Lighting Research and Technology 2012 Rea 1477153512441163

8/13/2019 Lighting Research and Technology 2012 Rea 1477153512441163

1/15


2/15

The Trotter Paterson Lecture 2012:Whatever happened to visual performance?MS Rea PhD, FSLL

Lighting Research Center, Rensselaer Polytechnic Institute, Troy, NY, USA

Visual performance has been studied since the 1930s to help establish a foundationfor recommended illuminances. Two approaches were taken to research visualperformance, one by Weston in Great Britain and the other by Luckiesh in theUnited States, leading to different recommended illuminances in the twocountries. Because of the energy crisis of the 1970s, applied research into visualperformance was undertaken to resolve the discrepancy, resulting in a model of relative visual performance. More recently, a controversy has emerged regardingthe value of illuminating roadways. Recent research shows that the incremental

improvements in visual performance provided by roadway lighting are correlatedwith the incremental reductions in night-time crashes, demonstrating that anunderstanding of visual performance remains important for lighting practice.

1. A little history

When I began my career in lighting research inthe 1970s, the energy crisis was the main topicof conversation at every level of society.In those circles where electric energy use inbuildings was of central concern, recom-mended light levels became the main topic of debate. In the United States, a sharp ideo-logical line was drawn between the lightingindustry and the evolving set of governmentregulators. The lighting industry had been on a50-year quest for higher and higher light levelsthat, until 1973, had gone unchallenged.Figure 1, from 1959, shows the past, thencurrent, and the forecasted increases in rec-ommended light levels until the 21st century. 1

As energy became a central political topic,government became actively involved withelectric energy use in buildings. The FederalEnergy Agency, later the Department of Energy, was created in the United States

and began to take a much more aggressiverole in questioning the industrys recom-mended light levels, with the implicit goal of reducing them to save electric energy inbuildings. The lighting industry naturallytook issue with this aggressive incursion intotheir domain. They believed they knew whatwas best for the public and, moreover, thatmany of these new governmental regulatorswere not only naive and misguided butperhaps rude as well. 2

As the contentious discussions escalated,those on both sides of the ideological divideagreed that there should be a scientific basisfor recommended light levels. 35 Initially, theindustry thought that by getting governmentregulators to agree to this foundation, theyhad effectively won the battle. The industrybelieved that the icon of the lighting industry,H Richard Blackwell, would dazzle everyoneby laying out the scientific basis for recom-mended light levels, and governmentencroachment into the industrys domainwould simply go away. Blackwell had beenworking o n the relationship between visibilityand recommended illuminance levels for a

Address for correspondence: Mark S Rea, Lighting ResearchCenter, 21 Union Street, Troy, NY 12180, USAE-mail: [email protected]

Lighting Res. Technol. 2012; 0 : 114

The Chartered Institution of Building Services Engineers 2012 10.1177/1477153512441163

at NATIONAL INST. OF TECHNOLOGY - ROURKELA on December 2, 2013lrt.sagepub.comDownloaded from
http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/


3/15

quarter century and had, in fact, developed avisibility model, published as CommissionInternationale de lE clairage (CIE) ReportNo. 19, that had just received internationalapproval. 6 The report that described themodel, they believed, came at a perfect time.It would now simply be a matter of conduct-ing a few small empirical studies to validateBlackwells model (including those studies ledby Dr Stanley W Smith at the Ohio StateUniversity, who supported me throughoutgraduate school) and, by extension, theindustrys recommended light levels. In fact,both industry and government participants inthe debate believed that with just a little moredata, it would be possible to answer unam-biguously how much light was needed inclassrooms, offices, factories and homes,thereby optimizing our electric energy use inbuildings. 7,8 Given the heightened attention

on energy, lighting research laboratoriesaround the world began to study the rolethat illumination levels had on visual per-formance, 920 defined then and now as thespeed and accuracy of processing visualinformation. Indeed, this emphasis on appliedlighting research is the very reason I got intolighting with Dr Smith and why I worked formany years at the National Research CouncilCanada developing the model of relativevisual performance (RVP). 18,2123

Studies of visual performance preceded theenergy crisis of the 1970s by several decades,however. Much of the seminal work on visualperformance was started in the 1930s, both inGreat Britain and in the United States. Theapproach taken in the United States byMatthew Luckiesh in the 1930s set the stagefor the controversy over the recommendedlight levels in the United States 40 years later.

