ANWIESNA RP-22-96
American National Standard Practice
for Tunnel Lighting
Prepared
by the IESNA Roadway
Lighting Subcommittee
on Tunnels and Underpasses
Suggestions for revisions to this document
Prepared by the
IESNA Roadway Lighting Subcommittee
on Tunnels and Underpasses
Antanas Ketvirtis, 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, Vice Chair 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* 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 Member **Honorary Member
ANSI/IESNA RF’-22-96
Copyright 1996 by the Illuminating Engineering Society of North America.
Approved by the IESNA Board of Directors, May 13, 1996, as a Transaction of the Illuminating Engineering Society of North America.
A// rights reserved. No part of this publication may be reproduced in any form, in any electronic retrieval system or otherwise, without prior written permission of the IESNA.
Published by the Illuminating Engineering Society of North America, 120 Wall Street, New York, New York 10005.
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 feed- back and comments.
CONTENTS
1.0
Introduction
. . . 1
2.0Physical Characteristics
...
.1
2.1 Definition of a Tunnel ... .l 2.2 Tunnel Classification. ... 1 2.2.1 Short Tunnel.. ... .l 2.2.2 Long Tunnel ... 12.2.3 Divided and Undivided Tunnels ... .l 2.2.4 Underpasses and Overpasses ... 2
3.0
Factors Influencing Tunnel Lighting Needs ... .2
3.1 General ... . ... 2
3.2 Geographic Location ... 2
3.3 Climatic Conditions ... 2
3.4 Tunnel Structure Orientation ... 2
3.5 Traffic Speed ... .3
3.6 Traffic Volume ... .3
3.7 Materials Used in Tunnel Construction ... 3
3.8 Divided and Undivided Structures ... 3
3.9 Tunnels with Special Portal Design ... .3
4.0
Visibility at the Tunnel Approach and Portal ...
44.1 General ... 4
4.2 Pavement Type at Tunnel Approaches ... 4
4.3 Black Hole Effect ... 4
4.4 Black-Out Effect ... 5
4.5 Adaptation Point ... 5
5.0
Luminance of Tunnel Interior Surfaces ... 5
5.1 Architectural Features of Tunnel Cross Section ... .5
5.2 Pavement, Wall, and Ceiling Materials, and Reflective Characteristics ... .5
5.3 Wide and Narrow Tunnels ...
5
6.0
Lighting Design Criteria ...
56.1 General ... 5
6.2 Lighting Requirements.. ... 5
6.3 Assessment of the Major Factors Influencing Lighting Design ... .6
6.4 Method of Determination of Luminance Levels ... .6
6.4.1 Luminance Values in Threshold Zone ... 6
6.4.2 Threshold and Transition Zones ... 6
6.4.3 Tunnel Interior Zone.. ... 6
6.4.4 Nighttime Luminance ... 6
6.4.5 Non-Roadway Surface Luminances ... 8
6.4.6 Uniformity Ratios.. ... 8
6.5 Flicker Effect ... ... 9
ANSI/IESNA RP-22-96
7.0
8.0
Light Application Techniques ...
9
7.1 Symmetrical Light Distribution.. ... 9
7.2 Asymmetrical Light Distribution-Negative Contrast ... 9
7.3 Asymmetrical Light Distribution-Positive Contrast ... .9
Lighting and Electrical Equipment.. ... .9
8.1 Light Sources ... 9
8.1 .I Fluorescent.. ... 10
8.1.2 Low Pressure Sodium (LPS) ... 10
8.1.3 High Pressure Sodium (HPS). ... l-0 8.1.4 Metal Halide (MH) ... 10
8.1.5 Other Light Sources ... .lO 8.2 Luminaires ... 10
8.3 Electric Power Supply and Distribution ... .l 1 8.4 Switching and Control ... 11
Lighting System Economics. ...
119.1 General ... 11
9.2 Initial Cost ... 11
9.3 Life-Cycle Economic Analysis ... .ll
Maintenance Considerations
... .12References
. . . ... .._ ... 14Glossary
...
15Annex A Calculation Method ...
