could serve for developing national codes of practice and standards. Since Publication CIE 115-1995, Recommendations for the Lighting of Roads for Motor and Pedestrian Traffic, was issued, the performance of luminaires and lamps has improved and the realization of efficient adaptive lighting systems is technically possible at reasonable cost. This technical report considers these matters in detail and gives information about the use of control systems able to satisfy the requirements of adaptive lighting. The visibility level concept and Small Target Visibility (STV) algorithm are not considered here because they are under evaluation in CIE TC 4-36 “Visibility Design for Roadway Lighting”. The report is based on experience gained worldwide in the application of the luminance concept to the lighting of traffic routes. The document takes into account the needs of all road users. In conformity with the most recent CIE practice, this report is based on maintained lighting levels (CIE 154:2003) and lighting quality. This implies that performance must not fall below the prescribed limits, which are minimum values, for the life of the installation. 1.2 Need for Road Lighting The decision on whether a road should be lit is defined in the national road lighting policy. This varies by country or municipality. Specific guidelines are usually available at national level for each country. Matters that need to be considered when planning and installing road lighting are summarized below: a) When the service level of traffic conditions and standard of the road are normal the need for road lighting will usually be evaluated on the basis of traffic volume and traffic speed. b) It is possible to estimate the savings in road usage costs that can be attained through the benefits of road lighting. The most important savings are through the reduction in accident rates and severity. In accordance with Publication CIE 931992, Road Lighting as an Accident Countermeasure, road lighting will decrease night-time accidents on average 30 %. Calculations must always be based on the national values of reduction of night-time accident rates, see Annex A, examples 7 and 8. c) The basis for calculating the benefits of those road lighting installations that are justified by traffic volume is the average personal injury and fatality rate for each road class. On motorways and other highways, the savings obtained in travel time are also considered. d) The profitability of road lighting in terms of traffic economy is analyzed by comparing the average annual savings in total costs of road traffic with the annualized total costs of the lighting system and the annual cost of collisions with installed lighting columns. The traffic volume required to make road lighting profitable is obtained by performing the analysis for the period from installation to half of the anticipated service life of the road lighting system. An example of a calculation method is provided in Annex A. e) Where traffic volumes are lower than those needed to justify lighting on accident reduction grounds alone, road lighting may be justified if there is an inhomogeneous traffic environment, poor road alignment, short spacing of junctions, greater than normal number of crossroads and bus stops, a lack of dedicated pedestrian footways, etc.

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CIE 115:2010

f)

On some types of roads, particularly in urban areas and on residential roads, injury and fatal accidents may not be relevant, and the benefits of lighting cannot be evaluated only in terms of the potential reduction in injury accident rates. On such roads, lighting is provided for social reasons; to improve the general amenity, to give safe passage for pedestrians and to provide a sense of personal security (see clause 9)

The methods presented in clauses 7, 8 and 9 have to be considered as the starting points of a comprehensive approach. In that sense, the models cannot cover all the different road cases; they introduce general parameters and the impact on lighting requirements. Only the real situation and its unique characteristics (geometry of the road, marking, visual environment, difficulty of the navigation task, lack of visibility, risks of glares due to existing elements, local weather, specific users such as high rate of elderly or visually impaired people, etc.) can lead to a final determination of luminous requirements. Renewal or refurbishment of obsolete and uneconomic installations is important. It is possible to obtain higher luminance values with lower energy consumption using new designs and new technology. The upgrading of lighting and control systems will often give good costbenefit ratios and short amortization periods. The visual needs of road users under reduced traffic volumes during certain periods of night or under varying weather conditions, and the positive benefits of reduced energy consumption and potential environmental improvements, are some of the considerations which justify the installation of adaptive road lighting. There are a variety of suitable instruments, devices and methods which can be used for the intelligent control of a road lighting installation. The control systems range from very simple to the most sophisticated applications. 2 TERMS AND DEFINITIONS The terms discussed in this clause are defined in the International Lighting Vocabulary (CIE DS 017.2/E:2009) or in CIE 140-2000. 2.1 Average Luminance of the Road Surface [Lav] The values of Lav are the minimum values to be maintained throughout the life of the installation for the specified lighting class(es). They are dependent on the light distribution of the luminaires, the luminous flux of the lamps, the geometry of the installation, and on the reflection properties of the road surface. Higher levels are acceptable when they can be environmentally or economically justified. The calculation of the average luminance of the road surface should be carried out in accordance with CIE 140-2000. Calculated values should consider the luminaire and lamp maintenance factors. Luminaire maintenance factors vary according to the intervals between cleaning, the amount of atmospheric pollution, the quality of the sealing of the lamp housing of the luminaire, and the age of the materials. Their values may be established by field measurements. Lamp flux maintenance factors vary according to lamp type and power. Values are usually available from lamp manufacturers. 2.2 Overall Uniformity of Road Luminance [Uo]

Uo is the ratio of the minimum luminance at a point to the average road surface luminance and should be calculated according to CIE 140-2000. This criterion is important as regards the control of minimum visibility on the road. 2.3 Longitudinal Uniformity of Road Surface Luminance [Ul]

Ul is the ratio of the minimum to the maximum luminance along a line or lines parallel to the run of the road and should be calculated in accordance with CIE 140-2000. It is mainly a criterion relating to comfort and its purpose is to prevent the repeated pattern of high and low

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CIE 115:2010

luminance values on a lit run of road becoming too pronounced. It only applies to long uninterrupted sections of road. 2.4 Threshold Increment TI [fTI] Disability glare results from the scattering of light within the eye, so reducing contrasts of the retinal image. The effect may be explained by the superimposition of a uniform luminance veil over the scene, which is quantified as the equivalent veiling luminance. The magnitude of this depends on the illuminance on the driver's eye from the luminaires and the angles at which they are seen. While the degree of disability glare increases with the equivalent veiling luminance, it decreases as a function of the average road luminance. TI is a measure of the loss of visibility caused by the disability glare from the road lighting luminaires. The formula from which it is calculated is based on the percentage increase in the luminance difference needed to make the object visible in the presence of glare when it is just visible in the absence of glare, that is, when the luminaires are screened from the view of the observer. The mathematical procedure is given in CIE 140-2000, (see Annex C of this report for additional remarks) and the calculation is made for a clean luminaire equipped with a lamp emitting the initial luminous flux. 2.5 Surround Ratio SR [Rs] One of the principal aims in road lighting is to create a bright road surface against which objects can be seen. However, the upper parts of tall objects on the road and objects towards the side of the road, particularly on curved sections, are seen against the surrounds of the road. Thus adequate lighting on the surrounds helps the motorist to perceive more of the environment and make speed adjustments in time. The function of the surround ratio is to ensure that light directed on the surrounds is sufficient for objects to be revealed. In situations where lighting is already provided on the surrounds the use of surround ratio is rendered unnecessary. Surround ratio is defined in CIE 140-2000. 2.6 Discomfort Glare No fully satisfactory method has yet been devised for quantifying discomfort glare to drivers on traffic routes. Formerly G, the Glare Control Mark (CIE 31-1976), was used but resulted in anomalies. Field evidence suggests that installations designed within the limits of threshold increment recommended in Tables 2 and 5 are generally acceptable as regards discomfort glare. Bright surroundings, such as lighted buildings, tend to mitigate discomfort glare but as the lighting of buildings is variable and may be extinguished during the night, it is not practicable to allow for this in the design of the road lighting. 3 THE PURPOSE OF ROAD LIGHTING There are three main purposes of road lighting: 1) to allow all road users, including operators of motor vehicles, motor cycles, pedal cycles, and animal drawn vehicles to proceed safely, 2) to allow pedestrians to see hazards, orientate themselves, recognize other pedestrians, and give them a sense of security, 3) to improve the day-time and night-time appearance of the environment. In the lighting of roads and other public routes the relative importance of these items needs to be evaluated, particularly as regards the first two, since the needs of motorists and pedestrians differ. The last item, which is the amenity aspect, is important to all road users and residents, both in day-time and in night time.

