Do light-emitting diode cap lamps 


enable improvements in miner safety?
 

J. Sammarco, m.a. reyeS and S. GallaGher 

J. Sammarco, M.A. Reyes and S. Gallagher are senior 

research engineer, research engineer and senior research 

scientist, respectively, with the national Institute for occupational Safety and health (nIoSh), Pittsburgh, Pa. 

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Abstract 

Proper illumination is critical to a miner’s ability to detect 

hazards in underground mines. Moving hazards are often 

located in the miner’s peripheral field-of-view,while slip/trip/ 

fall hazards are often located in the forward field-of-view. 

The objective of the research described in this paper was to 

determine if light-emitting diodes (LEDs) improve visual 

performance as compared to traditional incandescent (INC) 

cap lamps.The research presented focuses on comparative 

studies of a National Institute for Occupational Safety and 

Health (NIOSH) prototype LED, a commercial LED and 

an INC camp lamp. Thirty subjects participated in these 

studies,with ten subjects in each of the following age groups: 

18 to 25 years, 40 to 50 years and 51+ years old.Visual performance was quantified by the subjects’ speed and accuracy 

in detecting hazards, while visual performance for disability 

glare was quantified by the use of contrast sensitivity tests. 

Results suggest that LEDs with a visible spectrum containing a higher concentration of the shorter wavelengths can 

enable visual performance improvements with respect to 

disability glare, the detection of moving hazards in the peripheral field-of-view and the detection of floor hazards in 

the forward field-of-view.The NIOSH prototype LED cap 

lamp provided the best visual performance improvements 

for the older age groups in every test. 

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Introduction 

An underground mine is a dynamic environment that consists 

of confined spaces, low reflectivity 

surfaces, low visual contrast and numerous glare sources. These factors 

ultimately pose significant impedi

ments to a miner’s ability to per

form his or her job safely.Typically, a 

miner’s cap lamp is the primary and 

most important source of light for 

detecting hazards posed in the form of falls of ground, 

machinery-related pinning and striking incidents, and 

slipping and tripping hazards. Accordingly, illumination 

plays a critical role in an underground miner’s safety 

because miners depend, most heavily, on visual cues to 

detect these potential hazards (Cornelius et al., 1998). It 

can often prove difficult for miners to detect such haz

ards because objects associated with slip, trip and fall 

hazards are typically of very low contrast and reflectiv-

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ity, and extremely noisy mining environments can mask audible cues 

given by approaching machinery. 

Glare is another factor to consider, 

as it can impede a miner’s ability to 

identify hazards and perform his or 

her job safely. Accordingly, proper 

design of mine illumination systems 

emerges as a critical factor to con

sider for miner safety. 

The main objective of the 

NIOSH research presented in this paper was to exam

ine whether visual performance improvements might 

be obtained through the manipulation of a cap lamp’s 

spectral content distribution. Specifically, the subjects’ 

visual performance was compared when using cool-white 

light-emitting diode (LED) technologies that have a 

higher concentration of short-wavelength energy versus 

traditional warm-white incandescent bulbs that emit 

a “yellowish” light due to the higher concentration of 

longer-wavelength energy. Recent nighttime driving and 

underground mining research has indicated that in lowlight (mesopic) conditions, increased short-wavelength 

spectral content can improve visual performance (Van 

Derlofske and Bullough, 2003; Van Derlofske et al., 

2005; Sammarco and Lutz, 2007; Sammarco et al., 2008a, 

2008b).A secondary objective was to determine the role 

of aging on visual performance in mesopic conditions 

with respect to these lighting technologies. The physiology of the human eye is such that visual performance 

degrades as a person ages. These physiological changes 

include reduced pupil size, cloudier lenses and reduc

tion in the amount of rod photoreceptors that play a 

dominant role in vision for low-light conditions may all 

have a significant impact on visual performance as light 

levels decrease.This emerged as another critical factor to 

consider during these studies due to the age of U.S. coal 

mine workforce, which currently averages approximately 

43 years. 