20Annex 6
Method of Computing Luminance Levels in the Threshold Zone ... .26
General ... .I2 Lamp Lumen Depreciation ... 12
Luminaire Dirt Depreciation.. ... 12
Tunnel Surface Reflectance Depreciation ... .12
10.4.1 Selection of Tunnel Surface Reflectance.. ... 12
10.4.2 Reflectance Depreciation ... 12
Luminaire Cleaning and Relamping ... 13
10.5.1 Luminaire Cleaning ... 13
ANSI/IESNA RP-22-96
1 .O INTRODUCTION
This standard practice has the objective of provid- ing information to assist engineers and designers in determining lighting needs, recommending solu- tions, and evaluating resulting visibility at vehicular tunnel approaches and interiors.
This practice is intended also for use by adminis- trators charged with the responsibility of providing a safe visual environment within a tunnel during both daytime and nighttime hours.
The basic design criteria for tunnel lighting are out- lined 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, geomet- ric design, traffic volume, traffic speed, service levels, light source used, and modes of light appli- cation. The lighting designer therefore should con- sider the factors which affect the visibility condi- tions as outlined inSection 3.0.
Treatment of tunnel portals, wall and ceiling sur- faces, and selection of lighting equipment, as well as light sources, maintenance, and lighting eco- nomics are also reviewed and assessed in this document. However, special requirements for pedestrians are not addressed in this document.
2.0 PHYSICAL CHARACTERISTICS
2.1
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).
2.2
Tunnel Classification
In classifying tunnel structures, two factors should be taken into account: structure length and its geometric alignment (visibility through the struc- ture).
2.2.1 Short Tunnel. A straight tunnel having an overall length from portal to portal, along the cen- terline, which is equal to, or less than, the Safe- Stopping-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 align- ment or curvature which prevents motorists from seeing through the structure to the exit end, is con- sidered to be a long tunnel.
2.2.3 Divided and Undivided Tunnels. A struc- ture which consists of two separate enclosures, each designated to accommodate one direction of traffic flow, is considered to be a divided tunnel.
APPROACH
THRESHOLD ZONE
TRANSITION ZONE(S)
INTERIOR ZONE
PORTAL
Figure 1.
The primary external and internal areas associated with and affected by tunnel lighting design.(Formal definitions of each primary area are in the glossary.) .
A structure which consists of a common enclosure to accommodate the traffic flow in both directions is considered an undivided tunnel.
2.2.4 Underpasses and Overpasses. Structures considered to be Underpass or Overpass struc- tures 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.
3.0 FACTORS INFLUENCING TUNNEL
LIGHTING NEEDS
3.1
General
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 fac- tored into the final design criteria, but leaves the decision on their relative weight to the lighting designer.3.2
Geographic Location
With respect to the geographic location, tunnel lighting design may be affected by the following:
l Surrounding land character
l Type of growth surrounding tunnel structure l Solar altitude and azimuth
3.3
Climatic Conditions
Climatic conditions which influence the lighting system design include the following:
l Temperature range l Humidity levels
l Seasonal changes in natural growth l Presence or absence of snow
l 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 east- west 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 por- tal, especially during winter months at higher lati-
TABLE 1: AASHTO STOPPING SIGHT DISTANCE (Wet Pavement)
Traffic Speed (estimated km/h and mph1
Estimated Safe Stopping Sight Distance (SSSD) t
1
Kilometers -per Hour Miles per Hour Meters
I I I 50
30
60
60
40
90
80
50
140
90
55
160
10060
190
11065
220
Feet200
300
450
530
620
720
Refer to American Association of State Highway and Transportation Officials (AASHTO) “A Policy on Geometric Design of Highways and Streets,” 1990 for accurate calculation of stopping sight distance.
tAssumes average prevailing speeds in a straight and level tunnel approach roadway are at, or near, the posted speed limit of the facility. For other geometric conditions, refer to the AASHTO document.
ANSIIIESNA RP-22-96
tudes. If the sun is close to the viewing angle of the portal during an approach to a tunnel with these orientations, the luminance of the sky will be very high, creating a high veiling 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 tun- nel under a river. Highly reflective surfaces outside of a portal, particularly those with specular charac- teristics, can also contribute to elevating the lumi- nance 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 dis- cussed 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 lumi- nance 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 signifi- cantly 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 signifi- cance in determining not only tunnel interior lumi- nance 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.
