RP 22 96 Tunnel Lighting
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ANWIESNA
RP-22-96
American National Standard Practice for Tunnel Lighting
Prepared by the IESNA Roadway on Tunnels and Underpasses
Suggestions for revisions to this document should be directed to IESNA.
Lighting
Subcommittee
ANSI/IESNA
RP-22-96
Prepared by the IESNA Roadway Lighting Subcommittee Antanas Ketvirtis,
on Tunnels and Underpasses
Subchair
W. Adrian J.C. Bait’ J.A. Bastianpillai J.J. Buraczynski K.A. Burkett V.F. Carney R.A. Catone B.T. Chau D. Chaudhuri V. Cimino P.G. Contos C.W. Craig J.E. Degnan
J. DeVaal Z. Durys G.A. Eslinger C. Goodspeed J.A. Havard H. Kajiyama P.J. Lutkevich W.E. Morehead E. Morel P.A. Mowczan C.A. Oerkvitz CL. Thomas, Jr.
IESNA Roadway Lighting Committee Ian Lewin, Chair -Balu Ananthanarayanan, John J. Mickel, Secretary W. Adrian A.P. Allegretto* J.B. Arens J.D. Armstrong J.C. Bair* J.A. Bastianpillai* P.C. Box R.A. Bradford* R.J. Broadbent* J.J. Buraczynski* K.A. Burkett J.C. Busser E. Cacique* M.G. Canavan V.F. Carney L.A. Casolo, Jr.* R.A. Catone* T.J. Chapman B.T. Chau* D. Chaudhuri* R.B. Chong V. Cimino RD. Clear P.G. Contos V.J. Cartes* C.W. Craig D.L. Crawford* CL. Crouch** W. Daiber J.E. Degnan R.J. Drago* Z. Durys* W.H. Edman** J.W. Edmonds* G.A. Eslinger K. Fairbanks* D.H. Fox*
Vice Chair
M. Freedman D.G. Garner* R. Gibbons* A.S. Gael* C. Goodspeed* W.C. Gungle* R.C. Gupta R.L. Hamm* J.M. Hart G.A. Hauser* J.A. Havard E.O. Heinlein** W.A. Hughes D.E. Husby M.S. Janoff J.E. Jewel1 H. Kajiyama* M.E. Keck D.M. Keith A. Kevirtis AS. Kosiorek* G.S. LaBar* R.C. LeVere C.H. Loch P.J. Lutkevich D. Mace* D.R. Macha* L.J. Maloney* M. Maltezos* S.D. Mathias* G.H. McConnell* J. McCormick SW. McKnight J.F. Meyers D.R. Monahan* R.G. Monsoor S. Moonah*
W.E. Morehead* E. Morel H.D. Mosley** P.A. Mowczan K. Negash* H.A. Odle C.A. Oerkvitz D.W. Okon’ ES. Phillips* G.P. Robinson* A.S. Rose EC. Rowsell P.P. Sabau* N.A. Schiewe R.N. Schwab B.L. Shelby** A.D. Silbige? J-F. Simard* R.L. Sitzema G.E. Smallwood R.E. Stark G.J. Stelzmiller* L.A. Stephens* CL. Thomas, Jr. K.M. Thompson* H.A. Van Dusen R. Vincent V.H. Waight J.D. Walters C.P. Watson G.W. Weist* G. Westergren* R.R. Wylie R.J. Wynn* *Advisory **Honorary
Member Member
ANSI/IESNA
Copyright
1996 by the Illuminating
Engineering
Society of North America.
Approved by the IESNA Board of Directors, May 13, 1996, as a Transaction the Illuminating Engineering Society of North America. A// rights reserved. No part of this publication any electronic retrieval system or otherwise, the IESNA. Published by the Illuminating Engineering Street, New York, New York 10005.
of
may be reproduced in any form, in without prior written permission of Society of North America,
120 Wall
IESNA Standards and Guides are developed through committee consensus and produced by the IESNA Office in New York. Careful attention is given to style and accuracy. If any errors are noted in this document, please forward them to Rita Harrold, Director Educational and Technical Development, at the above address for verification and correction. The IESNA welcomes and urges feedback and comments. Printed in the United States of America.
RF’-22-96
ANSMESNA
RP-22-96
CONTENTS 1.0
Introduction
2.0
Physical Characteristics 2.1 2.2
3.0
Visibility 4.1 4.2 4.3 4.4 4.5
5.0
.1 .l 1 .l 1 .l 2
Tunnel Lighting Needs .................................................................. .2
......... 2 General ......................................................................................................... 2 Geographic Location ............................................................................................. 2 Climatic Conditions ................................................................................................ 2 Tunnel Structure Orientation .................................................................................. .3 Traffic Speed ........................................................................................................ ....................................................................................................... .3 Traffic Volume 3 Materials Used in Tunnel Construction .................................................................. 3 ........................................................................ Divided and Undivided Structures .3 Tunnels with Special Portal Design ......................................................................
at the Tunnel Approach and Portal ................................................................. 4 General .................................................................................................................. Pavement Type at Tunnel Approaches ................................................................. Black Hole Effect ................................................................................................... Black-Out Effect ..................................................................................................... Adaptation Point ....................................................................................................
4 4 4 5 5
Luminance of Tunnel Interior Surfaces .......................................................................... 5 5.1 5.2 5.3
6.0
.................................................................................................
Definition of a Tunnel ............................................................................................ Tunnel Classification. ............................................................................................. 2.2.1 Short Tunnel.. ........................................................................................... 2.2.2 Long Tunnel .............................................................................................. 2.2.3 Divided and Undivided Tunnels .............................................................. 2.2.4 Underpasses and Overpasses .................................................................
Factors Influencing 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9
4.0
................................................. .................... ............................................. 1
.5 Architectural Features of Tunnel Cross Section ................................................... Pavement, Wall, and Ceiling Materials, and Reflective Characteristics ............... .5 5 Wide and Narrow Tunnels .....................................................................................
Lighting Design Criteria ................................................................................................... 6.1 6.2 6.3 6.4
6.5 6.6
General .................................................................................................................. Lighting Requirements.. ......................................................................................... Assessment of the Major Factors Influencing Lighting Design ............................ Method of Determination of Luminance Levels .................................................... Luminance Values in Threshold Zone ....................................................... 6.4.1 6.4.2 Threshold and Transition Zones ............................................................... 6.4.3 Tunnel Interior Zone.. ................................................................................ 6.4.4 Nighttime Luminance ................................................................................ 6.4.5 Non-Roadway Surface Luminances ......................................................... 6.4.6 Uniformity Ratios.. ..................................................................................... Flicker Effect .......... ................................................................................................ Switching Steps in Threshold and Transition Zones. .............................................
5 5 5 .6 .6 6 6 6 6 8 8 9 9
ANSI/IESNA
7.0
Light Application
9 9 9
Symmetrical Light Distribution.. ............................................................................. Asymmetrical Light Distribution-Negative Contrast ............................................ Asymmetrical Light Distribution-Positive Contrast .............................................
.9
Lighting and Electrical Equipment.. ...............................................................................
.9
7.1 7.2 7.3 8.0
Techniques ..........................................................................................
Light Sources ......................................................................................................... 8.1 .I Fluorescent.. ........................................................................................... 8.1.2 Low Pressure Sodium (LPS) ................................................................... 8.1.3 High Pressure Sodium (HPS). ................................................................. 8.1.4 Metal Halide (MH) ................................................................................... 8.1.5 Other Light Sources ............................................................................... Luminaires ........................................................................................................... Electric Power Supply and Distribution .............................................................. Switching and Control ..........................................................................................
8.1
8.2 8.3 8.4
9 10 10 l-0 10 .lO 10 .l 1 11
General ................................................................................................................ Initial Cost ............................................................................................................ Life-Cycle Economic Analysis ............................................................................
11 11 11 .ll
........................................................................................ ............................................................................................................... General Lamp Lumen Depreciation .................................................................................. Luminaire Dirt Depreciation.. ............................................................................... Tunnel Surface Reflectance Depreciation .......................................................... 10.4.1 Selection of Tunnel Surface Reflectance.. .............................................. 10.4.2 Reflectance Depreciation ....................................................................... Luminaire Cleaning and Relamping .................................................................... 10.5.1 Luminaire Cleaning ................................................................................. 10.5.2 Relamping ...............................................................................................
.12 .I2 12 12 .12 12 12 13 13 13
.._...................................................
14
Glossary
.....................................................................................................................................
15
Annex A
Calculation
Annex 6
Method of Computing
Lighting System Economics. ......................................................................................... 9.1 9.2 9.3
Maintenance Considerations
References
...
.........................................................................
Method ...................................................................................................