N e w

I E S r e c o m m e n

d e

d f c l e v e

l s

Operating rooms (table)Show windows-daytime

Cloth inspectionWelding

Interior display lightingSewing in clothing industryMajor league baseball

Self service storesService stores

Industrial fineMediumRough

Office Drafting Difficult

GeneralStorage fine

Medium Rough

1 1898

2

5

10

20

50

100

200

500

1000

2000

5000

10,000

1998

1978

Today, recommendedlevels for typical

non-critical areasare about 100 fc

In actionareashundredsof fcwill be usedfor generallighting

Tens of fcwere usedin the past

History ofillumination standards

Typical values

1958

1943

1938

1918

Figure 1 From 1959, the increases in Illuminating Engineer ing Societ y of North America (IESNA) recommendedlevels of illumination in footcandles from the turn of the 20th century together with projected increases in therecommendations until the 21st century 1

2 MS Rea




4/15

Figure 2 is an image of Matthew Luckiesh atthe height of his influence. 24 (Coincidentally,Luckiesh was an adjunct instructor in illumi-nating engineering at Rensselaer PolytechnicInstitute, home of the Lighting ResearchCenter.) By 1940, he had published at least20 books on lighting and visibility and wasthe primary thought leader on the topic of lighting and visual performance in the UnitedStates at that time, although not withoutsome controversy. 25

Luckiesh argued that recommended lightlevels should be prescribed in terms of avisibility threshold. With his collaboratorFrank Moss, he developed a visibility meterthat reduced transmission of light to the eyeto measure threshold visibility for realisticobjects, such as printed type. When the visualtask being seen through the visibility meter

was at the breakpoint between seeing and notseeing, that is at threshold, the visibility levelof that task could be determined relative to astandard target (8-point Bondi Book typeviewed at 14 inches [35.5 cm] and presumablyprinted on white [ 0.7] paper) at a referenceilluminance level (10 footcandles [108 lx]).Through a set of empirical relationshipsbetween target contrast, target size, back-ground luminance and estimated fixationtime, the measured threshold visibility andthe visibility threshold of the standard targetat the reference illuminance level, Luckieshargued that it was possible to scientificallyprescribe an illuminance level for the vis-ual task seen through the visibility meter.Figure 3 is a drawing of his visibility meterfrom his 1937 book with Moss. 26

This intellectual framework developed byLuckiesh was later embraced by Blackwell inthe 1950s, 1960s and 1970s, using his own setof empirical functions and his own version of a visibility meter. 2729 It is surprising, anddisappointing, that Luckiesh never receivedmuch credit for establishing the frameworkfor linking studies of visual threshold torecommended light levels. It is perhaps true,however, that the link could not have beenforged for formal recommendations withoutthe force of Blackwells personality and thatof Blackwells primary advocate, CL CashCrouch, the Technical Director of theIlluminating Engineering Society of NorthAmerica (IESNA). If one reads the lightingliterature from the late 1950s through the1970s, it would be difficult to disagree thatthese two individuals (Figure 4) were the mostimportant advocates for developing a scien-tific basis for recommended light levels in theUnited States. Indeed, they were key combat-ants on the battlefield of debate over energyand light levels throughout the 1970s. 8,3136

In Great Britain during the 1930s, HCWeston took a very different approach thanthat employed by Luckiesh, and subsequentlyby Blackwell. Weston measured the speed and

Figure 2 American lighting and visibility pioneerMatthew Luckiesh 24 in 1940

The Trotter Paterson lecture 2012 3


http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/


5/15

accuracy with which human subjects couldprocess a set of visual targets printed indifferent sizes and contrasts and seen underdifferent illuminance levels. 37,38 From thosedata, Weston developed a set of curves thatdemonstrated the insensitivity of visual per-formance to light level when objects were of large size and high contrast. In fact, Westonshowed that visual performance for visualtargets of the size and contrast of mostprinted reading tasks changed by only a fewpercentages with changes in illuminance levelover several orders of magnitude. Westonsstudies set the stage for what ultimatelytranslated into the recommended levels in

Great Britain (e.g. 300 lx for general illumin-ation), 39 which in the 1960s were very muchlower than those recommended in the UnitedStates (e.g. 1000 lx for general illumination). 1

Because of the marked differences betweenthe recommended light levels in the UnitedStates and in Great Britain, Westons studiesbecame a target for Blackwell and Crouch.Ironically, Crouch used Westons data todevise a nomogram for scientifically basedlight-level recommendations in the mid-1940s, 40 but he later became a convert to thethreshold approach espoused by Blackwell.Blackwell was one of the strongest critics of Westons approach. 41 Figure 5 is from theCIE meeting in Brussels in 1958, showingWeston and Blackwell disagreeing on visualperformance before that congress. 42

In retrospect, Weston, Luckiesh and laterBlackwell were much like the characters in thefable of the Blind Men and the Elephant. 43

Each was carefully examining one aspect of the visual performance elephant; Luckieshand Blackwell focused on determining thethreshold for visibility which is very sensitiveto small changes in light level. Then, byextrapolation to suprathreshold levels, rec-ommendations for relatively high light levelsin offices, schools and other commercialspaces could be justified. 44,45 Weston, on theother hand, focused on measuring the speedand accuracy of processing visual targets wellabove threshold, which are very insensitive tosmall changes in light level, particularly forunrestricted viewing distances. Like the blindmen of the fable, the two approaches arecorrect, but incomplete. Some tasks are of such high contrast and large size that they canbe seen quite well under dim lighting; emer-gency lighting levels in offices are justifiablylow for this reason. 46,47 Other visual tasksrequire very high levels of illuminationbecause they are very small or of low contrast;successfully threading a needle or removing asmall wood splinter from the skin requires ahigh level of illumination.