A high traffic volume also implies a need to main- tain 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 tun- nel. Curved portals may permit greater contribu- tion of daylight towards the threshold zone lighting. In designing a lighting system, materials used in the tunnel structure are of considerable impor- tance, particularly with respect to their characteris- tics of reflectance. For example, tunnel wall sur- faces may be finished with untreated rock, raw concrete, epoxy paint, concrete sealer, or glazed ceramic tiles. The maintained reflectance coeff i- cient 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 regard- ed 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 sun- screens, solar galleries, and other similar devices, whereby the daylight is used in reduced intensity as an intermediate level between the outdoor light- ing 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.
I
SECONDS.
0
2
4
6
8
10 12 14 16Figure
2. Recommended luminance reduction steps for the threshold zone and the transitionzone inside a tunnel.
Caution should be exercised when using sun- screen 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 essen- tial in order to provide adequate visibility at the
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 differ- ence 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 physio- logical 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 per- ceptible 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
Architectural
Features of Tunnel
Cross-Section
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 architectslengi- neers. 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.
The reflectance of the tunnel pavement will have a considerable impact on the amount of light required. The visibility of an object on the pave- ment 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
Wide and Narrow Tunnels
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 interreflec- tion 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 con- trast. If the interior surfaces of tunnels are treated with low reflectance materials, or are poorly main- tained, interreflection may be negligible.
6.0 LIGHTING DESIGN CRITERIA
6.1
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 the- oretical considerations, but also on information drawn from practical experience and engineering judgment.
6.2
Lighting Requirements
Whether daytime lighting is to be provided in tun- nels of different lengths will depend on a number of factors. A summary of these conditions, including recommendations for the threshold zone of the tun- nel, is included in.
Figure 2, Figure 3, Table 2,
andTable 3.
Figure 3.
Various tunnel approach scenes pre- pared 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 lightingrequirements 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 inSection 3.0.
for the tunnel being designed. Changes to the base values derived from the methods given inSection 6.4
may be as large as *20 percent depending on the specific conditions.
6.4
Methods of Determination of
Luminance Levels
This section discusses the methods appropriate for the determination of luminance values within the tunnel. A calculation method for use in predict- ing 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 Determine maintenance factor.
l Determine percent of Lth from
Table 2.
l Determine the tunnel scene closest to that of the
design tunnel
(Figure 3).
l Determine the traffic speed and orientation. l Read the appropriate luminance value from
Table
3 and factor by the percent found inTable 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 deter- mining the equivalent veiling luminance (Lseq). 6.4.2 Threshold and Transition Zones. A sample for the reduction of luminance levels in the thresh- old and in the transition zones is shown inFigure
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 interi- or 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 exteri- or luminance; therefore, a nighttime pavement luminance of 2.5 cd/m2 minimum is recommend- ed for the entire length of the tunnel. (This lumi- nance value has been derived by consensus among experts.‘) The approach and exit road- ways should have a luminance level of no less than one-third the tunnel interior level for a dis- tance 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 WALL REFLECTANCE
’ light Traffic Volume < 75,000 AADT Low Wail Reflectance < 30% Heavy Tmftk Volume > 75,000 AADT High Wall Reflectance > 30%
Table 3
Recommended Daytime Maintained Average Pavement Luminance Levels in the Threshold
Zone of Vehicular Tunnels (Lth)
Approach Characteristics* Scene 1.2.3 Urban T& Scene 4.6.6 Mountain Tunnel Scene 7.8 Traffic Speed km/h mph 100 60 80 50 60 40 100 60 80 60 60 40 I North 250 220 180 320 280 230 Driver Direction I East-West I South cd/m2 310 370 260 320 220 270 280 310 240 270 200 220
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.
TABLE 4
Daytime Interior Zone Average Luminance Recommended from the Road
Interior zone average road surface luminance in cd/m*
Traffic Flow
Traffic
Low
Speed
5 2,400AADT
> 2,400 AADT
Medium
< 24,000 AADT
Heavy
2 24000 AADT
100 km/h (60 mph) 6 8 10 80 km/h (50 mph) 4 6a
60 km/h (40 mph) 3 4 66.4.5 Non-Roadway Surface Luminances. In general, interior surfaces with high luminances will decrease the black hole effect, improve the visibili- ty 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 andSection
5.0. However, higherinterior surface luminance does not always improve visibility.
Some wall luminance, however, is always neces- sary. 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 ben- eficial in tunnels where the threshold slopes down- hill, 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.