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4 ROAD LIGHTING FOR THE MOTORIST 4.1 General Information Road traffic continues to grow in volume as technological gains and emerging societies place greater reliance on road transportation. While most of this traffic proceeds during daylight hours there is a considerable volume of traffic during periods of darkness. In some countries an average of about 25 % of travel occurs during night-time hours. Fatal road accident rates during darkness, however, are approximately three times greater than those during daylight, mainly due to reduced visibility during this period (CIE 180:2007). Headlights provide some of the visual cues required at night, but become progressively ineffective as speed, number of vehicles, or complexity of the night-time scene increases. Moreover, they are glaring to oncoming traffic, especially where no road lighting is installed. This problem is further aggravated on two-way roads where vehicles travelling in opposite directions are in close proximity. Mitigation of headlight glare is accomplished by good quality road lighting, which improves comfort and provides the motorist with the ability to see details clearly and locate them in sufficient time to react effectively. The criteria and specific values for good quality road lighting are provided in this report. The recommendations given are based on research and experience in all aspects of the visual requirements at night. They include the physiology of the visual system, human factors (psychological) related to driver performance and the statistical evaluation of actual installations. There is ample evidence that good quality road lighting increases safety (CIE 93-1992). 4.2 The Role of Road Lighting in Motor Traffic Safety The purpose of road lighting is to provide visual cues and reveal obstacles, so that safe vehicular operation is possible. While headlights and other traffic safety devices (road surface markings, delineators, signs, etc.) are of assistance in providing the motorist with guidance, there is a need to reveal extraneous objects that suddenly appear on the road. The distance required to bring a vehicle to a stop safely can exceed the distance at which headlights can adequately reveal the object, depending on recognition, reaction and braking times, and factors such as the speed of the vehicle and whether the road surface is wet or dry. Good quality road lighting can provide the visibility required at this distance, so that evasive action can be taken in good time, without resort to an abrupt manoeuvre. Fixed road lighting with its usual overhead sources, provides illumination on the road and its surrounds thereby opening up the field of view to something more approaching daylight conditions. This factor is primarily of importance in areas of high visual complexity, where there may be different types of road user (such as motorists, cyclists, pedestrians, and slow moving farm equipment) present at the same time. It is also of importance where there are sharp bends in the road. Many studies of after-dark accident rates confirm that these can be reduced by 20 % to 30 % when unlit accident prone areas are lit with good quality lighting. The prediction of accident rate changes as a result of changes in the standard of road lighting is not well established and is still the subject of investigation. 5 VISUAL CONDITIONS CONFRONTING THE MOTORIST 5.1 General The visual field of the driver consists of the carriageway, the surrounds on each side, the visible landscape, and the sky. Any object, about which information is necessary, must be clearly displayed against that part of the field which forms the immediate background. 5.2 Urban Conditions Pedestrians are an important part of the scene. They are present on most types of traffic route and are observed against various backgrounds, such as the road, surrounding buildings, or open areas, which may or may not be lighted. Where the background is light the pedestrian tends to be seen in negative contrast (silhouette), although some features may be 4

CIE 115:2010

apparent. Similarly, the pedestrian may be seen in positive contrast when the background is dark. Surround luminance, which, in urban areas, may be comparable to that of the road surface, can reduce the effect of discomfort glare, and requirements for glare control of the road lighting luminaires may be less restrictive in these areas. 5.3 Rural Conditions Rural areas are generally devoid of illuminated backgrounds, which are helpful in reducing discomfort glare. Road lighting luminaires in these situations require more stringent control of the light intensity distribution at angles at which they may be viewed. Driving on these roads is usually more difficult because of the variety of problems which may be encountered; traffic is mixed and may include pedestrians, all kind of cyclists offering a wide range of speed, and non-motorized equipment. 5.4 Weather Conditions The lighting requirements for motorized traffic can be most easily fulfilled under dry conditions. Where appropriate, the design should take wet road conditions into consideration. Under wet conditions the road luminance becomes less uniform. Poor uniformity leads to increased susceptibility to glare as well as the production of glare from the shiny surface reflections of wet areas, as the road surface tends to behave in a more specular way, rather than as a diffuse reflector. The brighter parts of the road diminish in area and increase in luminance, and the converse is true for the darker areas. The result is that in wet conditions the average luminance in most cases increases whereas the uniformity of the luminance is severely degraded. The visibility on a large proportion of the road is adversely affected. The possible increase of the average luminance should not be used as a justification for dimming the lighting system. Additional lighting requirements are needed to ameliorate these effects in those regions where the road surface is wet for a considerable proportion of the total time. In such regions a light distribution should be selected which minimizes this harmful effect (CIE 47-1979 gives details for calculating Uo for wet conditions). In addition, consideration should be given, wherever possible, to the selection of pervious materials for the road surface, which can also be beneficial. When the road is snow covered, the road luminance levels tend to be higher than typical design levels. The levels may be as high as 4 to 5 times the required level, depending on the condition of the snow and of the average luminance coefficient q0 used for the road surface in the design for dry conditions. This provides a possibility for dimming the installation, but not for switching off. Reducing the power output from every lamp by the same amount will not affect luminance uniformity or the object contrast. Reduction by switching off individual luminaires, however, will not meet the requirements for the selected lighting class. (See Annex B, for further explanations) Fog obscures the visual field to a degree depending on its density. On motorways, where high speeds prevail, this can give rise to dangerous situations, particularly if the fog is patchy. Good lighting can provide information on the immediate surrounds and give visual guidance (see 5.7) as to the direction of the road, particularly in light fog, but could also encourage drivers to proceed at higher speeds than they would otherwise. 5.5 Age of the Road User Visual capability decreases with age. This occurs as the result of three effects. Firstly, the transmission of the ocular media decreases with age; for instance at the age of 70 it is only 28 % of that of a 25 year old person. Secondly, light scattering in the ocular media increases with age, which reduces the apparent contrast of objects so that, for instance, for a 70 year old person there is on average 2,2 times more scattered light, expressed as the equivalent veiling luminance, than for a 25 year old person. As a result of these first two effects a higher contrast threshold is required for the perception of targets by the older person. Thus, a 70 year old observer requires about three times more contrast at the threshold of visibility than a 25 year old observer. Thirdly, the receptor density in the retina decreases with age thus reducing the ability of the eye to resolve detail even if the eye is optically corrected. Thus

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a 70 year old observer has on the average a visual acuity of only 66 % of that of a 25 year old (Le Grand, 1957). Older people are also more susceptible to glare. There is still a need for more research on this issue, but some information can be found in Annex C. NOTE In locations with a high proportion of older people, such as around old people’s homes or some hospitals, consideration can be given to providing a higher lighting class than that indicated by the selection process, and/or using light sources with a good colour rendering index. 5.6 The Driver's Task and Visual Requirements There are three levels in the driving task (CIE 100-1992): 1) Positional level - routine steering or speed adjustment necessary to maintain a desired speed and to remain within the carriageway. 2) Situational level - change in speed, direction of travel, position on the road, required as a result of a change in the geometric, operational, or environmental situation. 3) Navigational level - selecting and following a route from the origin to the destination of a trip. During normal driving all three are performed simultaneously. As the complexity of the driving task increases, there is a tendency to ignore the higher levels (level 3 then level 2) in order to concentrate on the lower level orders. Each of the above levels requires particular kinds of visual information to allow the driving task to be performed properly. The positional level requires visual information on such items as carriageway markers (retro-reflective markers or active markers) on lined roads, edge lines, and kerbs. These must be seen in sufficient time to maintain safely the vehicle's velocity and position. This visual guidance is provided by adequate luminance levels and luminance uniformity. Where visual guidance only is required, it can be provided with the lamps operating at reduced power outputs below the levels needed to provide normal or adaptive lighting levels. The importance of guidance increases with decreasing traffic volume. The situational level requires visual information on the relative position, speed and changes in speed of surrounding vehicles, other objects on the road, road markings, and any other visual guidance, so that manoeuvres such as following, overtaking and stopping can safely be accomplished. The importance of this level increases with increasing traffic volume. The ability to manoeuvre safely requires that objects be perceptible in time for the driver to act comfortably. The visibility of objects is related to the level and distribution of the road surface luminance. The average road surface luminance largely determines the adaptation level of the eye; in general the higher the adaptation level caused by the background luminance level the more sensitive the eye is to contrast and the better the visual performance. The road surface is the most important part of the background and it follows that its luminance rather than its illuminance determines adaptation level. Because of this, road luminance is an important quality criterion. The illuminance on vertical planes transverse or parallel to the axis of the road, however, may under certain conditions comprise a useful addition to luminance data. The uniformity of the road luminance is important for providing a background against which objects, or small parts of objects, can be observed. The navigational level, in addition to pre-trip planning, must include visual information on landmarks, the environment, intersections, guide signs, and other formal information sources. The navigational level requires that the run of the road surfaces be obvious, especially at intersections, bifurcations, and interchanges. Road markings, such as arrows and instructional information as well as other symbols must be seen in advance for proper navigational movements. The level of the road luminance should be high and uniform enough to contribute to this visual process.