20
Luminance Levels in the Threshold Zone ....................... .26
RP-22-96
ANSI/IESNA
2.0 PHYSICAL CHARACTERISTICS
1 .O INTRODUCTION 2.1
This standard practice has the objective of providing information to assist engineers and designers in determining lighting needs, recommending solutions, and evaluating resulting visibility at vehicular tunnel approaches and interiors.
2.2
Tunnel Classification
In classifying tunnel structures, two factors should be taken into account: structure length and its geometric alignment (visibility through the structure).
The basic design criteria for tunnel lighting are outlined in Section 6.0 of this document. Tunnels may require considerably different treatment of the threshold zone luminance values, depending on variables such as geographic orientation, geometric design, traffic volume, traffic speed, service levels, light source used, and modes of light application. The lighting designer therefore should consider the factors which affect the visibility conditions as outlined in Section 3.0. Treatment of tunnel portals, wall and ceiling surfaces, and selection of lighting equipment, as well as light sources, maintenance, and lighting economics are also reviewed and assessed in this document. However, special requirements for pedestrians are not addressed in this document.
THRESHOLD ZONE
Definition of a Tunnel
A tunnel is defined as a structure over a roadway which restricts the normal daytime illumination of a roadway section such that the driver’s visibility is substantially diminished (see Figure 1).
This practice is intended also for use by administrators charged with the responsibility of providing a safe visual environment within a tunnel during both daytime and nighttime hours.
APPROACH
RP-22-96
Short Tunnel. A straight tunnel having an 2.2.1 overall length from portal to portal, along the centerline, which is equal to, or less than, the SafeStopping-Sight-Distance (SSSD) is considered to be a short tunnel. See Table 1. 2.2.2 Long Tunnel. A tunnel with an overall length greater than one SSSD, or having an alignment or curvature which prevents motorists from seeing through the structure to the exit end, is considered to be a long tunnel. 2.2.3 Divided and Undivided Tunnels. A structure which consists of two separate enclosures, each designated to accommodate one direction of traffic flow, is considered to be a divided tunnel.
TRANSITION ZONE(S)
INTERIOR ZONE
PORTAL
Figure 1. The primary external and internal areas associated (Formal definitions of each primary area are in the glossary.) .
with and affected by tunnel lighting design.
1
ANSI/IESNA
RP-22-96
3.2
A structure which consists of a common enclosure to accommodate the traffic flow in both directions is considered an undivided tunnel.
Geographic Location
With respect to the geographic location, tunnel lighting design may be affected by the following:
2.2.4 Underpasses and Overpasses. Structures considered to be Underpass or Overpass structures are those in which the length does not exceed one width of the roadway over (or under) which they are constructed. Refer to references 1 and 2 for design information.
l l l
Surrounding land character Type of growth surrounding Solar altitude and azimuth
3.3
tunnel structure
Climatic Conditions
Climatic conditions which influence system design include the following:
3.0 FACTORS INFLUENCING TUNNEL LIGHTING NEEDS
l l l
3.1
General
l l
Ambient luminances of the surfaces adjacent to the tunnel portal within the visual field are the most important factors in determining the threshold zone luminance values. Elements affecting this, and other factors, act as important modifiers to the final lighting design. These modifiers may impact the lighting design levels by as much as *20 percent total. Section 6.0 allows these modifiers to be factored into the final design criteria, but leaves the decision on their relative weight to the lighting designer.
the lighting
Temperature range Humidity levels Seasonal changes in natural growth Presence or absence of snow Atmospheric conditions (such as clouds and haze)
3.4
Tunnel Structure Orientation
The presence of the sun in or near the approach viewing angle of the tunnel portal creates a severe illumination design problem. This occurs with eastwest tunnels at the east portal prior to sunset, and at the west portal for a period after sunrise. It can also occur in north-south tunnels at the north portal, especially during winter months at higher lati-
TABLE 1: AASHTO STOPPING SIGHT DISTANCE (Wet Pavement) Estimated Safe Stopping Sight Distance (SSSD) t 1 Meters Feet I
Traffic Speed (estimated km/h and mph1 Kilometers
Miles per Hour
-per Hour I 50
60 80 90 100 110
I
60 90 140 160 190 220
30 40 50 55 60 65
Refer to American Association of State Highway and Transportation Officials Highways and Streets,” 1990 for accurate calculation of stopping sight distance. tAssumes average prevailing speeds in a straight and level tunnel approach the facility. For other geometric conditions, refer to the AASHTO document.
2
200 300 450 530 620 720
(AASHTO)
roadway
“A Policy on Geometric
Design of
are at, or near, the posted speed limit of
ANSIIIESNA
tudes. If the sun the portal during these orientations, very high, creating
is close to the an approach the luminance a high veiling
viewing angle of to a tunnel with of the sky will be luminance.
The problem can be accentuated by a depressed portal which permits a direct line of sight to the sun at low viewing angles. An example would be a tunnel under a river. Highly reflective surfaces outside of a portal, particularly those with specular characteristics, can also contribute to elevating the luminance of the areas around the portal. High exterior luminances from the sun, sky, or specular surfaces around the portal require high threshold luminances; however, no lighting system can compete directly with the sun. Mitigating factors are natural or artificial structures such as mountains (without snow), trees, and buildings which have low coefficients of reflectance and block the sky from view during the motorist’s approach to the tunnel. These factors are often present in mountainous or urban areas, and their impact on design is discussed further in Section 6.0.
3.5
Traffic Speed
Since the eye adaptation process under dynamic conditions is relatively slow, traffic speed is of great importance in determining the required luminance value in the threshold zone. A motorist approaching a tunnel entrance at a relatively low speed, say 40 km/h (25 mph), and fixating his/her eyes at a distance of 150 m (492 ft.), will have a preadaptation period of 13 seconds before the entry into the tunnel, permitting significantly lower luminance values in the threshold zone. A motorist travelling at 80 km/h (50 mph) will have only 6.5 seconds for eye preadaptation, thus, the demand for eye adaptation will be more severe, and significantly higher luminance values will be required in the threshold zone.
3.6
Traffic Volume
The yearly average number of vehicles that pass through a tunnel within a 24-hour period, the Average Annual Daily Traffic (AADT), is of significance in determining not only tunnel interior luminance levels, but also in quality of lighting, lighting equipment types, and maintenance and operation procedures. When designing a tunnel lighting system, traffic volume, traffic density, vehicle headway, and lane occupancy should be taken into account.
RP-22-96
A high traffic volume also implies a need to maintain the flow of traffic. The perception by the motorist of the presence of light within the tunnel will encourage the motorist to maintain speed. Interior surfaces with high luminances will give motorists the impression of a “bright” tunnel.
3.7
Materials Used in Tunnel Construction
Architectural features of a tunnel approach may have a pronounced effect on the preadaptation process. High retaining walls flanking the approach road, painted black or with concrete darkeners, will enhance eye adjustment. The same types of retaining walls painted white will keep the eye adaptation at a relatively high level, requiring higher levels of surface luminance within the tunnel. Curved portals may permit greater contribution of daylight towards the threshold zone lighting. In designing a lighting system, materials used in the tunnel structure are of considerable importance, particularly with respect to their characteristics of reflectance. For example, tunnel wall surfaces may be finished with untreated rock, raw concrete, epoxy paint, concrete sealer, or glazed ceramic tiles. The maintained reflectance coeff icient of untreated rock would be approximately 7 percent, untreated concrete 10 percent, and glazed tiles in the order of 45-60 percent. The use of these materials will have an effect not only on tunnel luminance calculations, but also on the interreflectance, which influences.the pavement luminance values and luminance uniformity, as well as contrasts.
3.6
Divided and Undivided Structures
Traffic operation in divided and undivided tunnels differs in many respects. Divided tunnels are regarded as offering safer traffic flow. In divided tunnels there is almost no possibility for head-on collisions, and in the case of multi-lane tunnels, the occupancy of lanes is more evenly distributed than in undivided structures. For this reason, the lighting level for the interior zone should be higher in undivided tunnels compared with that of divided tunnels. 3.9
Tunnels with Special Portal Design
Some vehicular tunnel designs incorporate sunscreens, solar galleries, and other similar devices, whereby the daylight is used in reduced intensity as an intermediate level between the outdoor lighting and the tunnel interior. In such situations, the threshold and transition zone luminance levels should be reduced by the steps shown in Figure 2 where the screened daylight area becomes the threshold zone. 3
ANSI/IESNA RP-22-96
I
SECONDS.
Figure 2. Recommended zone inside a tunnel.