Maintenance aspects should also be considered when targeting an improved luminance value for a particular surface. Some surfaces, such as shoul- ders, 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 ade- quate 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 3.5to 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 applica- ble 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 levelsdecreasing smoothly throughout the transition zone(s), and into the interior zone. It is intended that the luminance decrease with smooth transi- tions. 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 unifor- mity requirements for the average light level deter- mined by
Figure 2.
These uniformity ratios are applicable to the road- way pavement and to the portion of the non-road- way surfaces requiring luminance. It is not practi- cal 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 pro- duce undesirable behavioral sensations.
Figure
4 illustrates the range of luminaire cyclesper second that are considered to produce the disturbing effects. It is recommended that the designer avoid luminaire spacing within the annoy- ance 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
Switching Steps in Threshold and
Transition Zones
Tunnel threshold and its interior lighting require- ments vary during daily operation as a result of the changes in external luminances created by weath- er conditions and/or the position of the sun. For the purpose of maintaining luminance ratios between exterior and interior surfaces during varying ambi- ent 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 day- time levels to nighttime levels should be moderate- ly stepped to avoid abrupt changes in illumination.
7.0 LIGHT APPLICATION TECHNIQUES
7.1
Symmetrical Light Distribution
Symmetrical light distributions used in tunnel light- ing design will produce a uniform luminance throughout the tunnel interior, particularly when lin- ear sources are used. However, relatively low con- trast values will be generated.
7.2
Asymmetrical Light Distribution-
Negative Contrast
The ALD-NC system is also known as Counter-
ANSI/IESNA RP-22-96
I2 3 4 5 6 7 6 91011I21
WMINAIRE CYCLES PER SECOND
Figure
4. The stroboscopic effect produced whena motorist passes closely-spaced light sources in a tunnel can result in undesirable behavior and sensations.
beam Lighting (CBL). Light is predominantly dis- tributed toward the driver providing high pavement luminance and low object luminance creating neg- ative contrast.
7.3
Asymmetrical Light Distribution-
Positive Contrast
The ALD-PC system, also known as Pro-beam Lighting (PBL), is similar to that of the Counter- beam light application technique, except the direction of the main beam of light is in the direc- tion 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 selec- tion of light sources for tunnel lighting:
l Efficacy
l Lamp lumen output (lamp size) l Life
l Lamp lumen depreciation l Ambient temperature l Cost (lamp and lu’minaire)
l Restrike time
l Luminaire light distribution
l Physical size (lamp and luminaire)
. Physical durability (lamp and luminaire).
l Color temperature
8.1.3 High Pressure Sodium (HPS). High pres- sure sodium lamps have a wide selection of lamp sizes, increased life ratings, compact size, and are easily optically controlled.
The advantages and disadvantages of the various viable sources are discussed in the following para- graphs.
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.
8.1.1 Fluorescent. Fluorescent lamps are fre- quently 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 fre- quently 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 interrup- tion, (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 depre- ciation over life (at the expense of increased power consumption over the same period).
The disadvantages include: (1) high lamp replace- ment cost, (2) possible large luminaire size, (3) shorter lamp life than HPS lamps, (4) minimal con- trol of light distribution, (5) poor Color Rendering
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 resul- tant discomfort and/or disability glare problems, as well as non-uniform wall brightness and/or stria- tions, 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 shut- down.
8.15 Other Light Sources. It is rare that an alter- nate 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
Index (CRI), and (6) difficulty of maintaining the luminaire dust-tight and water-tight for larger enclosures.
Tunnel lighting luminaires must be ruggedly con- strutted to withstand the harsh environment found in all tunnels. Vibration, air turbulence caused by
ANSIIIESNA RP-22-96
vehicles, exhaust fumes, road dirt, salt (in some climates), and the periodic washing of tunnels with industrial detergents and high pressure spray equipment are some of the conditions to which luminaires are exposed.