Figure 3 The LuckieshMoss visibility meter. 26 The userplaces the device (top illustration) on the bridge of thenose and looks through the two eye pieces. Whileviewing a test target (e.g. a manufacturing flaw), theuser turns a knob on the top of the device (not shown)which is geared to a pair of circular, graded neutraldensity filters (bottom illustration), each located behindone eye piece. The user adjusts the transmission throughthe two filters until the test target appears to be justvisible (or invisible), that is, at threshold. At threshold,the scale on the left is a measure of the visibility level of the test target relative to a standard target illuminated to

10 footcandles while viewed at a prescribed distance.The scale on the right is a measure of the illuminance (infootcandles) needed on the test target that would bring itto the same visibility as a standard target illuminated to10 footcandles while viewed at a prescribed distance

4 MS Rea




6/15

Around the time of the energy crisis of the 1970 s and shortly thereafter, a flurry of investigations of visual performance and lightlevels were made in Great Britain 911,14,16,20

and the United States. 12,13,15,1719,48

Reviewing all of these efforts 49 and conductingfurther experiments 21 at photopic and mesopiclight levels to assess visual performance atnear-threshold as well as suprathreshold con-ditions, Mike Ouellette and I developed theRVP model to provide a more complete andaccurate perspective on the disparateapproaches 22,23 and, as it turned out, a basisfor lowering recommended lighting levels inoffices, schools and other commercial spacesin the United States. Today, in fact, theilluminance recommendations in GreatBritain and in the United States are quitesimilar to one another (both are, for example,300 lx for general illumination) and,

Figure 4 H Richard Blackwell and CL (Cash) Crouch at the Illuminating Engineering Society (IES) Southern CaliforniaSection Study Club 30 in 1959

Figure 5 HC Weston (left) and H Richard Blackwell (right)debating light-level recommendations at theCommission Internationale de lEclairage (CIE) 42

Congress in Brussels, 1959





7/15

interestingly, are much the same as thoseproposed in Great Britain in the 1960s. Froma current comparison of these past and presentrecommended light levels, it would seem thatWeston had been largely correct, although atthe time, as Blackwell stated, Great Britainwas the odd man out. 50

2. Where are we now?

National pride aside, it is abundantly clearthat lighting communities around the worldhave simply moved on from an obsession withthe relationship between visual performanceand recommended light levels. In small part,

this is because RVP provides a more completeunderstanding of the relationship betweenillumination levels and visual performance.More importantly, however, technology haslargely moved us from our obsession.Although reading paper-based tasks is stillquite common, many of the critical visualtasks we see are displayed on self-luminousscreens. Screen treatments minimize reflectedglare and easy-to-use software makes it trivialto change font type and size for comfortable

reading. For much of what we read today,unlike what we read in the 1970s, recom-mended illumination levels for visual per-formance are functionally much lessimportant. In addition, the significantlybetter and more energy-efficient lightingtechnologies developed for illuminating build-ing interiors in the last 30 years have made usless concerned with recommended light levels.The efficacy of commercial lighting systemshas increased by at least a factor of two since

the 1960s.51

Higher lighting system efficacy,changes in visual task displays and the lowerrecommended illuminance levels for interiorapplications have combined to reduce theemphasis on developing a scientific basis forrecommending illuminance levels. In sharpcontrast to publications in the 1970s and1980s, it would be very difficult to find arecent technical paper on visual performance

within the context of illuminating the interiorof buildings.

It is interesting to note that Kit Cuttlerecently argued that visual performance issimply no longer important for architecturalapplications. 52 Rather, according to Kit, weshould focus our attention on the luminousexitance of surfaces within the architecturalspace because, he believes, luminous exitanceis related to the most important designcriterion, the perceived brightness of aspace. Although I agree with the largerpoint that Kit has made, namely, that weshould not be obsessed with horizontal illu-minance levels to deliver visual performancein offices and schools, I do take issue with hiscontention that visual performance is nolonger an important topic for lighting.Visual performance should still be an import-ant design criterion in commercial settings forsuch tasks as sewing and lawyering, whereseeing small details and reading fine print arenecessities. Notwithstanding the importanceof visual performance for these niche appli-cations, I agree with Kit that visual perform-ance should not be the basis forrecommending light levels in most commer-cial applications. Other criteria like apparentbrightness 5355 and circadian regulation 56

should begin to attract more formal consid-eration. Rather than completely abandonwhat we have learned about visual perform-ance over the past 80 years, however, I believevisual performance should again be a centraltopic of discussion within the lighting com-munity but we should now centre our atten-tion on outdoor lighting because, through itseffects on visual performance, it seems to

directly affect traffic safety.