This paper summarizes the results of three experi

ments designed to investigate these factors. Experiments 

1 and 2 were designed to examine the ability to detect 

peripheral motion and slip, trip and fall hazards, respec

tively, using an LED cap lamp as compared with the more 

commonly used incandescent cap lamp. Experiment 3 

was designed to evaluate discomfort and disability glare 

produced by LED and incandescent cap lamps. 

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General methodology 

Subjects. The same human subjects, 24 male and six 

female, participated in all three experiments. Subjects 

were recruited from NIOSH personnel at the Pittsburgh 

Research Laboratory (PRL). None were specifically in

volved with the cap lamp research. Most of the subjects 

were not familiar with miner cap lamps, or they had used 

them infrequently.The decision not to use miners as subjects was due to possible expectancy biases that could 

confound the empirical data. For example, miners might 

determine that the blue-white light from an LED cap 

lamp is very different from the yellowish light of an in

candescent cap lamp; thus, a negative bias could exist 

because they are not accustomed to the LED light color, 

or a positive bias could exist if the person perceives some

thing new as better. 

Age was an independent variable for each experi

ment. Three age groups, each consisting of ten subjects, 

were established: Group A = 18 to 25 years of age, Group 

B = 40 to 50 years of age; and Group C = 51 years of age; 

and over. The average age of the participants was 42.5 

years, which is representative of the average U.S. coal 

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miner’s age of 43 years. Screening of 

subjects included extensive vision test

ing for distance visual acuity, contrast 

sensitivity, color vision deficiency and 

peripheral vision. Screening was fol

lowed by a detailed description of the 

experiments to be conducted as well as 

a consent form that informed subjects 

about their right to withdraw freely 

from the research at any time without 

penalty. 

Cap lamps. The experiments were 

designed to compare three cap lamps 

that served as the independent vari

ables for each study.The first cap lamp 

was a Mine Safety and Health Administration (MSHA)-approved cap lamp 

designed to use a single incandescent 

bulb as the primary light source. This 

was selected as the experiments’ refer

ent light source. The second cap lamp 

was a commercial, MSHA-approved, 

cap lamp designed to use a single, 

phosphor-white LED as the primary 

light source. The third cap lamp was a 

laboratory prototype that was jointly 

developed by NIOSH and the Lighting 

Research Center of Rensselaer Poly

technic Institute. This prototype was 

designed to use two phosphor-white 

LEDs as the primary light source. The 

electrical data recorded for each cap 

lamp is listed in Table 1.

Table 1 

Cap lamp electrical and photometric data. 

Electrical 

characteristics 

Photometric 

characteristics 

 Supply Supply 

 voltage, current, 

camp lamp Vdc amps 

Supply Peak correlated 

power, wavelength, color temp., 

watts nm K 

INC 

Commercial LeD 

Prototype LeD 

6.1 

6.1 

12.0 

0.63 

0.42 

0.113 

3.84 

2.56 

1.36 

780 

448 

444 

2,880 

5,855 

6,844 

 Additionally, 

each cap lamp was characterized with 

respect to its spectral power distri

bution (SPD), depicted in Fig. 1. 

Figure 1 

Spectral power distributions (SPDs) for cap lamps used. 

Be

cause initial illuminance distribution 

measurements revealed significant 

variations in the light output, the ap

plication of diffusion filters was necessary to normalize the light output for 

each cap lamp. For example, preliminary measurements 

indicated that the illuminance of certain objects was 42% 

greater with the prototype LED cap lamp than with the 

incandescent cap lamp. Controlling the illuminance dis

tributions throughout the experiments ensured that the 

lighting research was contained to the spectral content 

of the cap lamps rather than a combination of several 

underlying factors that would confound the data. The 

diffusion filters successfully maintained a more uniform 

illuminance distribution among cap lamps. 

Mine illumination laboratory. Experiments were 

conducted at the Mine Illumination Laboratory (MIL) 

located at NIOSH Pittsburgh Research Laboratory. 