The following are factors that must be evaluated in the design, selection, installation, and testing of tunnel lighting equipment:
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 dissimi- lar materials (e.g. concrete).
l Physical strength sufficient to prevent warping,
twisting, or deforming during installation or ser- vicing.
l Highest and lowest ambient operating tempera-
ture within the tunnel.
l Luminaires which permit specific directional light
control, resulting in improved contrast and over- all visibility conditions.
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 provid- ed to vary the light output of the lighting system. Step switching can be controlled by a set of elec- tronic photocontrols that monitor outdoor light at the tunnel entrance.
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.
9.0 LIGHTING SYSTEM ECONOMICS
9.1
General
Lighting system economic analysis consists of the following major aspects:
l Selected lighting level l Type of light source
l Quality of lighting equipment l Method of equipment installation l Maintenance and operation procedures l 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 equip- ment (lamps, luminaires), initial capital investment does not provide complete information on the rela- tive 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 effi- cacy. Also, the initial costs do not reflect the main- tenance 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 dif- ferent lighting systems, an economic analysis based on life-cycle should be used. Such analysis takes into consideration not only the capital invest- ment, but also such factors as:
l Lamp replacement l Energy cost
l Maintenance and operation expenses l Equipment replacement caused by
traffic accidents
l 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 accura- cy of the input data.
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 mainte- nance. 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 con- sider its capability to withstand washing by apply- ing high pressure spray and mechanical brushes. Repair of the luminaire components must be accomplished with minimal time spent in the tun- nel. 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 specif- ic importance. Aluminum and carbon steel compo- nents exposed to moisture and chemicals may allow galvanic reactions that cause early deteriora- tion 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 lumi- naire 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.’
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 glass- ware/lenses and reflectors. Decisions about LDD factor value (and its relation to the number of fix- tures required to meet maintained service levels) and the commitment of resources to regular main- tenance 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 sig- nificant impact upon ‘effectiveness of light fixtures in meeting the lighting design criteria.
For new tunnels, the lighting designer should partic- ipate 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 physi- cal 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 oper- ating cost of lighting required in the threshold zone. For existing tunnels requiring retrofit or recon- structed 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 subter- ranean 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
cost of higher quality fixtures should be included inPrevention of accidents in tunnels and the poten- tial secondary effect of explosion, fire, or noxious fumes is particularly dependent on maintenance of good lighting and visibility.
the life-cycle economic analysis discussed in
Section
9.0. Cleaning schedules should be coor-dinated with relamping schedules as much as possible to minimize lane closures.
Maintenance of lighting fixtures in tunnels usually requires lane closures which a well developed cleaning and relamping schedule should minimize.
10.5.2 Relamping. Consideration of group relamp- ing is more critical in tunnel lighting maintenance programs than for most other lighting systems because of traffic restrictions required in tunnels. 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 sur- faces is required. The internal cleaning require- ments will vary depending on fixture specifica- tions. Proposed cleaning schedules and the initial
Easy, quick relamping (as well as internal clean- ing) is affected by the construction, latching, and accessibility of fixtures. These factors should be thoroughly considered in design. Poor designs rel- ative to location, accessibility to the fixture, or abili- ty of workmen (with gloves) to open, service, and close fixtures will significantly affect operating costs which should be considered in
Section 9.0.
References
(These references are not part of the American National Standard ANSI/IESNA RP-22-1996).
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
American National Standard Practice for Roadway Lighting, RP-8-83. New York: Illum- inating Engineering Society of North America, 1983 (Reaffirmed 1993).
14. Walthert, R. “Tunnel Lighting Systems.” Inter- national Lighting Review, Vol. 4, p. 112, 1977b.
“An Informational Guide for Roadway Lighting” Code G-5, American Association of State Highway and Transportation Officials (AASH- TO), 444 N. Capital Street, N.W., Suite 225, Washington, DC 20001, 1984.
15. Gallati, E., Muller, E. and Riemenschneider, W. “Lighting Values in the Access-Entrance-Zone of a Tunnel.” CIE 20th Session, 1983.*
16. Narisada, K. “Latest Research in Tunnel Light- ing in Japan.” Highway Research Circular No. 137, TRB, 1972.
“Guide for the Lighting of Road Tunnels and Underpasses.” International Commission on Illumination, Publication CIE No. 88, 1990.*
17. Rinalducci, E. “Transitional Adaptation in Tunnel Lighting.” TRB, 1972.
“Tunnel Entrance Lighting: A Survey of Funda- mentals for Determining the Luminance in the Threshold Zone.” CIE Publication No. 61, 1984.*
18. Zwahlen, H.T. “Driver’s Eye Scanning Be- haviour of Tunnel Approaches.” Conf. on Eye Movement and Psychological Process, U.S. Army HEL, Monterey, CA, 1977.