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Good visual conditions must prevail over the entire road scene to enable the various levels of the driving task to be executed safely. Ease of perception can result in better driving comfort, expressed in less strain and stress on the motorist. It can improve the ability to deal with unexpected traffic, geometrical, or environmental events. When either a flat or a three-dimensional object is seen against the road surface as a background, then the contrast between the object and the background can be influenced by the geometry of the location of the luminaires and by their light distribution. Contrast reversals may occur; to minimize these effects evaluation should be made using a visibility model such as that described by Adrian (Adrian, 1989). At the moment, it is not possible to suggest a specific model. These aspects are under evaluation in CIE TC 4-36 “Visibility Design for Roadway Lighting”. 5.7 Direct Visual Guidance Direct light from the luminaires can aid the motorist when they delineate the road ahead. This may be particularly significant on winding roads and at complex junctions and can be a most useful contribution of lighting systems. 6 QUALITY CRITERIA AND LIGHTING CLASSES 6.1 Quality Criteria for Road Lighting The approach generally used when selecting quality criteria for lighting roads for motor traffic is based on the luminance concept. Illuminance is still used by some countries, but experience has shown this to be an unsatisfactory criterion. In the application of the luminance concept, the aim is to provide a bright road surface against which objects are seen in silhouette. It uses, therefore, level and uniformity of road surface luminance, as well as glare control, as quality criteria. However, many objects on the road are of high reflectance, so they are not seen in silhouette but rather by directly reflected light. Furthermore, in congested traffic conditions, much of the view of the road surface may be obstructed by vehicles and thus cannot provide a background for revealing objects. Nevertheless, the approach of providing a good level and uniformity of road luminance with adequate glare control has been widely adopted in national and international recommendations. Experience gained in using these criteria for a number of decades indicates that they provide a satisfactory basis for road lighting design. Although prescribed values of the criteria were originally arrived at as a result of experimental work, they have been tempered by experience over this time and the approach suggested in this document represents good present-day practice. However, in special situations called "conflict areas" in this report, the design of the lighting installation can be based on the illuminance concept, as described in clause 8. The lighting design for pedestrian and very low speed areas is also based on illuminance requirements as described in clause 9. 6.2 Selection of Lighting Classes Tables quantifying the details of different lighting classes and referred to below can be found in the relevant clauses following, where they are discussed in more detail. 6.2.1 Normal Lighting Normal lighting class is that class which is appropriate if the same level is to be used throughout the hours of darkness, selected from Table 2, 5 or 7. In selecting the normal lighting class the maximum value of the selection parameters likely to occur at any period of operation should be considered, e.g. for traffic volume consider peak hourly value. The installation should be designed to comply with all the quantitative and qualitative requirements of the selected class. Many countries have developed valid systems to determine the appropriate normal lighting class (CEN, 2004, CERTU, 2008, BS, 2003, UNI, 2007). A system which can be used to determine the normal lighting class for motor traffic, conflict areas and road lighting for pedestrians is given in Clauses 7, 8 and 9 using Tables 1, 3 and 6 respectively.

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For simplicity only the most important parameters are summarized in Table 1 for ordinary motorized traffic, Table 3 for conflict areas and Table 6 for pedestrian and low speed areas. The descriptions of the parameters and the associated options are broad so that they can be interpreted to suit individual requirements for national recommendations. In some cases risk analysis or other consideration (environmental for example) could lead to the consideration of other parameters. When a selection is made, all road users, including motorists, motor and pedal cyclists, and pedestrians should be considered. Examples of the selection of lighting classes using this system are given in Annex E. 6.2.2 Adaptive Lighting As indicated in 6.2.1, the normal lighting class is selected using the most onerous parameter values, and the application of this class may not be justified throughout the hours of darkness (This might be under changing conditions e.g. weekends, different weather conditions). Temporal changes in the parameters under consideration when selecting the normal lighting class could allow, or may require, an adaptation of the normal level of average luminance or illuminance, usually by reducing the level. The most important parameters in this respect are likely to be traffic volume and composition and weather conditions, but ambient luminance can also have an influence. The adapted lighting level or levels should be the average luminance or illuminance from a class or classes in the same table from which the normal lighting class has been selected. Tables 1, 3 and 6 can be used to select the appropriate adapted lighting class or classes for different periods of the hours of darkness when the value of the selection parameters is significantly different. The examples of the use of the tables in Annex E include the selection of the adapted lighting classes, and it can be seen that only the average level of luminance or illuminance is varied. It is important that the changes in the average lighting level do not affect the other quality criteria outside the limits given in the system of M, C or P lighting classes. Reducing the light output from every lamp by the same amount using dimming techniques will not affect luminance or illuminance uniformity, or the object contrast, but the threshold contrast increases. Reducing the average level by switching off some luminaires will not fulfil the quality requirements and is not recommended. The use of adaptive lighting can provide significant reduction in energy consumption, compared with operating the normal lighting class throughout the night. It can also be used to reduce energy consumption by reducing the lamp light output to the maintained value when the installation is clean and the lamps are new. Where the pattern of variation in parameter values is well known, such as from a record of traffic counts on traffic routes, or can be reasonably assumed, as in many residential areas, a simple time based control system may be appropriate. In other situations an interactive control system linked to real-time data may be preferred. This approach will permit the normal lighting class to be activated in the case of road works, serious accidents, bad weather or poor visibility. NOTE An exceptional situation occurs when traffic volume has been a criterion to provide a lighting system. In those situations, and if no other criterion prevents it, reduction to a lighting level lower than M6 after rush hours may be considered. This is mainly applicable for motorways, which are in general highly predictable and without oncoming traffic, sharp bends and intersections (Dutch Ministry of Transport, Public Works and Water Management, 2006). If, for instance, the only criterion to provide a lighting system is that the average peak hour traffic intensity exceeds a predefined level n vehicles per hour, a reduction to a level lower than M6 might be considered when the actual traffic intensity is lower than n. A system operating at such a low level cannot be classified as road lighting; it is a system of visual guidance.

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This, together with environmental arguments, leads to the decision to reduce the lighting level on motorways to a level lower than M6 when traffic volume in vehicles/hour/lane is less than a certain number n. This level serves no other purpose than to offer guidance to road users (see 5.6 "positional level"). In nature areas, environmental arguments are regarded as even more important than guidance for road users. Thus, in nature areas lighting is switched off if traffic intensity is lower than n motor vehicles/lane/hour. When traffic intensity exceeds x motor vehicles/hour/ lane, lighting will be switched to the normal level (e.g. n = 800 and x = 1 100, Dutch Ministry of Transport, Public Works and Water Management, 2004 and 1999). 7 REQUIREMENTS FOR MOTORIZED TRAFFIC 7.1 The Luminance Concept The M lighting classes are intended for drivers of motorized vehicles on traffic routes, and in some countries also on residential roads, allowing medium to high driving speeds. The lighting classes M1 to M6 are defined by the lighting criteria given for each class in Table 2. The application of these classes depends on the geometry of the relevant area and on the traffic and time dependant circumstances. The appropriate lighting class has to be selected according to the function of the road, the design speed, the overall layout, the traffic volume and composition, and the environmental conditions. For the determination of the M lighting class to be applied the appropriate weighting values for the different parameters have to be selected and added to find the sum of the weighting values (VWS). The number of the lighting class M is then calculated as: Number of lighting class M = 6 - VWS Careful selection of appropriate weighting values in Table 1 will yield class numbers between 1 and 6. If the result is not a whole number, use the next lower whole number.