3. The model of RVP

The model of RVP is graphically representedfor one target size in Figure 6. In this figure,the relative speed of processing visual infor-mation by the fovea is plotted as a function of

6 MS Rea




8/15

target contrast and target background lumi-nance (i.e. light level). This relationship isshown for just one target size in Figure 6, 15microsteradians ( msr). There are two import-ant regions of visual performance illustratedin this figure, the plateau and the escarp-ment. 58 On the white plateau, large changesin background luminance, target contrast andtarget size have little effect on the speed andaccuracy of processing visual information.This is what Weston had shown in the 1930sand 1940s. On the dark grey escarpment,however, small changes in any of theseparameters can make the difference betweenseeing and not seeing the object. This is whatLuckiesh had shown in the 1930s and 1940s,and what Blackwell stressed in the 1950s and1960s.

The RVP model was originally developedfrom experiments measuring the speed andaccuracy of comparing lists of five-digitnumbers under different light levels andlighting geometries. 18,21 Subsequent studiesusing reaction times to targets of different

sizes and contrasts viewed at different back-ground luminance levels were conducted tovalidate and extend the RVP model. 22,59

More recent studies of visual performancehave also been conducted in various applica-tions, 6064 reinforcing the validity of the RVPmodel, which now seems to be a complete anddetailed representation of the visual perform-ance elephant that obsessed the lightingcommunity in the 1970s and 1980s.

As already noted, most visual tasks that weilluminate in commercial spaces have suffi-ciently high contrast and are of sufficientlylarge size that visual performance is almostalways on the RVP plateau. 65 Thus, changingillumination levels for these applications haslittle, if any, effect on visual performance.Figure 7 is a plan view of the RVP surfacefor targets subtending a solid angle of 4.8 msrat the eyes, a size comparable to 10-pointprinted type seen at 50 cm. The contour plotshows constant levels of visual performanceas a function of light level and contrast. Theun-shaded portion of Figure 7 shows therange of light levels and contrasts typical incommercial offices (the shaded portions areunlikely to be found in these spaces). Visual

R V P

1.00.9

0.9

0.8

0.8

0.7

0.7

0.6

0.6

0.5

0.5

0.4

0.4

0.3

0.3

0.2

0.2

0.1

0.1

0

0

1.0

C o n t r a s t

0.01

0.1

1.0

10.0

L u m i

n a n c e

( c d / m

2 )

Figure 6 Relationship among background luminance,target contrast and relative visual performance (RVP) fora target having a solid angular size of 15 microsteradians(msr). This size corresponds to that of the standardsmall target (20cm 20cm) used by the IlluminatingEngineering Society of North America in the specificationof visibility levels for roadway lighting viewed from46 m 57

1

0.8

0.6

0.4 C o n

t r a s t

0.2

010 100

RVP 0.9

RVP 0.0

> 0.7 RVP < 0.9

> 0.0 RVP 0.7

Luminance (cd/m 2)

Figure 7 Contours of constant relative visual perform-ance (RVP) values as a function of light level andcontrast. The unshaded area in the upper-right portionof the figure corresponds to the light-level range ( 4 50 cd/ m 2 , which corresponds to white paper under illumin-ances of at least 200 lx) and luminance contrast range(4 0.7, based on field measurements by Dillon et al.) 65 of typical office lighting applications. The size of the visualst imulus, 4.8 sr, corresponds to the typical size of 10-point type viewed from 50cm. An age of 20 years isassumed for the purpose of RVP calculations





9/15

performance is insensitive to either factor(RVP 4 0.9) under these conditions, so differ-ences in illuminance levels for most printedtext have little effect on the speed andaccuracy of reading.

In actual applications, it is also importantto note that people will usually compensatefor losses in visibility due to low light levelsoutside the range illustrated in Figure 7 bychanging their behaviour. Young people withnormal vision will bring the task closer to theeyes to increase visual target size 66 and thoseof us over 45 years of age (presbyopes) donour corrective lenses to bring the task intofocus. Furthermore, people will often bringadditional illumination to the task if it is hardto see, by either utilizing daylight or adjust-able task lights. 67 All of these behaviours areimplicitly performed to keep the visual taskaway from the escarpment, and on the plat-eau of visual performance. Clearly, an obses-sion with visual performance in commercialspaces is misplaced and, as Kit suggests, weshould change our focus for theseapplications.