0
luminance
2
4
reduction
Caution should be exercised when using sunscreen or solar gallery designs as some may be susceptible to dirt or snow accumulation on the reflective surfaces of the screens, thus creating serious maintenance problems and/or reduction of their effectiveness in regulating intended lighting levels.
4.0 VISIBILITY AT THE TUNNEL APPROACH AND PORTAL 4.1
General
Coordination of the lighting system and the tunnel architectural, structural, and civil designs is essential in order to provide adequate visibility at the
4
6
8
10
12
steps for the threshold
14
16
zone and the transition
entrance of a tunnel. This coordination should occur at the beginning of the project and continue throughout the design process.
4.2
Pavement Type at Tunnel Approaches
Since eye adaptation prior to entering a tunnel interior is affected by the exterior approach road pavement, a dark asphalt surface or darkened concrete will result in a decrease of the required threshold zone luminance.
4.3
“Black Hole” Effect
The black hole effect, due to the perceived difference in the external and internal luminances, occurs when drivers slow down because they do not have sufficient confidence that their path inside the tunnel is clear.
ANSVIESNA RP-22-96
4.4
“Black-Out”
Effect
Motorists entering a tunnel interior at a relatively high speed will require sufficient time for physiological changes to occur within the eye. If the threshold zone is too short, in relation to the speed of travel, the time available (see Figure 2) for eye adaptation may also be too short, resulting in a black-out effect. If the transition zone between threshold and tunnel interior lighting is too short, a screening phenomenon (i.e., a defined and perceptible line of light and dark) detrimental to the driver’s performance will occur.
4.5
Adaptation
Point
An average windshield cut-off angle for a vehicle above the horizontal plane is approximately 22”25”. The distance back from the tunnel portal where the cut-off angle lines up with the top of the tunnel opening height at a driver height of 1.45 m (4.76 ft.), is where the structure opening is the principal feature in the visual field. This location is called the adaptation point and its distance away from the tunnel portal may be deducted from the threshold zone length.
5.0 LUMINANCE OF TUNNEL INTERIOR SURFACES 5.1
The reflectance of the tunnel pavement will have a considerable impact on the amount of light required. The visibility of an object on the pavement will vary with the luminance contrast (see the glossary). Luminance contrast is influenced by the reflectance of the pavement and objects, the directional orientation of the artificial light source, and the amount of interreflected light (see Section 7.0). Cement-concrete pavement has a higher total reflectance factor, but may not enhance contrast because of its predominantly diffuse reflectance characteristics. Smooth black asphalt has a lower total reflectance factor, but may improve contrast due to the presence of some specular reflections.
5.3
The width of the tunnel will influence the amount of interreflection between surfaces and therefore impact the overall pavement luminance. In relatively wide tunnels (three or more travel lanes) with highly reflective surface materials, interreflection may be minimal (less than 10 percent), whereas interreflection in narrow tunnels (one or two travel lanes) may be considerable (up to 50 percent) depending on cleaning. The reflected light, however, can reduce the amount of pavement and object luminance contrast. If the interior surfaces of tunnels are treated with low reflectance materials, or are poorly maintained, interreflection may be negligible.
6.0 LIGHTING DESIGN CRITERIA
Architectural Features of Tunnel Cross-Section 6.1
The tunnel cross-section may be rectangular or horseshoe-shaped, and may include textured or grooved walls. The horseshoe cross-section and textured surfaces assist in controlling noise, and thus, are often recommended by architectslengineers. Different tunnel cross sections influence light interreflection and options for luminaire placement.
5.2
Reflective Characteristics of Pavement, Wall, and Ceiling Materials
It is recommended that wall surfaces be of an easily maintained, highly reflective, nonspecular material having an initial reflectance of at least 50 percent. In tunnels where ceiling reflectance will contribute to the utilization of light, these surfaces should be finished similarly to the walls. For light application techniques not utilizing uplight, ceilings may be unfinished or painted with dark flat paints for ease of maintenance.
Wide and Narrow Tunnels
General
The main objective in tunnel lighting design is to provide a lighting system for a given tunnel which meets the visibility requirements for day and night conditions. The task for a designer is not a simple one, particularly in the case of a new tunnel, when often only partial information about the portal and about the approach roads is available. Procedures for tunnel lighting design and the design criteria included in this chapter are based not only on theoretical considerations, but also on information drawn from practical experience and engineering judgment.
6.2
Lighting Requirements
Whether daytime lighting is to be provided in tunnels of different lengths will depend on a number of factors. A summary of these conditions, including recommendations for the threshold zone of the tunnel, is included in. Figure 2, Figure 3, Table 2, and
Table 3. 5
ANSI/IESNA
RP-22-96
6.4
Methods of Determination Luminance Levels
of
This section discusses the methods appropriate for the determination of luminance values within the tunnel. A calculation method for use in predicting the performance of a particular lighting system is found in Annex A. 6.4.1 Luminance Values in Threshold Zone. The threshold zone luminance (Lth) can be determined using the following procedures: l l l
l l
Determine maintenance factor. Determine percent of Lth from Table 2. Determine the tunnel scene closest to that of the design tunnel (Figure 3). Determine the traffic speed and orientation. Read the appropriate luminance value from Table 3 and factor by the percent found in
Table 2. l
Adjust the value obtained for modifications required by the factors outlined in Section 3.0 (maximum adjustment approximate *20 percent).
Included in Annex B is the expanded method of determining threshold zone luminance by determining the equivalent veiling luminance (Lseq).
Figure 3. Various tunnel approach scenes prepared by the CIE Committee on Tunnel Lighting representing eight different luminance settings.
6.3
Assessment of Major Factors Influencing Lighting Design Criteria
In Section 3.0, the major factors affecting lighting requirements in the tunnel entrance zone and in its interior were discussed. Due to the complexity of the conditions it is impossible to mathematically determine exact design luminance values in the threshold and interior zones. The luminance values recommended in Table 3 serve as base values for the tunnel threshold zones. Adjustments to these values are required by taking into consideration the factors outlined in Section 3.0. for the tunnel being designed. Changes to the base values derived from the methods given in Section 6.4 may be as large as *20 percent depending on the specific conditions.
6
6.4.2 Threshold and Transition Zones. A sample for the reduction of luminance levels in the threshold and in the transition zones is shown in Figure 2. The recommended length of each of these zones should be approximately one safe-stopping-~ sight-distance (SSSD). 6.4.3 Tunnel interior Zone. The tunnel interior zone is the portion of the tunnel where the motorist’s vision has adapted to a low luminance environment. Luminance levels in the tunnel interior for daytime conditions should be as outlined in
Table 4. 6.4.4 Nighttime Luminance. During nighttime the motorist’s eyes are adapted to the low exterior luminance; therefore, a nighttime pavement luminance of 2.5 cd/m2 minimum is recommended for the entire length of the tunnel. (This luminance value has been derived by consensus among experts.‘) The approach and exit roadways should have a luminance level of no less than one-third the tunnel interior level for a distance of a SSSD.
TABLE 2 Adjustment Factors for Pavement Luminance in Threshold (Lth) (Adapted from CIE 68, Table 5.3 Reference 3) TABLE 2
WALL REFLECTANCE
Low Wail Reflectance High Wall Reflectance
’ light Traffic Volume < 75,000 AADT Heavy Tmftk Volume > 75,000 AADT
WALL REFLECTANCE
< 30% > 30%
Table 3 Recommended Daytime Maintained Average Pavement Luminance Levels in the Threshold Zone of Vehicular Tunnels (Lth) Approach
Characteristics*
Traffic
Driver Direction
Speed
km/h
mph
North
I
East-West
I
South
cd/m2 100
60
250
310
370
80
50
220
260
320
60
40
180
220
270
Urban T&
100
60
320
280
310
Scene 4.6.6
80
60
280
240
270
60
40
230
200
220
Scene 1.2.3
I Mountain
Tunnel
Scene 7.8
The figures shown in this Table should be regarded as the basic approximate values of the luminance (Lth) only utilizing an SRN of 4.7 (Refer to Annex 6 for method). The final luminance levels should be determined after the modifying factors listed in Section 3.0 are taken into consideration. *See Figure 3.