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Table 1. Parameters for the selection of M lighting class. Parameter Speed

Traffic volume

Traffic composition Separation of carriageways Intersection density Parked vehicles Ambient luminance Visual guidance / traffic control

10

Options Very high High Moderate Very high High Moderate Low Very low Mixed with high percentage of non-motorized Mixed Motorized only No Yes High Moderate Present Not present High Moderate Low Poor Moderate or Good

Weighting Value Vw 1 0,5 0 1 0,5 0 -0,5 -1 2 1 0 1 0 1 0 0,5 0 1 0 -1 0,5 0 Sum of Weighting Values

Vw Selected

VWS

CIE 115:2010

The controlling criteria for the lighting of roads for motorized traffic are the luminance level and uniformity of the carriageway, the illuminance level of the surrounds of the road, the limitation of disability and discomfort glare, and the requirements for direct visual guidance. Direct visual guidance is considered in 7.2. For the other criteria recommended values are given in Table 2 for the lighting classes M1 to M6, reflecting various traffic situations. For advice on appearance and environmental aspects see clause 10. The lighting criteria used are the maintained average road surface luminance (Lav), the overall (Uo) and longitudinal (Ul) uniformity of the luminance, the surround ratio (Rs), and the threshold increment (fTI). These values apply to roads, which are sufficiently long so that the luminance concept can be used, outside conflict areas and/or outside areas with measures of traffic calming. The surround ratio is considered for roads with adjacent footpath/cycle path only when no specific requirements are given (see P lighting classes. Table 2. Lighting classes for motorized traffic, based on road surface luminance. Road surface Lighting class

Dry

Lav in cd·m-2

Threshold increment

Surround ratio

Wet *

Uo

Ul

Uo

fTI in %

Rs

M1

2,0

0,40

0,70

0,15

10

0,5

M2

1,5

0,40

0,70

0,15

10

0,5

M3

1,0

0,40

0,60

0,15

15

0,5

M4

0,75

0,40

0,60

0,15

15

0,5

M5

0,50

0,35

0,40

0,15

15

0,5

M6

0,30

0,35

0,40

0,15

20

0,5

*Applicable in addition to dry condition, where road surfaces are wet for a substantial part of the hours of darkness and appropriate road surface reflectance data are available. NOTE The use of luminance concept requires the knowledge of the reflection properties of the road surface. They are taken into account either through the real properties (measurements) or through a reference r-table such as the C and R standards defined by the CIE (CIE 132-1999 and CIE 144:2001). However, recent measurements have shown that the current pavements used on roads vary largely with time and are very different from the CIE standards (which were defined decades ago), frequently leading to errors between 30 % and 100 % in terms of average luminance (CHAIN et al., 2007). When designing a lighting installation using the luminance concept it is thus important to have an accurate representation of the photometric characteristics of the road surface at its stabilized situation. If the measurement of the r-table in laboratory is not possible, real road reflectance properties may be measured on site with portable devices. If not possible, the current CIE standards remain the latest recommended rtables to use for the calculation. In all cases, it is necessary to systematically evaluate a representative value of the average luminance coefficient q0.

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7.2 Practical Considerations for Direct Visual Guidance No method of quantifying direct visual guidance (see 5.7) has been devised, but certain practical considerations are helpful. Sometimes, the pattern of direct light from the road lighting luminaires can be misleading. This can be avoided at the design stage by considering the pattern in perspective, that is, how the alignment and arrangement of the luminaires appears to the road user. Direct visual guidance can be enhanced by a change to a light source of a different colour at junctions, roundabouts, etc. The change should be consistent in an area and intentional. 8 THE LIGHTING OF CONFLICT AREAS Conflict areas occur whenever vehicle streams intersect each other or run into areas frequented by pedestrians, cyclists, or other road users, or when there is a change in road geometry, such as a reduced number of lanes or a reduced lane or carriageway width. Their existence results in an increased potential for collisions between vehicles, between vehicles and pedestrians, cyclists, or other road users, or between vehicles and fixed objects. Parking areas and toll-stations are also regarded as conflict areas. General circulation areas at outdoor working places are covered by CIE S 015/E:2005. NOTE 1 Pedestrian crossings may require special consideration; they are not subject of this report. In some countries, national standards exist which give further guidance relative to national practices. Pedestrian crossings minimum requirements should be in accordance with CIE 136-2000, clause 2.4.2. The lighting should reveal the existence of the conflict area, the position of the kerbs and road markings, the directions of the roads, the presence of pedestrians, other road users, and obstructions, and the movement of vehicles in the vicinity of the conflict area. Where no lighting is otherwise provided on a road leading to or leaving the conflict area, the selected lighting class should be installed for a stretch long enough to provide about 5 seconds of driving distance at the expected traffic speed. The lighting classes C0 to C5 are defined by the lighting criteria given for each class in Table 5.

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Table 3. Parameters for the selection of C lighting class. Parameter

Options

Very High High Speed Moderate Low Very high High Traffic volume Moderate Low Very low Mixed with high percentage of nonmotorized Traffic composition Mixed Motorized only No Separation of carriageways Yes High Ambient luminance Moderate Low Poor Visual guidance / traffic control Moderate or good

Weighting Value Vw

Vw Selected

3 2 1 0 1 0,5 0 -0,5 -1 2 1 0 1 0 1 0 -1 0,5 0 Sum of Weighting Values

VWS

For the determination of the C lighting class to be applied the appropriate weighting values in Table 3 for the different parameters have to be selected and added to find the sum of the weighting values (VWS). The number of the lighting class C is then calculated as: Number of lighting class C = 6 - VWS Careful selection of appropriate weighting values will yield class numbers between 0 and 5. If the result is not a whole number, use the next lower whole number. For conflict areas, luminance is the recommended design criterion. However, where viewing distances are short and other factors prevent the use of luminance criteria, illuminance may be used on a part of the conflict area, or the entire area if the luminance criteria cannot be applied to the whole area. The correspondence between luminance and average horizontal illuminance depends on the lightness of the road surface, as represented by the q0 value of that surface. Table 4 gives the relationship between the M and C classes for three examples of q0 values.

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Table 4. M and C lighting classes of comparable lighting level for different values of q0 for the road surface. Lighting class M

M1

Average luminance L in cd·m-2

2,0

M2 1,5

M3 1,0

M4

M5

M6

0,75

0,50

0,30

Lighting class C if q0 = 0,05 cd·m-2·lx-1

C0

C1

C2

C3

C4

C5

Average illuminance E in lx

50

30

20

15

10

7,5

Lighting class C if q0 = 0,07 cd·m-2·lx-1

C0

C1

C2

C3

C4

C5

Average illuminance E in lx

50

30

20

15

10

7,5

C5

Lighting class C if q0 = 0,09 cd·m-2·lx-1

C0

C1

C2

C3

C4

Average illuminance E in lx

50

30

20

15

10

7,5

The conflict area should as a minimum have a lighting level no lower than that of the connecting roads. However, it is recommended that the lighting class used for the conflict area should normally be one step higher than the highest lighting class used for the road or roads leading to the conflict area (e.g. M2 instead of M3). This will not be possible where the entrance roads are lit to Class M1. In this case, the conflict area should also be lit to class M1. Where illuminance is used as a criterion for the conflict area lighting, it is necessary to consider comparable luminance and illuminance classes (M and C classes respectively from Tables 2 and 5.) Table 4 gives comparable M and C classes for various values of q0 for the road surface. Row 1 gives the M classes from which the luminance class used for the most important road leading to the conflict area is selected. The equivalent illuminance C class is then taken from column 1, depending on the q0 value. The actual C class to be used in the conflict area is recommended to be one step higher than the equivalent class so determined. (e.g. if the most important road leading to the conflict area is M4 and q0 = 0,07 cd·m-2·lx-1, the equivalent class is C4 and the conflict area is recommended to be lit to class C3.) Where luminance is used as a criterion for the conflict area lighting, it is necessary to calculate threshold increment TI (symbol fTI), for relevant observer positions and viewing directions in the conflict area, which requires knowledge of veiling luminances and adaptation luminances for the particular observer positions and viewing directions (ANSI, 2005). NOTE 2 The calculation method is described in CIE 140-2000 together with the limits of application to be observed. Following the procedure for the moving observer as given in CIE 140-2000 there are no restrictions in terms of observer positions and viewing directions in conflict areas. The formula for the calculation of veiling luminances is valid for any one observer position and particular viewing direction - provided the limits are observed (see also CIE 31-1976). The increments in which the observer is moved forwards along the straight section of the road with a regular luminaire arrangement could also be used in the conflict area. The number of luminaires to be taken into account is not very critical as long as all luminaires in the conflict area are considered, and the observer