4. Roadway lightingCompensatory behavioural strategies to stayon the visual performance plateau are oftennot available to us when we drive (e.g. usinghigh-beam headlights all the time we drive).When we experience a loss of visibility on theroad, we slow down (or, at least, we shouldslow down!) to provide us with enough timeto respond to objects that might be hazards. 68

Thus, understanding the relationship between

roadway lighting and visual performance isstill quite important. Figure 8 illustrates theinfluence of light level and contrast on visualperformance under conditions typical forroadway applications. The un-shaded por-tions of this paired figure (Figure 8(a) and(b)) show the range of light levels andcontrasts common for roadways at night.Many times, in fact, objects on or near the

roadway are on the escarpment of the visualperformance surface or worse (i.e. hazards arebelow threshold). Unlike interior commercialapplications, visual performance is quitesensitive to lighting and contrast parametersfor outdoor, night-time applications likeroadways, particularly for older drivers(Figure 8(b)). Thus, while it is largely truethat no one dies from bad lighting in theoffice, bad lighting on the roadway can easilybe lethal. 70 Luckiesh and Blackwell werelargely correct then for these applicationswhere visual performance really matters.

Recently, the Lighting Research Center hasbeen utilizing the RVP model to design andevaluate lighting systems for roadway

RVP 0.9

RVP 0.0

> 0.7 RVP < 0.9

> 0.0 RVP 0.7

RVP 0.9

RVP 0.0

> 0.7 RVP < 0.9

> 0.0 RVP 0.7

1

0.8

0.6

0.4 C o n

t r a s

t

0.2

00.1 1

Luminance (cd/m 2)

1

0.8

0.6

0.4 C o n

t r a s

t

0.2

00.1 1

Luminance (cd/m 2)

Figure 8 Contours of constant relative visual perform-ance (RVP) values as a function of light level and contrastfor young (8a, top) and older (8b, bottom) drivers. Theunshaded area in the lower portions of both figurescorrespond to the light-level range (0.1cd/m 2 1cd/m 2 ,which corresponds to asphalt under illuminances of 3 lx30lx) and luminance contrast range ( 5 0.7 based onanalyses by Bullough et al. 69 ) typical of night-timedriving conditions. The size of the visual stimulus,15 sr, corresponds to that of the standard small target(20 cm 20 c m) used by the Illuminating EngineeringSociety of North America in the specification of visibilitylevels for roadway lighting, viewed from 46m away 57

8 MS Rea


http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/http://lrt.sagepub.com/


10/15

applications. Crosswalk lighting is one suchapplication (Figure 9). 64,69 Fortunately, ped-estrian deaths from vehicles are few, but theyare almost always associated with poor visi-bility. After striking a pedestrian with anautomobile, drivers often say, I never saw theperson. Encouraging pedestrians to usecrosswalks is important, but people are stilloften struck by cars in or near the cross-walk. 71 In fact, using the RVP model to assessthe visibility provided by many crosswalklighting systems, we have found that the mostcommon type of crosswalk lighting systemused in North America provides rather poorvisibility of pedestrians, 69 even though itprovides relatively high levels of illumination.The contrast of the pedestrian against theroadway background is often low for anoncoming driver of a car with headlampsbecause of the combined spatial distributionsof illumination provided by the headlampsand by the fixed luminaire near the crosswalk.The RVP model provides important insightinto the interactions between target size,target contrast and background luminanceas they are affected by headlights and fixed,roadway illumination systems.

More generally, we have been using theRVP model to determine whether fixed

roadway lighting systems contribute tosafe driving. 72 Communities in both GreatBritain and the United States are sharplydivided as to the perceived benefits of road-way lighting; some say they are a waste of energy and money, and some say they areessential for safety. Lighting experts haveclaimed a benefit of 30% reduction in night-time traffic (car-to-car) collisions, 73 whileothers claim there is no evidence for anysafety benefits. 74 Together with my col-leagues, John Bullough at the LightingResearch Center and Eric Donnell atPennsylvania State University, we have beenable to examine the statistical relationshipbetween the presence of street lights (andheadlights) and night-time vehicle collisionsin the state of Minnesota, 75,76 together withthe visual performance benefits provided byroadway intersection lighting systems inMinnesota. Minnesota is an unusual statebecause it not only keeps intersection-specific collision data, but it also has aformal, documented procedure for illuminat-ing those intersections. What we were able todo, we believe for the very first time, is linkthe visual performance benefits delivered bythe lighting systems in Minnesota to thestatistical crash data in Minnesota.

The RVP model 23 was an essential link inthat chain of logic. We were able to create avirtual, photometrically accurate intersectionwith and without roadway lighting (automo-bile headlights were always on) to assess thespeed and accuracy with which a virtualdriver could determine with the fovea figure-ground relationships between an oncomingcar and the roadway. 72 There is no questionthat the headlights are highly visible, but wehypothesized that the figure-ground informa-tion about the speed and direction of the oncoming car is less readily availableto the driver without roadway illumination.A comparison of statistical likelihoods of vehicle-to-vehicle crashes at roadway inter-sections in Minnesota, with and without

R V P

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

1.0

0.8

0.6

0.4

0.2

0.0

Adult

R2 =0.78

Child

Mean identification time (s)

Figure 9 The relationship between relative visual per-formance (RVP) and mean identification time of life-sizetargets, black silhouettes of an adult and of a child, underdifferent types of cross-walk illumination (adapted fromBullough et al. 64 )