“Guide de I’Eclairage des Tunnels.” Ministere de I’Urbanisme, du Logement et des Trans- ports. (CETU-LYON-FRANCE-MAI), 1985.
19. Adrian and Fleming. “Psychological Basics to the Lighting Levels in the Transition Zone of Tunnels.” LRI Research Project 88 SPL REF3, Feb.’ 1990.
“Code of Practice for the Lighting of Tunnels.” British Standard Institution, BS5489 Part 7. “Offentliche Beleuchtung Strassen tunnels, Galeries und Unterfiirungen.” Leitsatze der Schweizerische Lichttechuischen Gesellschaft (SLG), SN 418915, 1983.
20. Lewin, I. and Heinisch, R. V. “Luminance Calculations for Tunnel Lighting Systems.” Journal of the IESNA, Winter 1988, pp. 74-79.
Adrian, W.K. “Adaptation Luminance when Approaching a Tunnel in Daytime.” Lighting Research and Technology, No. 3-1987.
21. Lewin, I. and Heinisch, R. V. “Further Developments in Tunnel Lighting Compu- tations.” Journal of the IESNA, Winter 1991, pp. 100-107.
Blaser, P. “Counterbeam Lighting, A Proven Alternative for the Lighting of the Entrance Zone of Road Tunnels.” TRB National Confer- ence, Washington, DC, 1990.
22. Committee on Recommendations for .Quality and Quantity of Illumination of the IESNA. 1973. RQQ Report no. 5. “The Predetermin- ation of Contrast Rendition Factors for the Calculation of Equivalent Sphere Illumination.” Journal of the IESNA, Vol. 2, No. 2, p. 149, January 1973.
Schreuder, D.A. Dr. “Practical Determination of Tunnel Entrance Lighting Needs.” TRB Nation- al Conference, Washington, DC, 1991.
23. Adrian, W. Lighting Res. Technol., 14, 1982, pp. 151-159.
Novellas, F. and Peviser, J. “New Lighting Method for Road Tunnels.” CIE Journal 4, No. 2, 1985.*
24. Nakamichi, F., Narisada, K., and Yoshikawa K. Journal Illuminating Engineering Institute of Japan, Vol. 54, No. 10, 1967, pp. 566-581.
Ketvirtis A., P. Eng. FIES. “Visibility Study for Long Vehicular Tunnels.” Journal of the IESNA,
*CIE Publications may be ordered from the United States National Committee of CIE, c/o T. Lemons, TLA Lighting
Jan. 1975. Consultants, Inc., 7 Pond Street, Salem, MA 01970-4819.
13. Ketvirtis A., P. Eng. FIES. “Counterbeam Lighting offers Cost-effective Tunnel Illum- ination.” Toronto: Electrical Systems Engineer, Spring 1990.
Glossary
(This glossary is not part of the American National Standard ANSVIESNA RP-22-1996.)
accommodation
the process by which the eyechanges focus from one distance to another.
adaptation
the process by which the visual sys-tem becomes accustomed to more or less light or light of a different color than it was exposed to dur- ing an immediately preceding period. It results in a change in the sensitivity of the eye to light.
approach
the external roadway area leading to thetunnel.
ballast
a device used with an electric dischargelamp 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 aray reflected in a given direction to the differential luminous flux density incident from a given direc- tion of incidence, which produces it.
brightness
see luminance and subjective bright-ness.
candela, cd
the SI unit of luminous intensity. Onecandela is one lumen per steradian. Formerly can- dle. (See Figure below.)
candela per square meter, cd/m*
theSI
unit ofluminance equal to the uniform luminance of a per- fectly 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.
ANSI/IESNA RP-22-96
candlepower, cp
luminous intensity expressed incandelas. It is no indication of the total light output.
candlepower distribution
curve
a curve, general-ly 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 thecentral or fovea1 part of the visual field, approxi- mately two degrees in diameter. It permits seeing much finer detail than does peripheral vision.