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is moved in increments of not more than 3,0 m. The nearest luminaire to the observer at an angle of 20° or less above the horizontal will usually contribute most. The actual average luminance is calculated from the average illuminance of the conflict area. If the reflection properties are known in terms of r-tables and average luminance coefficient q0, the average luminance L can be calculated from the knowledge of the average illuminance E using the formula L = q0 E . If only the diffuse reflectance formula L =

ρ

π

ρ

is known the average luminance can be calculated using the

E . If nothing is known regarding the reflection properties an

average luminance coefficient q0 of 0,07 cd·m-2·lx-1 could be applied as shown in Table 4, or an average reflectance ρ of 0,20 could be applied. An indication of road reflection properties could be obtained by direct measurements. If appropriate reflectance tables are available, the accuracy of the luminance design can be significantly improved. This can lead to considerable savings in investments and energy usage. NOTE 3 In some conflict areas where viewing distances are short and there are multiple observer positions and luminaire orientations, the use of TI may be impractical. An alternative solution in such situations is the use of luminaire intensity limitation as discussed in Annex D. Table 5. Lighting classes for conflict areas.

Lighting Class

Average Illuminance over whole of used surface E in lx

C0

Uniformity of Illuminance

Threshold increment fTI in % 1)

Uo(E)

High and moderate speed

Low and very low speed

50

0,40

10

15

C1

30

0,40

10

15

C2

20

0,40

10

15

C3

15

0,40

15

20

C4

10

0,40

15

20

C5

7,5

0,40

15

25

1)

Applicable where visual tasks usually considered for the lighting of roads for motorized traffic (M classes) are of importance. 9 ROAD LIGHTING FOR PEDESTRIANS 9.1 General The visual task and needs of the pedestrian differ from those of the driver in many respects. Speed of movement is less and objects that are close to the pedestrian are more important than those in the distance. The surface pattern and texture of objects on the road and footway are important to the pedestrian, but less so to the motorist, for whom silhouette vision predominates. These differences indicate that the lighting criteria which meet the needs of the motorist may not meet the needs of the pedestrian, and vice versa. The benefits of good quality lighting in residential streets are summarized in CIE 136-2000. Besides improving the general amenity level, good lighting discourages crime

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against the person and property, makes the detection of crime easier, and imparts a greater sense of security in a neighbourhood. Residential lighting is, therefore, often installed or upgraded as a measure against crime and is assuming an increasing importance in this role, particularly in urban areas. 9.2 Crime and Lighting Studies Most of the studies of crime and lighting have been conducted by measuring the crime rates before and after upgrading the lighting, or by interviewing local residents to record their opinion about the effectiveness of the upgrading. These studies have been recorded in the USA (Tien, 1979), UK (Painter, 1988, 1989), Japan (Kansai, Report No 4, 1989), and France (Marinier, 1983). Not all of them provide data that are soundly based but taken as a whole; they suggest the improvement of the lighting performance can directly reduce the number of acts of crime and harassment. Newly installed or upgraded lighting can displace crime to an adjoining area. A UK study (Lloyd and Wilson, 1989) found such displacement, but a study by Schreuder (Lux Europa, 1993) showed an overall reduction without displacement.. These studies also indicate that fear of crime, which can be as harmful as crime itself, is reduced by good lighting. This fear has an adverse affect on morale in a neighbourhood and deters residents from coming out of their houses at night. Not only does this increase the sense of isolation of the residents but it provides greater opportunities for criminals, because there are fewer people to observe or restrain them. Thus, the lighting contributes also to indirect effects through the self-confidence and the pride it generates. It creates also a social control that can be either formal (real supervision) or informal (climate of supervision). It is not known precisely which luminous characteristics, for which cultural and social context, with which mechanism, the lighting (or its improvement) can have an impact on urban security. The debate, on methodological, theoretical and prescriptive aspects continues (CERTU, 2006). Where the fear of crime is an aspect to be considered, facial recognition should be taken into account. Additional requirements in this case are given in Tables 6 and 7. 9.3 Road Accidents in Residential Areas CIE 93-1992 indicates that the provision of lighting on motorways and arterial routes to recognized standards will reduce the number and severity of accidents at night. In residential areas, however, there are generally few road accidents, and lighting on residential roads is therefore not provided mainly to avoid accidents involving vehicles, although it can provide guidance for drivers. It is mainly provided to give safe passage for pedestrians so that they can see obstacles and other people, can find their way on foot, and have a feeling of safety and security. 9.4 Quality Criteria The road lighting should enable pedestrians to discern obstacles or other hazards in their path and be aware of the movements of other pedestrians, friendly or otherwise, who may be in close proximity. For this, the lighting on both horizontal and vertical surfaces, as well as the control of glare and the colour rendering, is important. Environmental issues should be taken into account. 9.4.1 Lighting of Horizontal Surfaces To ensure that the pedestrian can move over the road and footpath surfaces in safety, the horizontal illuminance, Eh, must be adequate. Horizontal illuminance is measured at ground level in terms of average and minimum values, and applies to the whole of the used surface, which usually comprises the footways and the carriageway surface, unless the carriageway is treated separately under the provisions for motorized traffic in clause 7. 9.4.2 Lighting of Vertical Surfaces Adequate lighting of vertical surfaces is necessary for facial recognition, which may also enable an act of aggression to be anticipated. The quantification of this presents a difficulty

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because of the multiplicity of planes at each measurement point which have to be taken into account. An attempt to overcome this has been made by considering the illuminance on an infinitesimal vertical half cylinder situated at head height (1,5 m). This measure, the semicylindrical illuminance, Esc, has been introduced in CIE136-2000, as an adjunct to horizontal illuminance. For its measurement a special adaptation is required to the mounting of the photoelectric detector which is used to measure planar illuminance. 9.4.3 Control of Glare The control of discomfort and disability glare is not as critical as for the motorist, because speed of movement is much lower, giving a greater reaction time. No method of quantifying glare has been agreed to internationally, but a number of methods are in current use on a national basis. Methods for quantifying and controlling glare in pedestrian and low speed traffic areas are given in Annex D. 9.4.4 Choice of Light Source Monochromatic light sources should be avoided for areas where the crime risk is high, that are environmentally sensitive, or where pedestrian activities predominate. Using light sources with better colour rendering properties will improve the possibility to see colour contrasts and contributes to a better facial recognition. This could be of particular importance for elderly or visually impaired users of pedestrian and low speed traffic areas. NOTE The use of low-pressure sodium lighting is considered a positive environmental step in areas with sensitive optical astronomical facilities and near sea turtle nesting areas. 9.5 Lighting Levels for Pedestrian and Low Speed Traffic Areas The parameters relevant for the selection of an appropriate P lighting class for a given pedestrian or low speed traffic area are summarized in Table 6. The lighting classes P1 to P6 are defined by the lighting criteria given for each class in Table 7. They are intended for pedestrians and pedal cyclists on footways, cycleways, and other road areas lying separately or along the carriageway of a traffic route, and for residential roads, pedestrian streets, parking places, etc.