11/15

roadway lighting, to the visual performancepotential at these intersections, with andwithout roadway lighting, produces a transferfunction relating the incremental statisticalreduction in crashes to the incrementalincrease in visual performance. Figure 10shows the transfer function relating theincremental increase in RVP scores due toroadway lighting in Minnesota to the incre-mental statistical reduction in traffic crashesat night in Minnesota. 75 Although much morereinforcing experimental data need to begathered, it seems that the roadway lightingpractices in Minnesota provide, on average,about a 10% reduction in traffic crashes. Thissounds like a small number, but in fact, itprovides a quantitative foundation for decid-ing where and when roadway lighting shouldbe provided, as well as where and when itshould not be provided. Taking into accountthe costs of poles, luminaires, energy andmaintenance together with the benefits of avoiding property damage, injury and death,the value of a lighting system can be deter-mined for any type of intersection. As it turns

out, traffic volumes play a major role in thevalue of a roadway lighting system, wherevalue is defined as the safety benefits of roadway illumination divided by the fixedand operational costs to provide that illumin-ation. For busy urban roadways, roadwaylighting almost always provides a high value(i.e. the benefit/cost ratio is high) even if theimprovements in visual performance aresmall. In other words, a small benefit to alot of drivers can be highly valuable.Conversely, for rarely used, rural intersec-tions the value of lighting is much smaller.This is because there are so few people at theintersection that the benefits of illuminationgo unrealized.

I want to strongly emphasize again thatmany more reinforcing and converging stu-dies need to be conducted before the LightingResearch Center would recommend ourresults from Minnesota as the universalbasis for roadway lighting policy around theworld. Needed is converging evidence fromfield demonstrations, laboratory studies, add-itional statistical analyses of safety and light-ing from more states and countries, and,perhaps most importantly, long-term, longi-tudinal studies of the safety benefits of roadway lighting. Further, tests of the RVPmodel should also be conducted because it isone of the critical links in the logical chainconnecting roadway lighting and trafficsafety. Although I believe that the RVPmodel 23 has been validated as a method forassessing the visual benefits of roadwaylighting, so did Weston, Luckiesh andBlackwell believe their views of visual per-formance were valid. Karl Popper said, ineffect, that the only useful models in sciencewere those that were falsifiable by hypoth-esis testing. 77 From this perspective then,the predictive nature of the RVP modelmust be (and is) entirely open to falsification,if it is to have lasting significance for decidingwhether roadways should be illuminatedor not.

N i g h t t i m e c r a s

h r e

d u c

t i o n

15%

10%

5%

0%

Visual performance improvement(RVP score units)

0 0.5 1 1.5 2

R2 =0.93y=0.072x

Figure 10 Transfer function relating the calculated incre-mental improvements in relative visual performance(RVP) scores due to roadway illumination in Minnesotato the estimated night-time car-to-car crash reductionsdue to roadway intersection illumination in Minnesota. 75

RVP score values were used for the analysis whereby:RVP 0.9 3, 0.8 RVP 5 0.9 2, 0.7 RVP 5 0.8 1,RVP 5 0.7 0

10 MS Rea




12/15

5. Conclusions

I believe that long after the individuals on theintellectual battlefield retire, the precipitate of the struggle should be our collective, scientificunderstanding of natural phenomena. In thisbelief, there are two underlying points forcontemporary consideration. First, the prob-lems we will tackle as researchers will bechosen from within a social context, not, asmany suppose, in pursuit of pure science.Second, our understanding of natural phe-nomena may progress through hypothesistesting or that understanding may simply belost through neglect or ignorance. Ideally, asthe social context changes, the previousscientific discoveries inform the individualson the next intellectual battlefield and ourcollective understanding of natural phenom-ena gets broader and deeper. But, scientificprogress appears to be a matter of culture.Those cultures that accept dogma make noprogress at all, and those that do not have anappreciation or understanding of the historyof the science will not benefit from it.

The central battle of the 1970s over energyand recommended light levels has beenresolved, in some part because of the researchon visual performance begun in the 1930s inGreat Britain and in the United States thateventually culminated in the model of RVP. 23

Whether RVP serves society in the 21stcentury as a means for quantifying howroadway lighting can affect traffic safety willdepend largely upon whether contemporaryresearchers know the history of visual per-formance research in the 20th century.This assumes, of course, that society actually

cares how roadway lighting affects trafficsafety and wants to do something meaningfulabout it.

Acknowledgements

I would like to extend sincere thanks to mycolleagues at the Lighting Research Center

for their assistance in preparing this manu-script: John Bullough, PhD; MarianaFigueiro, PhD; Dennis Guyon and InesMartinovic.