7
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RP-22-96
TABLE 4 Daytime Interior Zone Average Luminance Recommended from the Road Interior zone average road surface luminance in cd/m* Traffic Flow Traffic Speed
100 km/h (60 mph) 80 km/h (50 mph) 60 km/h (40 mph)
5 2,400 AADT
Low
Medium > 2,400 AADT < 24,000 AADT
Heavy 2 24000 AADT
6 4 3
8 6 4
10
6.4.5 Non-Roadway Surface Luminances. In general, interior surfaces with high luminances will decrease the black hole effect, improve the visibility of objects seen by contrast, and improve the motorist’s perception of the presence of light in the tunnel. Tunnel interiors are composed of roadway shoulders, walls, and ceilings, in addition to the roadway pavement. Luminance requirements for non-roadway surfaces vary with tunnel geometry and architecture, traffic volume, light application techniques, and other factors as identified in Section 4.0 and Section 5.0. However, higher interior surface luminance does not always improve visibility. Some wall luminance, however, is always necessary. The lower part of the tunnel walls, up to 3 meters (10 ft.) above the roadway shoulder, should have a minimum luminance of one-third of the roadway level. Greater luminance, up to the full pavement luminance, is desirable if a wall forms a major portion of the viewable background. The most common example is the outer curve wall and roadway shoulder of a curved tunnel. Other geometries, architecture, or tunnel usage (such as bicyclists) may require improving wall luminance as well. Ceiling luminance may be beneficial in tunnels where the threshold slopes downhill, or where the tunnel is level and the approach to the threshold is uphill. However, the luminance of the luminaires can define the ceiling geometry and effectively create a luminous surface. Additionally, the motorist’s attention is mostly directed towards the roadway surface and evasive routes, so the ceiling luminance is less critical. 8
a 6
Maintenance aspects should also be considered when targeting an improved luminance value for a particular surface. Some surfaces, such as shoulders, may accumulate prohibitive amounts of dirt; others, such as high or uneven ceilings, may be difficult to clean. 6.4.6 Uniformity Ratios. Uniform luminance of tunnel interior surfaces is necessary to assure adequate adaptation to tunnel luminances. Individual luminaires with set candela distribution patterns give variations in luminance levels depending on the pattern and distance from the luminaire. The uniformity ratio tolerances relative to the values in Figure 2, are 2 to 1, average-to-minimum; and 3.5 to 1 maximum-to-minimum. (These uniformity ratios have been derived by consensus among experts.) In order to *avoid glare from the lighting system, which would in turn impact the visibility of an object within the tunnel, the veiling luminances ratio should be less than 0.3 to 1 and as defined in ANSI/IESNA RP-8:’ These tolerances are applicable across all travel lanes in a single direction and are to be calculated across multiple lanes in a multi-lane tunnel.
Figure 2 shows average luminance levels decreasing smoothly throughout the transition zone(s), and into the interior zone. It is intended that the luminance decrease with smooth transitions. The curve represents an average pavement luminance in various zones at any distance inside the tunnel. For a given distance, the luminance along a section of pavement must meet the uniformity requirements for the average light level determined by Figure 2.
ANSI/IESNA RP-22-96
These uniformity ratios are applicable to the roadway pavement and to the portion of the non-roadway surfaces requiring luminance. It is not practical to account for lamp burnouts when designing for uniformity, and recommendations should be made to the tunnel operator regarding spot relamping.
6.5
Flicker Effect
In the interior of a lighted tunnel where luminaires or their reflected images are in full or partial view of the vehicle occupants, the stroboscopic effect of passing closely spaced light sources may produce undesirable behavioral sensations.
I2
7.0 LIGHT APPLICATION TECHNIQUES 7.1
Symmetrical Light Distribution
Symmetrical light distributions used in tunnel lighting design will produce a uniform luminance throughout the tunnel interior, particularly when linear sources are used. However, relatively low contrast values will be generated.
7.2
Asymmetrical Light DistributionNegative Contrast system
is also known
as Counter-
7
6
91011I21
CYCLES PER SECOND
beam Lighting (CBL). Light is predominantly distributed toward the driver providing high pavement luminance and low object luminance creating negative contrast.
7.3
Asymmetrical Light DistributionPositive Contrast
The ALD-PC system, also known as Pro-beam Lighting (PBL), is similar to that of the Counterbeam light application technique, except the direction of the main beam of light is in the direction of the traffic flow. This method provides high object luminance and low pavement luminance creating positive contrast.
8.0 LIGHTING AND ELECTRICAL EQUIPMENT 8.1
Light Sources
Fluorescent, Low Pressure Sodium (LPS), Metal Halide, and High Pressure Sodium (HPS) lamps are the light sources often used for tunnel lighting installations. The following factors affect the selection of light sources for tunnel lighting: l l l l l
The ALD-NC
6
Figure 4. The stroboscopic effect produced when a motorist passes closely-spaced light sources in a tunnel can result in undesirable behavior and sensations.
Switching Steps in Threshold and Transition Zones
Tunnel threshold and its interior lighting requirements vary during daily operation as a result of the changes in external luminances created by weather conditions and/or the position of the sun. For the purpose of maintaining luminance ratios between exterior and interior surfaces during varying ambient light conditions, switching steps are often used. This is achieved by arranging the luminaire numbers and lamp sizes within each switching cycle, as well as the circuitry design of the system. The switching steps are normally controlled by appropriate photocontrols. Switching from full daytime levels to nighttime levels should be moderately stepped to avoid abrupt changes in illumination.
5
WMINAIRE
Figure 4 illustrates the range of luminaire cycles per second that are considered to produce the disturbing effects. It is recommended that the designer avoid luminaire spacing within the annoyance range shown (5 to 10 cycles per second). However, the effect of flicker in practice may cause negative effects on a driver’s performance. 6.6
3 4
l
Efficacy Lamp lumen output (lamp size) Life Lamp lumen depreciation Ambient temperature Cost (lamp and lu’minaire)
9
ANWESNA RP-22-96
Restrike time Luminaire light distribution l Physical size (lamp and luminaire) . Physical durability (lamp and luminaire). l Color temperature l l
The advantages and disadvantages of the various viable sources are discussed in the following paragraphs. 8.1.1 Fluorescent. Fluorescent lamps are frequently used for the tunnel interior zones, where lower illumination levels are required. They are often used in conjunction with other light sources which provide the higher illumination levels required in threshold and transition zones. The advantages of fluorescent lamps include: (1) instant restrike in the event of momentary power interruption, (2) linear source, which can provide continuous lighting, eliminating the concern for flicker effect, (3) low lamp cost, and (4) availability of various lamp color temperatures with high color rendering indices. The disadvantages include: (1) possible large lamp size, (2) potential lower lamp efficacy, (3) minimal control of luminaire light distribution, (4) reduced lumen output at lower temperatures, and (5) difficulty of maintaining the luminaire dust-tight and water-tight for large enclosures. 8.1.2 Low Pressure Sodium (LPS). Low pressure sodium lamps have very high efficacy and are frequently used in conjunction with other sources to provide the high illumination levels required in threshold and transition zones. Lower wattage LPS sources can be also used in interior zones. The advantages include: (1) relatively short restrike in the event of momentary power interruption, (2) linear source (in larger size lamps), which may reduce the concern for flicker effect, (3) high efficacy, and (4) minimal or no lamp lumen depreciation over life (at the expense of increased power consumption over the same period). The disadvantages include: (1) high lamp replacement cost, (2) possible large luminaire size, (3) shorter lamp life than HPS lamps, (4) minimal control of light distribution, (5) poor Color Rendering Index (CRI), and (6) difficulty of maintaining the luminaire dust-tight and water-tight for larger enclosures. 10
8.1.3 High Pressure Sodium (HPS). High pressure sodium lamps have a wide selection of lamp sizes, increased life ratings, compact size, and are easily optically controlled. The advantages include: (1) high lamp efficacy, (2) excellent luminaire light control, resulting in high luminaire efficiency, and (3) good lamp life and minimal lumen depreciation. The disadvantages include: (1) required restrike time in the event of momentary power interruption (or higher cost for dual arc tube lamps), (2) small luminaire size, which may require that flicker effect be considered, (3) careful luminaire design and placement to eliminate high brightness and resultant discomfort and/or disability glare problems, as well as non-uniform wall brightness and/or striations, and (4) potential low Color Rendering Index (CRI). 8.1.4 Metal Halide (MH). Metal Halide lamps also have a wide selection of lamp sizes, good lamp life, compact size, and are easily optically controlled. The primary advantage of metal halide lamps is their color. Various lamp color temperatures are available with a high Color Rendering Index (CRI). The disadvantages include: (1) required restrike time in the event of momentary power interruption, (2) small luminaire size, which may require that flicker effect be considered, (3) careful luminaire design and placement to eliminate high brightness and resultant discomfort and/or disability glare problems as well as non-uniform wall brightness and/or striations, (4) lower efficacy than HPS lamps, and (5) risk of lamp rupture at end of life if operated continuously with no occasional shutdown. 8.15 Other Light Sources. It is rare that an alternate less efficient light source, other than those discussed above, would be used today in the design of either a new lighting system or a replacement system. As new light sources are developed (e.g., sulfur or induction lamps) the available options will grow.