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Table 6. Parameters for the selection of P lighting class. Parameter Speed

Traffic volume

Traffic composition

Parked vehicles

Options Low

1

Very low (walking speed)

0

Very high

1

High

0,5

Moderate

0

Low

-0,5

Very low

-1

Pedestrians, cyclists and motorized traffic

2

Pedestrians and motorized traffic

1

Pedestrians and cyclists only

1

Pedestrians only

0

Cyclists only

0

Present

0,5

Not present

0

High

1

Ambient luminance Moderate Low Facial recognition

Weighting Value Vw

Vw Selected

0 -1

Necessary

Additional requirements

Not necessary

No additional requirements Sum of Weighting Values

VWS

The application of these classes depends on the geometry of the relevant area and the traffic and time dependant circumstances. For the determination of the P lighting class to be applied, the appropriate weighting values in Table 6 for the different parameters have to be selected and added to find the sum of the weighting values (VWS). The number of the lighting class P is then calculated as: Number of lighting class P = 6 – VWS Careful selection of appropriate weighting values will yield class numbers between 1 and 6. If the result is not a whole number, use the next lower whole number.

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Table 7. Lighting classes for pedestrian and low speed traffic areas.

Lighting Class

Average Minimum horizontal horizontal illuminance illuminance

Additional requirement if facial recognition is necessary Minimum vertical Illuminance Ev,min in lx

Minimum semicylindrical illuminance Esc,min in lx

3,0

5,0

3,0

10

2,0

3,0

2,0

P3

7,5

1,5

2,5

1,5

P4

5,0

1,0

1,5

1,0

P5

3,0

0,6

1,0

0,6

P6

2,0

0,4

0,6

0,4

Eh,av

Eh,min

in lx

in lx

P1

15

P2

NOTE 1. To provide for uniformity the actual value of the maintained average illuminance may not exceed 1,5 times the value indicated for the class. 2. A high colour rendering contributes to a better facial recognition.

10 APPEARANCE AND ENVIRONMENTAL ASPECTS 10.1 Energy Conservation A worldwide consensus is evolving on the need to reduce electrical energy consumption because of global climate change. This report takes account of this need in a number of ways to ensure that only the appropriate and necessary level of lighting is provided for any situation at any point in time: -

-

NOTE

The recommendations given in this Technical Report relate to the minimum maintained photometric values, so that the lighting design can limit the energy consumption taking account of the maintenance plan defined for the project. Guidance is given on the adaptation of lighting level over time taking account of the variations in traffic volume and composition and other relevant parameters, whilst respecting traffic safety and personal security, so that energy consumption can be reduced compared with non-adaptive designs. The CIE will continue to prepare some lighting documents for the intelligent use of lighting according to the statement on energy conservation.

10.2 Appearance The design and position of street furniture can make a great difference to the street scene, both by day and by night. Consideration should be given to the appearance of the lighting installation by day as affected by the: -

height of the lighting columns in relation to the surrounding buildings and trees; location of the lighting columns with respect to views of scenic value; obstruction should be as little as possible; design of supporting elements; complexity of the lighting arrangement; design of luminaires.

In environmentally sensitive areas, the use of a light source which allows colour discrimination should be considered. 19

CIE 115:2010

10.3 Obtrusive Light Public lighting provided for the purpose of all-night safety and security on public roads, cycle paths, footpaths and pedestrian areas is in some cases regarded as obtrusive. Obtrusive light is defined as light, outside the area to be lit, which, because of quantitative, directional or spectral attributes in a given context, gives rise to annoyance, discomfort, distraction or a reduction in the ability to see essential information. Details on effects and relevant technical parameters are provided e.g. in the CIE Technical Report Guide on the Limitation of the Effects of Obtrusive Light from Outdoor Lighting Installations (CIE 150:2003). Regarding the lighting of roads only two effects are discussed here, the effects on residents and on astronomical observations. The light from road lighting installations could be annoying where it enters rooms of a dwelling which are normally dark, e.g. bedrooms. The illuminance of vertical surfaces (windows) is an indicator of this effect. The direct view of bright luminaires from normal viewing positions could cause annoyance, distraction or even discomfort. The luminance level of the lighting emitting parts of a luminaire in a specific direction would be an indicator of this effect. The curfew concept, taking into account the time after which more stringent lighting control should be applied (as defined in CIE 126-1997), should be considered during the design phase to reduce the effects of the obtrusive lighting produced by road lighting to within tolerable limits for residents at any period of the night. Astronomical observations are affected by artificial sky glow, i.e. the brightening of the night sky that results from the reflection of radiation (visible and non-visible), scattered from the constituents of the atmosphere in the direction of observation (CIE 126-1997). It includes radiation that is emitted directly upwards from the luminaires and radiation that is reflected from the surfaces of the earth. The use of adaptive lighting can significantly reduce obtrusive light during the periods when adapted lighting classes with dimmed light output are in use. Light above the horizontal should be minimized (see CIE 126-1997). 11 VISIBILITY CONCEPT AND MESOPIC VISION This report is based on the luminance concept and photopic vision. Considering visibility, the TC 4-36 document Visibility Design for Roadway Lighting gives the current state of knowledge on how to predict visibility. Three methods are described: -

Visibility Level (VL) on plane and spherical targets, Small Target Visibility (STV) on plane targets, Revealing Power (RP) concept as a percentage of the road surface area where visibility can occur for plane targets.

Visibility of objects in the eye’s peripheral field of view is enhanced when white light sources are used at typical road lighting levels (He et al., 1997). This may be of considerable importance, as peripheral vision is believed to be significant in relation to night time road safety (CIE x028:2005). The amount of benefit of improved peripheral vision has not yet been determined (TAC, 2006). The Mesopic Optimization of Visual Efficiency (MOVE) consortium has published a practical system for mesopic photometry in road lighting dimensioning (Eloholma and Halonen, 2006). There may be substantial differences in dimensioning low luminance levels of road lighting depending on whether photopic or mesopic photometry is used. (This subject is being dealt with in CIE TC 1-58 Visual Performance in the Mesopic Region.)

20

CIE 115:2010

12 REFERENCES 1.

ADRIAN, W. Visibility of targets: model for calculation. Lighting Research and Technology 21/4, 181-188, 1989.

2.

ANSI (American National Standard Institute). Recommended Practice for Roadway Lighting. ANSI/IES RP-8-05, 2005.

3.

BS 5489-1:2003. Code of practice for the design of road lighting - Part 1: Lighting of roads and public amenity areas, 2003.

4.

CEN TR 13201-1:2003. Selection of Lighting Classes, 2003.

5.

CERTU 2006. Lighting, a Dynamic Weight in Urban Policies. C. Chain, Certu - Centre d’Études sur les Réseaux, les Transports, l’Urbanisme et les Constructions Publiques, 2006.

6.

CERTU 2008. National Road Lighting: Use of the European Norm EN 13201. C. Chain, Certu - Centre d’Études sur les Réseaux, les Transports, l’Urbanisme et les Constructions Publiques, 2008.

7.

CHAIN, C., LOPEZ, F., VERNY, P. Impact of Real Road Photometry on Public Lighting Design. Proceedings of the 26th Session of the CIE, Beijing. D4.26-29, 2007.

8.

CIE 31-1976. Glare and Uniformity in Road Lighting Installations, 1976.

9.

CIE 47-1979. Road Lighting for Wet Conditions, 1979.