References

1 Committee on Progress. Reaching for the sun.Illuminating Engineering 1959; 54: 19.

2 Coda FM. Energy notes: Letter to JC Sawhill,with response. Lighting Design and Application1974; 4: 6062.

3 Amick CL. Energyand our role as illumi-nating engineers. Lighting Design and Application 1974; 4: 3233.

4 Illuminating Engineering Society. Energyadvisory committee report. Lighting Designand Application 1974; 4: 1012.

5 Ross DK. Task lighting: Yet another view.Lighting Design and Application 1978; 8: 3743.

6 Commission Internationale de lE clairage. AUnified Framework of Methods for EvaluatingVisual Performance Aspects of Lighting, CIE-19 . Paris: CIE, 1972.

7 Federal Energy Administration. Proceedings of the Basis for Effective Management of Lightingand Energy Symposium. Washington, DC:Federal Energy Administration, 1972.

8 Crouch CL. Can we scientifically bridge thegap between the architect and the illuminatingengineer? Lighting Design and Application1972; 2: 3843.

9 Rowlands E, Loe DL, Waters IM, HopkinsonRG. Visual performance in illuminance of different spectral quality: 16th Session of theCommission Internationale de lE clairage .Barcelona, Spain. Paris: CommissionInternationale de lE clairage, 1971.

10 Boyce PR. Age, illuminance, visual perform-ance and preference. Lighting Research and Technology 1973; 5: 125145.

11 Loe DL, Waters IM. Visual Performance inIllumination of Differing Spectral Quality .London: Environmental Research Group,University College London, 1973.

12 McNeli s JF. Human performance: A pilotstudy. Journal of the Illuminating EngineeringSociety 1973; 2: 190196.





13/15

13 Smith SW, Rea MS. Proofreading under dif-ferent levels of illumination. Journal of theIlluminating Engineering Society 1978; 8:4752.

14 Hawkes RJ, Loe DL, Rowlands E. A note

towards the understanding of lighting quality.Journal of the Illuminating Engineering Society1979; 8: 111.

15 Smith SW, Rea MS. Relationships betweenoffice task performance and ratings of feelingand task evaluations under different lightsources and levels: Proceedings of the 19thsession of the Commission Internationale delE clairage . Paris: CIE 1980; 207211.

16 Stone PT, Clarke AM, Slater AI. The effectof task contrast on visual performanceand visual fatigue at a constant illuminance.Lighting Research and Technology 1980; 12:144.

17 Clear R, Berman S. Cost-effective visibility-based design procedures for general officelighting. Journal of the IlluminatingEngineering Society 1981; 10: 228236.

18 Rea MS. Visual performance with realisticmethods of changing contrast. Journal of theIlluminating Engineering Society 1981; 10:164177.

19 Smith SW, Rea MS. Performance of a readingtest under different levels of illumination.Journal of the Illuminating Engineering Society1982; 12: 2933.

20 Slater AI, Perry MJ, Crisp VHC. The appli-cability of the CIE visual performance model tolighting design: Light and Lighting 83,Proceedings of the 20th Session , Amsterdam,1983, pp. D114/14.

21 Rea MS. Toward a model of visual perform-ance: Foundations and data. Journal of theIlluminating Engineering Society 1986; 15:4157.

22 Rea M, Ouellette M. Visual performance using

reaction times. Lighting Research and Technology 1988; 20: 139153.

23 Rea M, Ouellette M. Relative visual perform-ance: A basis for application. LightingResearch and Technology 1991; 23: 135144.

24 Covington EJ. A Man from Maquoketa: ABiography of Matthew Luckiesh . EastCleveland, OH: Graphic CommunicationsOperation of GE Lighting at Nela Park, 1992.

25 Tinker MA. Illumination standards for effect-ive and easy seeing. Psychological Bulletin1947; 44: 435450.

26 Luckiesh M, Moss FK. The Science of Seeing .New York: D Van Nostrand Co., 1937.

27 Blackwell HR. A human factors approach tolighting recommendations and standards.Technology for Man 72: Proceedings of theSixteenth Annual Meeting , Los Angeles, 1719October 1972, pp. 441451.

28 Rea MS, Ouellette MJ. An Assessment of theBlackwell Visual Task Evaluator, Model 3X .Ottawa, ON: National Research Council,Division of Building Research, No. 160, 1984.

29 Blackwell HR. Effects of light source spectraldistribution upon visual functions. Annals of the New York Academy of Sciences 1985; 453:

340353.30 Redford R, ed. Lighting news. Illuminating

Engineering 1959; 54: 10A.31 Blackwell HR. The prescription of interior

lightingA progress report. Lighting Designand Application 1974; 4: 1216.

32 Dorsey RT. Interior lighting based on resourceoptimization. Lighting Design and Application1974; 4: 3642.

33 Beardsley CW, ed. Lighting news: FEAsenergy/lighting conservation program outlinedto IERI group. Lighting Design and

Application 1975; 5: 5253.34 Brandston H. A little light on sight. Lighting

Design and Application 1975; 5: 3538.35 Dorsey RT, Blackwell HR. A performance-

oriented approach to lighting specification.Lighting Design and Application 1975; 5:1327.