8.2
Luminaires
Tunnel lighting luminaires must be ruggedly construtted to withstand the harsh environment found in all tunnels. Vibration, air turbulence caused by
ANSIIIESNA RP-22-96
vehicles, climates), industrial equipment luminaires
exhaust fumes, road dirt, salt (in some and the periodic washing of tunnels with detergents and high pressure spray are some of the conditions to which are exposed.
The following are factors that must be evaluated the design, selection, installation, and testing tunnel lighting equipment:
9.0 LIGHTING SYSTEM ECONOMICS
9.1
Lighting system economic following major aspects:
in of
l
Prevention of vapor, dust, and water jet spray from entering into the luminaires. l Ease of cleaning, relamping, and replacement of parts. 0 Resistance to corrosion and reactions to dissimilar materials (e.g. concrete). l Physical strength sufficient to prevent warping, twisting, or deforming during installation or servicing. l Highest and lowest ambient operating temperature within the tunnel. l Luminaires which permit specific directional light control, resulting in improved contrast and overall visibility conditions. l
8.3
Electric Power Supply and Distribution
It is important that the tunnel lighting power supply be highly reliable. It is recommended that primary feeders be duplicated and originate from different segments of the power network to minimize the possibility of power supply interruption. Lighting circuits should be divided between the primary sources or configured to provide an equivalent level of redundancy. Consideration should be given to the installation of an emergency power supply to assure essential lighting services.
8.4
Switching and Control
In order to maintain the desired ratio between the exterior luminance level and the threshold zone luminance level, step switching is normally provided to vary the light output of the lighting system. Step switching can be controlled by a set of electronic photocontrols that monitor outdoor light at the tunnel entrance.
l l l l l
analysis consists of the
Selected lighting level Type of light source Quality of lighting equipment Method of equipment installation Maintenance and operation procedures Cost of energy
In the assessment of lighting system economics, initial cost is only one factor to be considered. Typically a more in-depth analysis is involved.
9.2
Initial Cost
The initial cost of the lighting system installation normally includes the equipment cost and the labor cost for installation. In comparing the cost of the lighting systems which employ different equipment (lamps, luminaires), initial capital investment does not provide complete information on the relative system cost. In fact, the initial cost is often misleading for it does not take into consideration such important factors as lamp cost, life, and efficacy. Also, the initial costs do not reflect the maintenance and operation costs, and thus may create a false impression in the process of selecting a lighting system for a given tunnel.
9.3
Life-Cycle Economic Analysis
For a more accurate cost comparison between different lighting systems, an economic analysis based on life-cycle should be used. Such analysis takes into consideration not only the capital investment, but also such factors as: l l l l
Programmable control systems are also available which can result in better coordinated visibility under varying luminance conditions. By monitoring interior tunnel luminances and exterior luminances, and energizing only the luminaires needed, energy consumption can be reduced. This monitoring can also make adjustments for maintenance factors.
General
l
Lamp replacement Energy cost Maintenance and operation expenses Equipment replacement caused by traffic accidents Interest on the capital investment
Numerous-computer programs are available to quickly analyze the life-cycle cost. However, the accuracy of the results will depend on the accuracy of the input data. 11
ANSI/IESNA RP-22-96
10.0 MAINTENANCE CONSIDERATIONS 10.1
General
When planning and designing a tunnel lighting system, the engineers and designers should take into consideration all matters concerning maintenance. A good lighting system is one which not only provides acceptable initial results, but which also enables the maintenance staff to keep system, performance in good condition throughout the expected equipment life. In selecting the equipment, designers should consider its capability to withstand washing by applying high pressure spray and mechanical brushes. Repair of the luminaire components must be accomplished with minimal time spent in the tunnel. Some types of luminaires may be prone to premature failure due to their inability to maintain water tightness and dust tightness, features required in the tunnel environment. Materials used in the manufacturing of the luminaire are of specific importance. Aluminum and carbon steel components exposed to moisture and chemicals may allow galvanic reactions that cause early deterioration of the equipment. The luminaire materials and finish, therefore, should be carefully considered when selecting equipment for tunnel applications. The recommended luminance levels in Table 3 represent the lowest-in-service values that should be maintained throughout the operating life of the system. Therefore, the initial luminance figures should be higher to compensate for Lamp Lumen Depreciation (LLD), Luminaire Dirt Depreciation (LDD), and the tunnel surface (wall and ceiling) reflectance depreciation.
10.2
Lamp Lumen Depreciation
The LLD factor will depend on the type of light source used for the tunnel lighting. Lumen output characteristics for the different lamps (fluorescent, HPS, MH) vary due to aging.
10.3
Luminaire Dirt Depreciation
The LDD factor relates to the depreciation of luminaire lumen output due to dirt deposits on lenses or refractors and dirt on reflectors. LDD must be considered in calculating maintained luminance values specified for the service life of the lighting system. Details about LDD can be found in the IESNA Lighting Handbook, 8th edition and in ANSI/IESNA RP-8.’ 12
The value of the LDD factor is dependent in inverse proportion to the owner’s investment in quality of material and manufacture of luminaires, and to commitment to regular cleaning of glassware/lenses and reflectors. Decisions about LDD factor value (and its relation to the number of fixtures required to meet maintained service levels) and the commitment of resources to regular maintenance should be considered in life-cycle cost analysis as discussed in Section 9.0.
10.4
Tunnel Surface Reflectance Depreciation
10.4.1 Selection of Tunnel Surface Reflectance. Selection of tunnel surface reflectance has a significant impact upon ‘effectiveness of light fixtures in meeting the lighting design criteria. For new tunnels, the lighting designer should participate at the earliest possible time with the owner/architect/structural engineer in selecting the material, finish, and color of tunnel surfaces. This should include the color and, if possible, the physical configuration of walls, ceilings, and portal area. For example, a large low reflectance portal area with high reflectance tunnel interior surfaces can significantly reduce the installation and annual operating cost of lighting required in the threshold zone. For existing tunnels requiring retrofit or reconstructed lighting, consideration should be given to treatment of tunnel walls, especially at the portal or in the threshold zone as part of the lighting project design. Life-cycle economic analysis may reflect long-term savings when appropriate treatment is included. The selection of tunnel surfaces as just discussed should include the specific determination of the reflectance characteristics and reflectance factor. Reflectance characteristics (specular, diffuse, and others) will have significant effect on the effective use of light. 10.4.2 Reflectance Depreciation. Tunnel surfaces will collect dirt, soot, grime, and moisture deposits from vehicle exhaust and atmospheric and subterranean causes. This will result in depreciation of the surface reflectance utilized in the lighting design for the original surface. This should be taken into consideration for calculations utilizing surface reflectances. Also, the lighting designer should determine and influence, if possible, the cleaning schedule and methods the owner plans to use for periodically restoring tunnel surface reflectivity.
ANSI/IESNA RP-22-96
10.5
Luminaire Cleaning and Relamping
Prevention of accidents in tunnels and the potential secondary effect of explosion, fire, or noxious fumes is particularly dependent on maintenance of good lighting and visibility. Maintenance of lighting fixtures in tunnels usually requires lane closures which a well developed cleaning and relamping schedule should minimize. 10.5.1 Luminaife Cleaning. Regular cleaning of refractors, lenses, and reflectors is particularly important in tunnels because these components are constantly subjected to atmospheric pollutants. Periodic cleaning of both external and internal surfaces is required. The internal cleaning requirements will vary depending on fixture specifications. Proposed cleaning schedules and the initial
cost of higher quality fixtures should be included in the life-cycle economic analysis discussed in Section 9.0. Cleaning schedules should be coordinated with relamping schedules as much as possible to minimize lane closures. 10.5.2 Relamping. Consideration of group relamping is more critical in tunnel lighting maintenance programs than for most other lighting systems because of traffic restrictions required in tunnels. Easy, quick relamping (as well as internal cleaning) is affected by the construction, latching, and accessibility of fixtures. These factors should be thoroughly considered in design. Poor designs relative to location, accessibility to the fixture, or ability of workmen (with gloves) to open, service, and close fixtures will significantly affect operating costs which should be considered in Section 9.0.