10. CIE 93-1992. Road Lighting as an Accident Countermeasure, 1992. 11. CIE 100-1992. Fundamentals of the Visual Task of Night Driving, 1992. 12. CIE 115-1995. Recommendations for the Lighting of Roads for Motor and Pedestrian Traffic, 1995. 13. CIE 126-1997. Guidelines for Minimizing Sky Glow, 1997. 14. CIE 132-1999. Design Methods for Lighting of Roads, 1999. 15. CIE 136-2000. Guide to the Lighting of Urban Areas, 2000. 16. CIE 140-2000. Road Lighting Calculations, 2000. 17. CIE 144: 2001. Road Surface and Road Marking Reflection Characteristics, 2001. 18. CIE 150:2003. Guide on the Limitation of the Effects of Obtrusive Light from Outdoor Lighting Installations, 2003. 19. CIE 154:2003. The Maintenance of Outdoor Lighting Systems, 2003. 20. CIE 180:2007. Road Transport Lighting for Developing Countries, 2007. 21. CIE DS 017.2/E:2009. International Lighting Vocabulary, 2009. 22. CIE S 015/E:2005. Lighting of Outdoor Work Places, 2005. 23. CIE x028:2005. Proceedings of the CIE Symposium ’05: Vision and Lighting in Mesopic Conditions, 2005. 24. Dutch Ministry of Transport, Public Works and Water Management (Ministerie van Verkeer en Waterstaat, the Netherlands). Dynamic public lighting, Rotterdam, 1999. 25. Dutch Ministry of Transport, Public Works and Water Management (Ministerie van Verkeer en Waterstaat, the Netherlands). Lighting implementation framework, Rotterdam, 2004. 26. Dutch Ministry of Transport, Public Works and Water Management (Ministerie van Verkeer en Waterstaat, the Netherlands). Manual of dynamic motorway lighting, Rotterdam, 2006. 27. ELOHOLMA, M., HALONEN, L. New Model for Mesopic Photometry and its Application to Road Lighting. Leukos 2(4), 263-293, 2006.

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CIE 115:2010

28. HE, Y., REA, M., BIERMAN, A., BULLOUGH, J. Evaluating Light Source Efficacy Under Mesopic Conditions Using Reaction Times. J. Illuminating Eng. Soc., 26, 125-138, 1997. 29. Kansai Regional Branch of the Illuminating Engineering Institute of Japan. Report No.4 of the Committee on the Improvement of Street Lighting, 1989. 30. LE GRAND, Y. Light, Colour and Vision, 2nd edition. Chapman and Hall, London, 1957. 31. LLOYD, R., WILSON D. Inner City Street Lighting and its Effect upon Crime. ILE Conference, Bournemouth, 1989. 32. MARINIER, J.-C. Public Lighting Reduces Mugging, Lux, 123, 38-40, 1983. 33. PAINTER, K. Lighting and Crime Prevention. The Edmonton Project, Middlesex Polytechnic, Centre for Criminology, 1988. 34. PAINTER, K. Lighting and Crime Prevention for Community Safety. The Tower Hamlets Study, First Report, London, Middlesex Polytechnic, Centre for Criminology, 1989. 35. SCHREUDER, D.A. The Relation between Lighting Accidents and Crime in Urban Streets. Lux Europa, Vol. 1, 117-123, 1993. 36. Transportation Association of Canada (TAC). Guide for the Design of Roadway Lighting, 2006. 37. TIEN, J., O'DONNEL, V.F., BARNETT, A., MIRCHANDANI, P.B. Street lighting Projects. National evaluation program, Phase 1 Report, Washington DC: National Institute of Law Enforcement and Criminal Justice, 1979. 38. UNI 11248:2007. Road lighting – selection of lighting classes, 2007.

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CIE 115:2010

ANNEX A: EXAMPLE OF ECONOMIC CALCULATIONS It is necessary to know the capital and operating costs of a lighting system at the following stages in a project: -

when the need for lighting is evaluated when the priority of projects is determined when the implementation program is planned when different lighting designs and arrangements are compared in cost estimates in budgets

The following clauses describe an example of an algorithm to evaluate cost and profitability. A.1 Costs Evaluation of many large road construction projects is based on the life cycle costs method (LCC). This method is also useful for road lighting installations. Life cycle consists of consecutive and interlinked stages of a product system, from raw material acquisition or generation of natural resources to the final disposal. Life cycle costs include installation, maintenance, energy, demolition, recycling and final disposal costs. It is important to include the whole life cycle costs in the calculation. Considerable costs during operation result from energy consumption and maintenance. Greater initial investment may result in lower energy and maintenance costs and lead to lower life cycle costs. For example long lasting good quality lighting equipment is usually more expensive but the maintenance costs are smaller. Thus life cycle costs will decrease compared to the poor quality lighting equipment. All necessary costs can be calculated from the following formulae: 1) Installation costs (per road metre):

C in =

m C co + n C lu + S C ps S

(A.1)

where

Cin

is installation costs (per road metre) (€);

m

number of columns on the cross-section (e.g. 2 for opposite array, 1 for centre median array);

Cco

cost of the column and the foundation per unit (€);

n

number of luminaires on the cross-section;

Clu

cost of the luminaire and the first lamp(s) per unit (€);

S

spacing of the columns (m);

Cps

cost of the power supply mains per road metre (€).

2) Operating costs (per road metre):

t 1 n Plu C en + C op =

n C gr t2 S

+ q n C ir + m C fi (A.2)

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CIE 115:2010

where

Cop

is operating costs of the first year per road metre (€);

t1

annual burning time (h);

t2

life time of the lamp (a);

n

number of luminaires on the cross-section;

Plu

power of the luminaire (kW);

Cen

cost of the energy (€/kWh);

Cgr

cost of the group replacement of the lamps per unit (€);

Cir

cost of the individual replacement of the lamp per unit (€);

q

relative number of individual replacement of lamps per year;

m

number of columns on the cross-section;

Cfi

fixed costs per column (€);

S

spacing of the columns (m).

3) Life cycle costs (per road metre): a) Present value method:

C lc = C in +

1 − (1 + p ) − t

p

C op +

1

(1 + p ) t

Vr

(A.3)

where

Clc

is present value of life cycle costs per road metre (€);

Cin

installation costs per road metre (€);

p

interest rate;

t

length of the examination period (years);

Cop

operating costs of the first year per road metre (€);

Vr

residual value (€).

b) Average annual costs method (calculated at the mid-point of the service life t):

C aa = α t C in + β t C op where

24

Caa

is average annual costs per road metre and year (€);

αt

capital recovery factor;

βt

growth factor of operating costs;

Cin

installation costs per road metre (€);

Cop

operating costs of the first year per road metre (€).

(A.4)

CIE 115:2010

A.2 Profitability of Road Lighting The profitability of road lighting in terms of traffic economy is analysed by comparing the average annual savings in total costs of road traffic with the combined influence of lighting costs and the costs of column collisions. The traffic volume required to make road lighting profitable is obtained by performing the analysis after half of the service life (t) of the road lighting system has passed (t is usually 20 years), cf. formula (A.5). All factors, coefficients, unit prices etc. must be in accordance with the national statistics.

V ADT =

t /2 10 8 ⎡C aa + b N c C cc (1 + r1 / 100 ) ⎤ Rbc ⎣⎢

⎦⎥

365 b ⎡1,1 p d g C pa (1 + r2 / 100 )

⎢⎣

t /2

+ S tc ⎤ ⎥⎦

(A.5)

where

VADT Caa b Nc Ccc r1 Rbc

is the average daily traffic volume (vehicles/d); average annual costs of road lighting per km (€), according to formula (A.4); traffic growth factor; number of columns per km; costs of a column collision 1) (€); annual growth in costs of column collisions (%); benefit-cost ratio;

Coefficient 1,1 includes material damages;

t p d g Cpa r2 Stc

service life of lighting system (a); proportion of night-time traffic; reduction in night-time accidents due to road lighting; personal injuries and fatality accident rate on the road section (accidents/(108 vehicle km)); costs of personal injuries and fatality accident (€); annual growth in costs of personal injuries and fatality accidents (%); savings in time costs per vehicle km (€/km), according to formula (A.6).