Color Rendering
Index, CRI
measure of thedegree of color shift objects undergo when illumi- nated 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 pres-ence of luminance differences. Quantitatively, it is equal to the reciprocal of the contrast threshold.
contrast see luminance contrast.
contrast threshold
the minimal perceptible con-trast 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 asurface or medium by diffuse reflection to the inci- dent flux.
diffuser
a devise to redirect or scatter the lightfrom a source, primarily by the process of diffuse transmission.
directional
reflectance
coefficient
the reflect-ance in a particular direction for incident ray leav- ing a direction of incidence defined by angles p and y. Also called bidirectional reflectance-distrib- ution function.
disability
glare
glare resulting in reduced visualperformance and visibility. It often is accompanied by discomfort.
See veiling luminance.
discomfort
glare
glare producing discomfort. Itdoes not necessarily interfere with visual perfor- mance or visibility.
equivalent luminous intensity
[of an extended
source at a specified distance]
the intensity of apoint source which would produce the same illumi- nance at that distance. Formerly, apparent lumi- nous intensity of an extended source.
footcandle, fc
the unit of illuminance when the footis 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 [photometricbrightness] 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 lumi- nance of any surface emitting or reflecting light at that rate. Use of this unit is deprecated.
glare
the sensation produced by luminance withinthe visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance , discomfort, or loss in visual perfor- mance and visibility.
See disability glare, discom-
fort glare.
illuminance,
E = d@/dA
the density of the lumi-nous 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 instru-ment 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 fil- ter, driving a digital or analog readout through appropriate circuitry.
illumination
the act of illuminating or state ofbeing illuminated. This term has been used for density of luminous flux on a surface [illuminance] and such use is to be deprecated.
intensity
a shortening of the terms luminous inten-sity and radiant intensity. Often misused for the level of illumination or illuminance.
interior
zone
area within the tunnel after eyeadaptation has been completed.
isocandela line
a line plotted on any appropriatecoordinates to show directions in space, about a source of light in which the candlepower is the same. For a complete exploration the line always in a closed curve. A series of such lines for various illuminance values is called an isolux diagram.
isolux line
one plotted on any appropriate coordi-nates to show all the points on a surface where the illuminance is the same. For a complete explo- ration 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 appropri-ate 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.
lamp
a generic term for an artificial source of light.lamp lumen depreciation factor, LLD
the multipli-er to be used in calculations to relate the initial rated output of light sources to the anticipated minimum rated output based on relamping pro- gram to be used.
light center [of a lamp]
the center of the smallestsphere that would completely contain the light emitting element of the lamp.
light center length [of a lamp]
the distance fromthe light center to a specified reference point on the lamp.
light loss factor, LLF
a factor used in calculatingilluminance 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 mainte- nance factor.
lumen, Im
SI unit of luminous flux. Radiometrically,it is determined’from the radiant power. Photo- metrically, 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 alamp or lamps together with parts designed dis- tribute the light, to position and protect the lamps and to connect the lamps to the power supply.
luminaire dirt depreciation factor, LDD
the multi-plier to be used in the illuminance or luminance calculations to relate the initial illuminance or lumi- nance 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]
thequotient of the luminous flux at an element of the surface surrounding the point, and propagated in directions defined by an elementary cone contain- ing 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.”
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 direc- tion is interpreted as the quotient of luminous intensity in the given direction produced by an ele- ment 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 emit- ting surface due to the attenuation of the transmit- ting media.]
Note:
in common usage the term “brightness” usu-ally 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 bright- ness, used alone, refers to both luminance and sensation. The context usually indicates which meaning is intended. Previous usage notwith- standing, neither the term “brightness“ nor the term “photometric brightness” should be used to denote the concept of luminance.
luminance contrast
the relationship between theluminances of an object and its immediate back- ground. It is equal to [L1-Lz]/L,, [LrL,]/L,, or AL/L, where L, and L2 are the luminances of the back- ground and object, respectively. The form of the equation must be specified. The ratio AL/L, is known as Weber’s fraction.
Note: see
last paragraph of the note under lumi-nance. Because of the relationship among lumi- nance, 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 con- sideration.