13
ANSIIIESNA
RP-22-96
References (These references are not part of the American National Standard ANSI/IESNA RP-22-1996). National Standard Practice for 1. American Roadway Lighting, RP-8-83. New York: Illuminating Engineering Society of North America, 1983 (Reaffirmed 1993). 2. “An Informational Guide for Roadway Lighting” Code G-5, American Association of State Highway and Transportation Officials (AASHTO), 444 N. Capital Street, N.W., Suite 225, Washington, DC 20001, 1984. 3. “Guide for the Lighting of Road Tunnels and Underpasses.” International Commission on Illumination, Publication CIE No. 88, 1990.* 4. “Tunnel Entrance Lighting: A Survey of Fundamentals for Determining the Luminance in the Threshold Zone.” CIE Publication No. 61, 1984.* 5. “Guide de I’Eclairage des Tunnels.” Ministere de I’Urbanisme, du Logement et des Transports. (CETU-LYON-FRANCE-MAI), 1985. 6. “Code of Practice for the Lighting of Tunnels.” British Standard Institution, BS5489 Part 7. Beleuchtung Strassen tunnels, 7. “Offentliche Galeries und Unterfiirungen.” Leitsatze der Schweizerische Lichttechuischen Gesellschaft (SLG), SN 418915, 1983. Luminance when 8. Adrian, W.K. “Adaptation Approaching a Tunnel in Daytime.” Lighting Research and Technology, No. 3-1987. Lighting, A Proven 9. Blaser, P. “Counterbeam Alternative for the Lighting of the Entrance Zone of Road Tunnels.” TRB National Conference, Washington, DC, 1990. 10. Schreuder, D.A. Dr. “Practical Determination of Tunnel Entrance Lighting Needs.” TRB National Conference, Washington, DC, 1991. F. and Peviser, 11. Novellas, Method for Road Tunnels.” 2, 1985.*
J. “New Lighting CIE Journal 4, No.
12. Ketvirtis A., P. Eng. FIES. “Visibility Study for Long Vehicular Tunnels.” Journal of the IESNA, Jan. 1975. 14
A., P. Eng. FIES. “Counterbeam 13. Ketvirtis Lighting offers Cost-effective Tunnel Illumination.” Toronto: Electrical Systems Engineer, Spring 1990. 14. Walthert, national 1977b.
R. “Tunnel Lighting Lighting Review,
Systems.” InterVol. 4, p. 112,
W. 15. Gallati, E., Muller, E. and Riemenschneider, “Lighting Values in the Access-Entrance-Zone of a Tunnel.” CIE 20th Session, 1983.* 16. Narisada, K. “Latest Research in Tunnel Lighting in Japan.” Highway Research Circular No. 137, TRB, 1972. 17. Rinalducci,
E. “Transitional Tunnel Lighting.” TRB, 1972.
Adaptation
in
18. Zwahlen,
H.T. “Driver’s Eye Scanning Behaviour of Tunnel Approaches.” Conf. on Eye Movement and Psychological Process, U.S. Army HEL, Monterey, CA, 1977.
Basics to 19. Adrian and Fleming. “Psychological the Lighting Levels in the Transition Zone of Tunnels.” LRI Research Project 88 SPL REF3, Feb.’ 1990. R. V. “Luminance 20. Lewin, I. and Heinisch, Calculations for Tunnel Lighting Systems.” Journal of the IESNA, Winter 1988, pp. 74-79. I. and Heinisch, R. V. “Further 21. Lewin, Developments in Tunnel Lighting Computations.” Journal of the IESNA, Winter 1991, pp. 100-107. for .Quality 22. Committee on Recommendations and Quantity of Illumination of the IESNA. 1973. RQQ Report no. 5. “The Predetermination of Contrast Rendition Factors for the Calculation of Equivalent Sphere Illumination.” Journal of the IESNA, Vol. 2, No. 2, p. 149, January 1973. 23. Adrian, W. Lighting pp. 151-159.
Res. Technol.,
14, 1982,
24. Nakamichi, F., Narisada, K., and Yoshikawa K. Journal Illuminating Engineering Institute of Japan, Vol. 54, No. 10, 1967, pp. 566-581.
*CIE Publications may be ordered from the United States National Committee of CIE, c/o T. Lemons, TLA Lighting Consultants, Inc., 7 Pond Street, Salem, MA 01970-4819.
ANSI/IESNA RP-22-96
candlepower,
Glossary
candelas. (This glossary is not part of the American Standard ANSVIESNA RP-22-1996.)
National
candlepower
accommodation
the process by which the eye changes focus from one distance to another.
adaptation the process by which the visual system becomes accustomed to more or less light or light of a different color than it was exposed to during an immediately preceding period. It results in a change in the sensitivity of the eye to light. approach the external roadway area leading to the tunnel.
ballast a device used with an electric discharge lamp to obtain the necessary circuit conditions [voltage, current, and waveform] for starting and operating. bidirectional reflectance-distribution function, BRDF the ratio of the differential luminance of a ray reflected in a given direction to the differential luminous flux density incident from a given direction of incidence, which produces it.
brightness
see luminance
and subjective
bright-
ness.
candela, cd the SI unit of luminous candela is one lumen per steradian. dle. (See Figure below.)
cp luminous intensity expressed in It is no indication of the total light output.
intensity. One Formerly can-
distribution curve a curve, generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center. central [foveal] vision the seeing of objects in the central or fovea1 part of the visual field, approximately two degrees in diameter. It permits seeing much finer detail than does peripheral vision. Color
Rendering
Index,
CRI measure
of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature.
contrast sensitivity
the ability to detect the presence of luminance differences. Quantitatively, it is equal to the reciprocal of the contrast threshold.
contrast see luminance contrast. contrast threshold the minimal perceptible contrast for a given state of adaptation of the eye. It also is defined as the luminance contrast detectable during some specific fraction of the times it is presented to an observer, usually 50 percent. diffuse reflectance
the ratio of the flux leaving a surface or medium by diffuse reflection to the incident flux.
diffuser a devise to redirect or scatter the light from a source, primarily by the process of diffuse transmission. directional reflectance coefficient the reflectance in a particular direction for incident ray leaving a direction of incidence defined by angles p and y. Also called bidirectional reflectance-distribution function. candela per square meter, cd/m* the SI unit of
disability
glare glare resulting in reduced visual performance and visibility. It often is accompanied by discomfort. See veiling luminance.
luminance equal to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square meter or the average luminance of any surface emitting or reflecting light at that rate. The unit is sometimes called a nit.
discomfort
glare glare producing discomfort. It does not necessarily interfere with visual performance or visibility. 15
ANSI/IESNA
RP-22-96
equivalent luminous intensity [of an extended source at a specified distance] the intensity of a point source which would produce the same illuminance at that distance. Formerly, apparent luminous intensity of an extended source.
intensity a shortening of the terms luminous intensity and radiant intensity. Often misused for the level of illumination or illuminance. interior
zone area within
adaptation
the tunnel has been completed.
after eye
footcandle, fc the unit of illuminance
when the foot is taken as the unit of length. It is the illuminance on a surface one square foot in area on which there is a uniformly distributed flux of one lumen, or the illuminance produced on a surface, all points of which are at a distance of one foot from a directionally uniform point source of one candela.
footlambert,
fL a unit of luminance [photometric brightness] equal to l/n candela per square foot, or to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot, or to the average luminance of any surface emitting or reflecting light at that rate. Use of this unit is deprecated. glare the sensation produced
by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance , discomfort, or loss in visual performance and visibility. See disability glare, discom-
isocandela
line a line plotted on any appropriate
coordinates source of same. For in a closed illuminance
to show directions in space, about a light in which the candlepower is the a complete exploration the line always curve. A series of such lines for various values is called an isolux diagram.
isolux line one plotted on any appropriate coordinates to show all the points on a surface where the illuminance is the same. For a complete exploration the line is a closed curve. A series of such lines for various illuminance values is called an isolux diagram. isoluminance line a line plotted on any appropriate set of coordinates to show all the points on a surface where the luminance is the same. A series of such lines for various luminance values is called an isolumiriance diagram.
fort glare.
lamp a generic term for an artificial source of light.
illuminance,
lamp lumen depreciation factor, LLD the multiplier to be used in calculations to relate the initial rated output of light sources to the anticipated minimum rated output based on relamping program to be used.