1)

This cost is the total cost to the community, including injury or fatality costs. If passively safe columns are used the injury cost element can usually be taken as zero.

t ⎛ 1 1 ⎞⎛ r ⎞2 S tc = p V t t ⎜ − ⎟ ⎜ 1 + 3 ⎟ ⎝ v1 v 2 ⎠ ⎝ 100 ⎠

(A.6)

where

p Vtt r3 v1 v2

is the proportion of night-time traffic; the value of traffic time (€/h); annual growth in value of time in traffic (%); night-time speed before road lighting (km/h); night-time speed after installation of road lighting (km/h);

1 1 savings in time per vehicle km (h/km). − v1 v2

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A.3 Examples Calculations are based on the Finnish unit prices and coefficients from the year 2006. 1) Installation costs (per road metre):

C in =

m C co + n C lu + S C ps

(A.7)

S Example 1

Example 2

Motorway, lighting class M2, lamps ST-250, twin-central arrangement, mounting height 12 m and rigid columns between guard rails.

Sub-urban two-lane main street, lighting class M4, lamps ST-250, single-sided arrangement, mounting height 10 m, earth cables and energy absorbing columns.

1

0001

960 €

1 056 €

2

0001

Clu

220 €

220 €

S

53 m

056 m

Cps

24 €

022 €

Cin

50,42 €

44,79 €

m Cco n

2) Operating costs of the first year (per road metre):

t 1 n Plu C en +

n C gr

C op =

t2

+ q n C ir + m C fi

(A.8)

S Example 3

Motorway, no against columns

impact

Example 4 collisions

Sub-urban two-lane main street, energy absorbing columns

t1

4 000 h

4 000 h

t2

4

4

n

2

1

Plu

0,284 kW

0,284 kW

Cen

0,06 €/kWh

0,06 €/kWh

Cgr

22 €

22 €

Cir

37 €

37 €

q

0,15

0,15

m

1

1

Cfi

34 €

34 €

S

53 m

56 m

Cop

3,63 €

2,02 €

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3) Life cycle costs (per road metre): Average annual costs method (average annual costs per road metre and year, calculated at the mid-point of the service life t):

C aa = α t C in + β t C op .

(A.9)

Considering installations with •

service life of lighting: 20 years,

•

interest rate: 6 %,

•

annual growth of operating costs: 2 %,

the capital recovery factor αt = 0,087 and the growth factor of operating cost βt = 1,49. Example 5: Motorway

Caa = 0,087 × 50,42 € + 1,49 × 3,63 € = 9,80 € Example 6 : Two-lane main street

Caa = 0,087 × 44,79 € + 1,49 × 2,02 € = 6,90 € Profitability of road lighting:

V ADT =

t /2 10 8 ⎡C aa + b N c C cc (1 + r1 / 100 ) ⎤ Rbc ⎢⎣

365 b ⎡1,1 p d g C pa (1 + r2 / 100 ) ⎢⎣

⎥⎦

t /2

(A.10)

+ S tc ⎤ ⎥⎦

Example 7

Example 8

Motorway

Two-lane main street

9 800 €

6 900 €

b

1,4

1,4

Nc

1 000:53

1 000:56

Ccc

0 (columns between guard rails)

170 €

r1

0%

2%

Rbc

2

2

t

20 years

20 years

p

0,3

0,3

d

0,2

0,3

g

7

20

386 800 €

386 800 €

r2

2%

2%

Stc

0€

0€

17 608 veh/d

5 065 veh/d

Caa

Cpa

VADT

Savings in the time costs (Stc) are not taken into account. Speed limits restrict to use higher driving speed due to road lighting. 27

CIE 115:2010

ANNEX B: ROAD LIGHTING UNDER SNOW CONDITIONS In countries where the road and its surroundings are snow-covered during their winter season, the snow will change the visual conditions in several ways. Recently fallen snow covering the road surface will (for night time conditions) provide excellent visual conditions. Unless the lighting level is reduced, the luminance of the road will be very high and glare from the road lighting may be excessive. Even with reduced lighting, the reflectance of the snow will be high enough to show most obstacles with a high level of negative contrast. On the other hand, the driving task may become more demanding if the road becomes slippery with ice, the snow will cover road markings, and in some cases the traffic signs may be covered by snow as well. The visually favourable situation will become less favourable situation when the snow is melted away by salt or milder weather. This will leave the surface moist and soiled for some time. The road markings will in some cases still be invisible until the road is cleaned. The snowy conditions will under some conditions offer possibilities for reducing the lumen output of the lamps. But rather complicated driving situations and intermittent poor visual conditions may also appear and will necessitate careful operation of the lighting system if the levels are adapted during the winter season.

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ANNEX C: THRESHOLD INCREMENT TI [fTI] In road lighting, it is common to describe the effects of light scattered in the eye by threshold increment TI (CIE 31-1976). The calculation of TI is described in CIE 140-2000 and CIE 150:2003. The threshold increment TI (fTI) is calculated from the formula (C.1):

fTI =

65 Lv (%) L0,8 av

for 0,05 cd·m-2 < Lav < 5 cd·m-2

(C.1a)

fTI =

95 Lv (%) L1,05 av

for Lav ≥ 5 cd·m-2

(C.1b)

with n

Eeye,i

i =1

Θi2

Lv = k ∑

(C.2)

where

Lv

is the veiling luminance in cd·m-2 for n luminaires in the field of view;

Lav

is the relevant value of the observer’s adaptation luminance in cd·m-2;

Eeye,i

is the illuminance in lx at the observer’s eye, height 1,5 m above road level, in the plane normal to the line of sight. The line of sight is 1° below the horizontal;

Θ

is the angle in degrees of arc between the line of sight and the centre of the luminaire;

n

is the number of luminaires in the field of view;

k

is a constant which varies according to the age of the observer. It is conventionally taken as 10, which is applicable for an observer of an age of 23 years. Its value can be derived from the formula (C.3):

⎡ ⎛ A ⎞4 ⎤ k = 9,86 ⎢1 + ⎜ ⎟ ⎥ ⎢⎣ ⎝ 66, 4 ⎠ ⎥⎦ A NOTE

(C.3)

is the age of the observer in years. Equation (C.2) is valid for 1,5° < Θ < 60° (CIE 31-1976).

The effect of the observer’s age on TI is illustrated for a fictitious situation in Figure C.1.

29

Threshold increment, Threshold incrementTI(%)

CIE 115:2010

40,0 35,0 30,0 25,0 20,0 15,0 10,0 5,0 0,0 20

25

30

35

40

45

50

55

60

65

70

75

80

Age (years) 0,5 cd/m LL== 0,5 cd⋅m2-2

Figure C.1.

1,0 cd/m LL== 1,0 cd⋅m2-2

1,5 cd/m LL== 1,5 cd⋅m2-2

The threshold increment TI (fTI) for a fictitious lighting system, each curve representing a different adaptation luminance L (cd·m-2) of the driver. TI increases with the drivers’ age.

ANNEX D: CONTROL OF GLARE IN PEDESTRIAN AND LOW SPEED TRAFFIC AREAS Where visual tasks usually considered for the lighting of roads for motorized traffic (M classes) or conflict areas (C classes) are of importance, the threshold increment (fTI) should be used as an appropriate measure to evaluate the glare experienced. TI can be used to control glare in pedestrian and low speed traffic areas, and limits are specified for the different P lighting classes in Table D.1 Table D.1. Maximum threshold increments for pedestrian and low speed traffic areas. Lighting Class

Threshold Increment (fTI) in %

P1

20

P2

25

P3

25

P4

30

P5

30

P6

35

Alternatively glare in pedestrian and low speed traffic areas may be controlled by not exceeding the luminous intensity limits specified in Table D.2 for luminous intensity classes G1 to G6 as maximum luminous intensities per 1000 lm for different angles of elevation. NOTE This alternative approach may be used in those conflict areas where viewing distances are short and there are multiple observer positions and luminaire orientations.

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CIE 115:2010

Table D.2. Maximum luminous intensities for luminous intensity classes G1 to G6. Luminous Intensity Class

Maximum luminous intensity in cd·klm-1

Other requirements

At 70° and above

At 80° and above

At 90° and above

G1

---

200

50

None

G2

---

150

30

None

G3

---

100

20

None

G4

500

100

10

G5

350

100

10

Luminous intensities above 95° to less than 1 cd·klm-1

G6

350

100