Measuring 4.88 m (16 ft) wide by 2.13 m (7 ft) high, this 

simulated underground coal mine environment is fully 

equipped with data acquisition and control systems, with 

networked computers and with safety equipment and 

signage essential to accommodate human subject test

ing. MIL was designed to match the texture, color and 

reflectivity of surfaces commonly found in underground 

coal mines. 

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Observation station. It was important to have each 

subject be at a fixed, known coordinate with respect to 

each test apparatus and to have each subject’s position 

fixed so that their point of view was the same regardless 

of their body size. This eliminated data confounding 

from variations in the subjects’ point of view. Hence, 

NIOSH personnel designed and constructed an obser

vation station (Fig. 2) to enable each subject to be tested 

at an eye height of 1.651 m (65 in.).

Figure 2 

The observation station used for all experiments. 

This eye height, with 

reference to the floor, was based on the 50th percentile 

standing male (USDOT, FAA, 2003). Controlled us

ing electric actuators, the seat was designed to rise 200 

mm (7.9 in.) from the lowest position to its highest to 

accommodate testing of subjects ranging from the 5th 

percentile female to the 95th percentile male. 

The height of the miner’s helmet was independently 

adjustable from the seat height to accommodate varying 

torso lengths, which ranged from 686 to 848 mm (27.0 to 

33.4 in.). A swivel was incorporated into the station to 

allow the seat to rotate 360°, thus enabling the subject 

to face multiple test apparatuses without leaving the ob

servation station. This feature reduced the overall test

ing time enabling the researchers to minimize subject 

fatigue and boredom, limiting the subject’s exposure to 

potential trip or fall hazards if they were to travel to and 

be seated on a separate observation station for each test. 

The observation station and all of its components were 

painted flat black to eliminate any reflection of light and 

to prevent distractions during testing. 

General procedures. Each subject was given a mini

mum of 15 minutes to adapt to the darkened environment 

of the MIL. Next, a subject was seated on the observation 

station and adjustments were made such that each per

son had the same eye height of 1.651 m (65 in.) from the 

floor. While seated, the subjects wore a hardhat rigidly 

mounted to the observation station to help maintain a 

consistent head and cap lamp position. Eye protection 

was provided similar to that worn underground.The sub

jects were provided hearing protection to avoid possible 

auditory cues that could affect outcomes. Additionally, 

a sound track of underground mining operations was 

played during the tests to negate possible auditory cues 

and to help create a more realistic environment. Once the 

subjects were positioned and the equipment properly ad

justed, the test procedures were explained to the subjects. 

Warm-up (practice) sessions were initially conducted 

to help subjects learn how to conduct the tests and to 

become familiar and comfortable with the test apparatus 

and procedures. 

Experiment 1: Peripheral motion detection 

Experimental design. A 3 x 3 x 3 (age group x light 

source x target location) split-split plot design was used in 

this study (Kirk, 1995). Subjects represented whole-plots, 

and the whole-plot factor was age group. There were 

three age group categories: Group A = 18 to 25 years old; 

Group B = 40 to 50 years old; Group C = 51+ years old. 

The light source was the split-plot factorial and also had 

three levels consisting of: a commercial LED cap lamp, 

a commercial incandescent cap lamp and a prototype 

LED cap lamp. High contrast, white circular targets were 

positioned at -20°, 40° and 50° (Fig. 3) off axis. 

Figure 3 

Experimental layout for Experiment 1: Peripheral motion 

detection (figure not to scale). 

The angle 

of the target location was the split-split plot factorial.Two 

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primary dependent measures were used to examine the 

effects of the independent measures listed above.The two 

primary dependent measures were detection time, i.e., 

time to detect target movement, measured in millisec

onds (ms), and number of target movements missed. 

Apparatus. The peripheral motion apparatus was designed and built by NIOSH to perform the data acqui

sition and control (DAC) throughout the experiment. 