E = d@/dA the density of the luminous flux incident on a surface; it is the quotient of the luminous flux by the area of the surface when the latter is uniformly illuminated. illuminance [lux or footcandle] meter an instrument for measuring the illuminance on a plane. Instruments which accurately respond to more than one spectral distribution are color corrected, i.e., the spectral response is balanced to V[3L] or V’[h]. Instruments which accurately respond to more than one spatial distribution of incident flux are cosine corrected, i.e., the response to a source of unit luminous intensity, illuminating the detector from a fixed distance and from different directions decreases as the cosine of the angle between the incident direction and the normal to the detector surface. The instrument is comprised of some form of photodetector, with or without a filter, driving a digital or analog readout through appropriate circuitry. illumination
the being illuminated. density of luminous and such use is to 16
act of illuminating or state of This term has been used for flux on a surface [illuminance] be deprecated.
light center [of a lamp] the center of the smallest sphere that would completely contain the light emitting element of the lamp. light center length [of a lamp] the distance from the light center to a specified the lamp.
reference
point on
light loss factor, LLF a factor used in calculating illuminance or luminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmospheric conditions. Formerly called maintenance factor.
lumen, Im SI unit of luminous flux. Radiometrically, it is determined’from the radiant power. Photometrically, it is the luminous flux emitted within a
ANSIIIESNA
RP-22-96
unit solid angle [one steradian] by a point source having a uniform luminous intensity of one candela.
luminaire a complete lighting unit consisting of a lamp or lamps together with parts designed distribute the light, to position and protect the lamps and to connect the lamps to the power supply. luminaire dirt depreciation factor, LDD the multiplier to be used in the illuminance or luminance calculations to relate the initial illuminance or luminance provided by clean, new luminaires to the reduced illuminance or luminance that they will provide due to dirt collection on the luminaires at the time at which it is anticipated that the cleaning procedures will be instituted. luminance, L = dW/(dw dA co&) [in a direction and at a point of real or imaginary surface] the quotient of the luminous flux at an element of the surface surrounding the point, and propagated in directions defined by an elementary cone containing the given direction, by the product of the solid angle of the cone and the area of the orthogonal projection of the element of the surface on a plane perpendicular to the given direction. The luminous flux may be leaving, passing through, and/or arriving at the surface. Formerly, “photometric brightness.”
Note: in common usage the term “brightness” usually refers to the strength of the sensation which results from viewing surfaces or spaces from which light comes to the eye. This sensation is determined in part by the definitely measurable luminance defined above and in part by conditions of observation such as the state of adaptation of the eye. In much of the literature, the term brightness, used alone, refers to both luminance and sensation. The context usually indicates which meaning is intended. Previous usage notwithstanding, neither the term “brightness“ nor the term “photometric brightness” should be used to denote the concept of luminance. luminance contrast the relationship between the luminances of an object and its immediate background. It is equal to [L1-Lz]/L,, [LrL,]/L,, or AL/L, where L, and L2 are the luminances of the background and object, respectively. The form of the equation must be specified. The ratio AL/L, is known as Weber’s fraction.
By introducing the concept of luminous intensity, luminance may be expressed as L = dl/(dA ~093). Here, luminance at a point of a surface in a direction is interpreted as the quotient of luminous intensity in the given direction produced by an element of the surface surrounding the point by the area of the orthogonal projection of the element of surface on a plane perpendicular of the given direction. [Luminance may be measured at a receiving surface by using L = dE/(dA case). This value may be less than the luminance of the emitting surface due to the attenuation of the transmitting media.]
Note: see last paragraph of the note under luminance. Because of the relationship among luminance, illuminance, and reflectance when only reflecting surfaces are involved. Thus, contrast is
equal to ~I-P~IIPI or [P~-PIIIPI~where PI and p2 are the reflectances of the background and object, respectively. This method of computing contrast holds only for perfectly diffusing surfaces; for other surfaces it is only an approximation unless the angles of incidence and view are taken into consideration. 17
ANSMESNA
RP-22-96
luminous efficacy of a source of light the quotient of the total luminous flux emitted by the total lamp power input. It is expressed in lumens per watt.
degree horizontal end [street side] of the luminaire clockwise is a positive angle. See rotation and tilt.
photometric
brightness
a term formerly used for
luminance.
luminous flux, cpthe time rate of flow of light. luminous
flux density
at a surface, dcp/dA the
luminous flux per unit area at a point on a surface.
Note: this need not be a physical surface; equally well be a mathematical plane.
it may
point of fixation a point or object in the visual field at which the eyes look and upon which they are focused. portal the plane of entrance into the tunnel. primary line of sight the line connecting
luminous
intensity,
I = dq/do the luminous
flux per unit solid angle in a specific direction. Hence, it is the luminous flux on a small surface normal to that direction,
dians]
divided
by the solid
angle
[in stera-
that the surface
subtends at the source. a solid angle must have a point as its apex: the definition of the luminous intensity, therefore, applies strictly to a point source. In practice, however, light emanating from a source whose dimensions are negligible .in comparison with the distance from which it is observed may be considered as coming from a point. For extended sources, see equivalent luminous
of observation
the point
and the point of fixation.
R-table a table for a particular pavement type which provides reduced luminance coefficients in terms of the variable j3 and tarry.
Note: mathematically,
intensity. Iux, lx the SI unit of illuminance.
It is the illuminance on a surface one square meter in area on which there is uniformly distributed flux of one lumen, or the illuminance produced at a surface all points of which are at a distance of one meter from a uniform point source of one candela.
maintenance factor, MF a factor formerly used to denote the ratio of the illuminance on a given area after a period of time to the initial illuminance of the same area. See light loss factor. mean lamp lumens the mean lumen output of a lamp is calculated by determining the area beneath the lumen maintenance characteristic curve of that source over a given period of time and dividing that area by the time period in hours.
reaction time the interval between the beginning of a stimulus and the beginning of the response of an observer. reduced luminance
coefficient, r the value at a point on the pavement defined by angles j3 and y which when multiplied by the appropriate luminous intensity from a luminaire and divided by the square of the mounting height, will yield the pavement luminance at that point produced by the luminaire. reference line either of two radial lines where the surface of the cone of maximum candlepower is intersected by a vertical plane parallel to the curb line and passing through the light center of the luminaire. reflectance of a surface or medium the ratio of the reflected flux to the incident flux. Note: measured values of reflectance depend upon the angles of incidence and view, and on the spectral character of the incident flux. Because of this dependence, the angles of incidence and view, and the spectral characteristics of the source be specified.
mounting
reflector a device used to redirect the luminous flux from a source by the process of reflection.
orientation
refractor a device used to redirect the luminous flux from a source, primarily by the process of refraction.
height, MH the vertical distance between the roadway surface and the center of the apparent light source of the luminaire.
the angular position of the luminaire around an axis through the light center and along the O-180 degree vertical angle. When the zero degree horizontal angle is directed, north orientation is zero degrees. Displacement of the zero 18
rotation the angular position of the luminaire around the axis through the light center that is an
ANSMESNA RP-22-96
extension of the O-180 degree horizontal angle. When viewed from the 180 degree angle [mast arm end] rotation clockwise is a positive angle. See orientation and tilt.
Safe-Stopping-Sight-Distance (SSSD) estimated values assume that the average prevailing speeds in a straight and level tunnel approach roadway are at, or near, the posted speed limit. For accurate calculation of stopping sight distance, refer to the American Association of State Highway and Transportation Officials (AASHTO), “A -Policy on Geometric Design of Highways and Streets,” 1990. Systeme Internationale, SI a measurement system used throughout the world, commonly referred to as the metric system. Public Law loo-418 designated the metric system as the preferred system of weights and measures for the United States. threshold zone the area inside the tunnel where a transition is made from the high natural lighting level outside the tunnel to the beginning of the transition zones. tilt the angular position of the luminaire around an axis through the light center and along the 90-270 degree horizontal angle. When the luminaire is level the tilt is zero degrees. Displacement of the zero degree horizontal end [street side] of the luminaire upward is a positive angle. See orientation and rotation.
transition
zone(s) areas which allow motorists to achieve appropriate eye adaptation by incrementally reducing the level of luminance required in the threshold zone to the luminance level of the interior zone.
veiling luminance a luminance superimposed on the retinal image which reduces its contrast. It is this veiling effect produced by bright sources or areas in the visual field that results in decreased visual performance and visibility. visibility
the quality or state of being perceivable by the eye: In many outdoor applications,‘visibility is defined in terms of the distance at which an object can just be perceived by the eye. In indoor applications it usually is defined in terms of the contrast or size of a standard test object, observed under standardized view conditions, having the same threshold as the given object.
visibility index, VI a measure closely related to visibility level, used in connection with road lighting applications. visibility level, VL a contrast multiplier to be applied to the visibility reference function to provide the luminance contrast required at different levels of task background luminance to achieve visibility for specified conditions relating to the task and observer. visual acuity a measure
of the ability to distinguish fine details. Quantitatively, it is the reciprocal of the angular separation in minutes of two lines of width subtending one minute of arc when the lines are just resolvable as separate.
visual angle the angle subtended detail at the point of observation. sured in minutes of arc.
by an object or It usually is mea-
19
ANSI/IESNA
RP-22-96
ANNEX A Calculation
Method
(This annex is not a part of the American Standard ANWIESNA RP-22-1996.) A.1
Calculation
A.1 .I
General
National
Procedure
Methods for assessing the quantity of light coming directly from a luminaire to a given point are described in Appendix B of ANSVIESNA RP-8.1 The light level in a tunnel will be higher than what is indicated by direct calculations because of the contribution of light reflected and interreflected from the tunnel’s surfaces. The degree that the reflected light contributes to the luminance of the interior tunnel surfaces varies with the surface’s maintained reflectance, location, and geometry. This appendix describes a process suitable for calculating direct and reflected light contributions to the luminance of tunnel surfaces for straight tunnel sections. Before the design calculations lowing should be determined: l
l
l
are started, the fol-
Luminances required in the threshold zone, transition zone, and tunnel interior. (See Table 3, Figure 2, and Figure 3). Acceptable uniformity ratios. (See Section 6.4.6). Lightsources and lamp sizes to be used. (See
Section 8.1). l
Luminaire types and photometric
characteristics.