36 Blackwell HR. Energy conservation by select-ive lighting standards, graded in terms of taskand observer characteristics. Lighting Designand Application 1976; 6: 1729.

37 Weston H. The Relation Between Illumination

and Industrial Efficiency: The Effect of Size of Work . Joint Report of the Industrial HealthResearch Board and the Illumination ResearchCommittee. London: His Majestys StationaryOffice, 1935.

38 Weston H. The Relation Between Illuminationand Industrial Efficiency: The Effect of Brightness Contrast. Industrial HealthResearch Board of the Medical Research

12 MS Rea




14/15

Council. Report 87. London: His MajestysStationary Office, 1945.

39 Boyce PR. Human Factors in Lighting . NewYork NY: Macmillan, 1981.

40 Crouch CL. The relation between illumination

and vision. Illuminating Engineering 1945; 49:747784.

41 Blackwell HR. The problem of specifying thequantity and quality of illumination.Illuminating Engineering 1954; 49: 9397.

42 Redford R, ed. Lighting news. IlluminatingEngineering 1959; 54: 8, 10A.

43 Saxe JG. The Poetical Works of John GodfreySaxe . Boston MA: Houghton Mifflin, 1882.

44 Henderson RL, McNelis JF, Williams HG. Asurvey of important visual tasks in offices.Lighting Design and Application 1975; 5:

1825.45 McNelis JF, Williams HG, Henderson RL. A

survey and analysis of important visual tasksin officespart 2. Lighting Design and Application 1975; 5: 1623.

46 Boyce P. Movement under emergency lighting:The effect of illuminance. Lighting Researchand Technology 1985; 17: 5171.

47 Ouellette M, Rea M. Illuminance requirementsfor emergency lighting. Journal of theIlluminating Engineering Society 1989; 18:3742.

48 Yonemura GT. Criteria for recommendinglight levels. Lighting Research and Technology1978; 13: 113129.

49 Rea MS. Toward a model of visual perform-ance: A critical review of methodologies.Journal of the Illuminating Engineering Society1987; 16: 128142.

50 Redford R, ed. Specification of interiorillumination levels on the basis of performancedata (discussion and rebuttal of a paper byH Richard Blackwell published in June(1959) Illuminating Engineering ) 1959; 54:

775777.51 Smithsonian Institution. Lighting a Revolution .

Washington DC: National Museum of American History, 2009.

52 Cuttle C. Towards the third stage of thelighting profession. Lighting Research and Technology 2010; 42: 7393.

53 Tiller DK, Veitch JA. Perceived room bright-ness: Pilot study on the effect of luminance

distribution. Lighting Research and Technology1995; 27: 93101.

54 Fotios S, Gado T. A comparison of visualobjectives used in side-by-side matching tests.Lighting Research and Technology 2005; 37:

117131.55 Rea MS, Bullough JD, Akashi Y. Several

views of metal halide and high pressure sodiumlighting for outdoor applications. LightingResearch and Technology 2009; 41: 297320.

56 Figueiro MG. A proposed 24 h lighting schemefor older adults. Lighting Research and Technology 2008; 40: 153160.

57 Illuminating Engineering Society of NorthAmerica. American National Standard forRoadway Lighting . New York NY: IESNA,2000.

58 Boyce PR, Rea MS. Plateau and escarpment:The shape of visual performance: Proceedings of the CIE 21st Session , Venice, 1987, pp. 8285.Vienna: Commission Internationale delE clairage.

59 Rea MS, Boyce PR, Ouellette MJ. On time tosee. Lighting Research and Technology 1987;19: 101103.

60 Goodspeed CH, Rea MS. The significance of surround conditions for roadway signs.Journal of the Illuminating Engineering Society1999; 28: 164173.

61 Eklund N, Boyce P, Simpson S. Lighting andsustained performance: Modeling data-entrytask performance. Journal of the IlluminatingEngineering Society 2001; 30: 126141.

62 Schnell T, Yekhshatyan L, Daiker R. Effectof luminance and text size on informationacquisition time from traffic signs.Transportation Research Record 2009; 2122:5262.

63 Skinner NP, Bullough JD. Influence of intelli- gent vehicle headlamps on pedestrian visibility inroundabouts: 9th International Symposium on

Automotive Lighting , Darmstadt, Germany,2011; Munchen: Herbert Utz Verlag.

64 Bullough JD, Rea MS, Zhang X. Evaluation of visual performance from pedestrian crosswalklighting: Transportation Research Board 91stAnnual Meeting , Washington, DC, 2226January 2012, Paper no. 12-3348.

65 Dillon RF, Pasini IC, Rea MS. Survey of visual contrast in office forms: 21st Session of the





15/15

Date post:	04-Jun-2018
Category:	Documents
Upload:	tommyc1024
View:	219 times
Download:	0 times

Lighting Research and Technology 2012 Rea 1477153512441163

Documents