The standard methodology for tunnel analysis is based on finite element techniques. In order to develop a methodology for handling luminance calculations in tunnels, several factors and relationships must be investigated: l
The surface of the walls and ceiling must be split into flat finite zones which closely or exactly match the tunnel geometry, a process known as “discretization.” A given zone will have a luminance directly from a given luminaire. This luminance will be dependent upon luminaire candlepower, luminaire/tunnel surface zone geometry, surface zone reflectance, and direction of reflection, This can be referred to as the first reflection luminance.
20
The points on the roadway at which pavement luminance must be calculated will receive light both directly from the luminaires and indirectly from the walls and ceiling, and thus, the computation algorithms will be more accurate if they include the additional indirect contribution. . An important variable will be the tunnel crosssection, which may be rectangular, or a variety of other shapes incorporating sloped or curved surfaces. l The surface area luminance will be increased above the first reflection luminance because of light received from other surface areas that are also receiving light. Thus there is a surface area luminance because of the second and subsequent reflections, that is, the interreflection of light flux between all of the various discrete zones. l
Calculation of the horizontal illuminance or pavement luminance at a point on the roadway requires the following seven steps: 1. Calculate the direct component from the first luminaire using the Inverse Square and Cosine Laws, and the existing methodology.2 2. Repeat for all other luminaires and sum the values to calculate the total direct component from the entire lighting system. the walls and ceiling into zones. 3. Subdivide These zones will reflect light from each luminaire to the pavement observation point. Identify the size and centerpoint location of each zone. 4. Calculate the illuminance in the plane of the first zone at the zone centerpoint by summing the contributions from each luminaire. Repeat for each zone. 5. By applying the zone reflectance function, calculate the intensity reflected by the zone to the pavement observation point. 6. Treat each zone as a luminaire by using the calculated intensities to determine the pavement observation point illuminance and luminance using the existing methodology,’ summing for all zones. 7. Repeat steps 4, 5, and 6 to determine the total indirect component for the first reflection for each pavement observation point required. Details of these steps are outlined in the next section.
A.2.1
Computation of the Direct Component
The illuminance or pavement luminance created by direct light received from a luminaire can be computed in accordance with the existing method-
ANSI/IESNA
ology,2 i.e., in a manner identical to that used for roadway lighting. Point-by-point tabulations thus can be produced. In this procedure, y and $ are the horizontal and vertical photometric angles of I, the luminous intensity. These are measured respectively from nadir, and from a lateral reference line perpendicular to the curb. Figure Al illustrates a level ceiling mounted tunnel luminaire, showing identical coordinate convention to reference 20, Figure Bl. Figure A2a is derived from Figure Al, to be compared to Figure A2b which represents the photometric angles applicable to a vertically-positioned wall mounted luminaire. The reference zero vertical angle is always the nadir direction extending vertically down from the luminaire, but it must be ensured that the luminaire has been photometered in this mounting orientation before the photometric data tables can be used directly.
A.2.2
Discretization
RP-22-96
of the Tunnel Surfaces
Subdividing, or discretizing, the tunnel walls and ceiling into zones allows calculation of the interreflected components by treating each zone as a receiver of light from the luminaires and a reflector of light to the pavement computation points. In the simplest case of a tunnel with a rectangular cross-section, vertical zones can be developed by subdividing each wall horizontally and vertically, and horizontal zones are formed on the ceiling by subdividing laterally and longitudinally. In the case of a tunnel with angled or curved surfaces, the surfaces likewise can be subdivided and approximated by a series of flat zones with differing slope angles.
Figure Al. The reflectance angles for a ceilingmounted luminaire (from reference 2).
(a) Figure A2. The photometric
angles for a ceiling-mounted
luminaire (a) and,a wall-mounted
luminaire (b).
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ANSI/IESNA
RP-22-96
The size of zones, both widths and lengths, must be chosen in developing the inter-reflection sctieme. The use of a very large number of small zones will provide a high degree of accuracy, but may require excessive time in performing the reflected light calculations. Conversely, large zones may provide less accuracy, but can reduce computation time. Ideally, zone sizes will be chosen which are small enough not to compromise computational accuracy, but large enough not to entail computer time unnecessarily. The sizes of the wall and ceiling zones required for accurate computation vary depending on tunnel geometry and the form of the lighting system. The use of luminaires with asymmetric photometrics tends to require smaller zones. It is recommended that calculations be performed on an iterative basis until the improvement in accuracy obtained by going to smaller zones is negligible.
A.2.3
Computation of the Indirect Component of llluminance
Figure A3 illustrates the geometry of a reflecting wall or ceiling surface zone, receiving a light ray of intensity I($,$ from a luminaire L. Figure A4 shows the identical reflecting zone and additional construction lines, indicating that it lies at a slope angle from the vertical, S. The value of S is’general, and therefore can be used to represent zones on the left wall, ceiling, or right wall. (Slope angles for right wall zones are negative.)
To perform the required computation, X, Y, and Z coordinates must be known for the luminaire, reflecting zone centerpoint, and the pavement computation point. From these coordinates, X0, YO, Z,,, X1, Y,, and Z, are determined, defined as follows: X0 = X coordinate of the luminaire minus the X coordinate of the zone centerpoint. YO = Y coordinate of the luminaire minus the Y coordinate of the zone centerpoint. ZO = Z coordinate of the luminaire minus the Z coordinate of the zone centerpoint. X1 = X coordinate of the pavement computation point minus the X coordinate of the zone centerpoint. Y, = Y coordinate of the pavement computation point minus the Y coordinate of the zone centerpoint. Z, = Height of the zone centerpoint above the pavement computation point. Given these dimensional quantities, angles 4 and y are computed:
the values of
@= tan-1 (Y, / X0) y = tan-l (G$
(1)
/ ZO)
(2)
The value of S, the slope angle of the reflecting zone measured from the surface normal to the downward vertical, will be known from tunnel geometry. For the general case of any given luminaire location, and a known location and slope
AC Is h~rizonlfd and parallel to the X axis /
Figure A3. The general geometry for a reflecting
22
surface zone.
Figure A4. The luminaire (L) and surface zone geometry that defines 0.
ANSVIESNA RP-22-96
angle of a defined reflecting zone, the illuminance at the center of the zone and in the plane of the zone, EC,,is given by:
E. = 21C&r)case Do where: Do = distance from the luminaire terpoint E. can be calculated using: Do=dx;+
(3)
to the zone cen-
Y:+z:
(4)
dence and reflection, Lo will represent the zone luminance as viewed by an observer from the particular direction of reflection. E. is assumed to be uniform over the zone, although it is normally calculated for the centerpoint. (More rigorous calculations can be made where Eo is calculated by the same above-described manner at numerous points over the zone surface and the values then may be averaged.) Equation 8a can be used to determine the wall luminance at any point, using equation 3 to calculate E. at that point. Determination of the diffuse component of reflectance is normally sufficient for tunnel lighting computations, and the relationship then becomes:
and:
e = cos-’ X0-Zocot s 1 ( csc S - Do
(5) Lo=
where: 0” < S < 90” Information concerning the derivation of the formula for 8 is provided in reference 21. The above formula is a reduction of the expression provided in equation 9 of this reference. In the case of a horizontal zone, the slope angle S = O”, and the cosecant and cotangents are indeterminate. 8 then reduces to: O= cos-1
(
go
1
forS=O”
(6)
In the case of a vertical zone, the slope angle S = 90” and 0 is then is given by: e = cos-f
The value of 8 should cases.
A.2.4
2% for S = 900 ( Do1 compute
g-E0
where: p = diffuse reflectance n = pi Lo is in cd/m2 E. is in Iux
factor
Use of the diffuse reflectance provides another simplification: The luminance pattern on the tunnel surface will be independent of the location of an observer viewing the zone directly, unlike the case where the BRDF is applied. Later practices, however, may incorporate the use of BRDF. To determine reflected intensity in a specified direction, the intensity perpendicular to the zone surface first is found: I’ = Lo - A0
to be
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