The system’s main components were a microcontroller, 

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a flip-dot matrix target, DAC software and high-contrast 

(white) circular targets connected to dc-powered mo

tors. The system’s input, controlled by the subjects being 

tested, was a computer mouse. Subjects would depress 

the mouse button causing an electrical signal to the mi

crocontroller to initiate the test.The microcontroller then 

activated a flip-dot matrix, located at zero degrees, which 

served as a visual tracking target. The purpose of this visual tracking target was to draw a subject’s focus and fix 

their eye orientation to the center. In doing so, the subject 

would be forced to use their peripheral vision to detect 

motion rather than using direct line of sight. 

The control system accessed one of four different 

software versions compiled to vary the sequence in which 

the three circular targets were sequentially activated.The 

circular targets, positioned at -20°, 40° and 50° off-axis, 

were rotated by dc motors mounted on tripods. Because 

the dc motors emitted noise that could have confounded 

the results, it was necessary to mask the noise by using ear 

protection and background sounds of mining equipment 

in operation. This eliminated a subject’s ability to use 

the auditory cues to identify which target was activated. 

The data acquisition process consisted of a time-stamped 

spreadsheet macro that recorded the cap lamp used, the 

software version used, the target location sequence and 

the peripheral motion detection reaction time. 

Procedures. This experiment consisted of five trials, 

two of which were practice sessions. The three other trials consisted of experimental trials where the type of 

cap lamp was varied. Subjects were encouraged to ask 

questions if any part of the instructions were unclear.The 

subjects were then instructed to keep their eyes focused 

on the center flip-dot matrix target in front of them dur

ing this entire experiment.They were handed a computer 

mouse and were briefed on the operation of the mouse. 

Holding down the left mouse button started the test.The 

subjects were to release the depressed mouse button to 

indicate when they saw a circular target rotate. Reac

tion time was measured as time the circular target was 

initially activated to the time the subject released the depressed mouse button. A reaction time of 4.2 seconds or 

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above would be recorded as a missed 

target. In addition to varied sequences, randomization in time delays and 

counterbalancing of tests were imple

mented to prevent learned behavior 

from impacting validity of results. 

Results and discussion. A split-split 

plot analysis of variance (ANOVA) 

was used to evaluate whether there 

were significant differences for the independent variables.All three main ef

fects (age group, angle and cap lamp) 

significantly affected detection time; 

no interactive effects were detected. 

Age group had a significant effect on 

detection time (F2,27 = 5.38, p < 0.05). 

Group A (younger subjects) had sig

nificantly faster detection times than 

Group B subjects. Detection time dif

ferences were not statistically signifi

cant between Groups B and C. The 

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target angle significantly affected detection time (F2,154 

= 60.14, p < 0.001). The 40° target resulted in about a 

16% increase in detection time compared to the -20° 

target, while the 50° target had a 76% increase in detection time.The prototype LED enabled significantly faster 

detection times than the commercial LED (F2,54 = 4.62, 

p < 0.05). On average, post hoc tests indicated that the 

prototype LED resulted in 11% and 15% faster detec

tion times than the INC and commercial LED cap lamps, 

respectively. No statistically significant difference in per

formance was found between the INC and commercial 

LED cap lamps. The prototype LED cap lamp’s visible 

spectrum contains more of the shorter wavelengths than 

the commercial LED cap lamp. The differences between 

the LED cap lamps are especially notable at 555 nm, 

where the commercial LED cap lamp has a much greater 

proportion of longer wavelengths in comparison to the 

prototype LED cap lamp. The lack of an interaction between age and light source indicates that the prototype 

LED cap lamp provides similar benefits to all age groups 

in terms of improving the ability to detect moving objects 

in the peripheral visual field. This benefit, however, may 

be more important for middle-aged and older workers. 

Experiment 2: Floor hazard detection 

Experimental design. A within-subjects design was 

employed in this study. Presentation of cap lamps were 

randomly assigned to subjects and a restricted randomiza

tion was used for stimulus order presentation within cap 

lamps. The independent variables were the four object 

patterns: near field, far field and two combinations of near 

field and far field. The dependent variables, quantifying 

visual performance, remained the same as Experiment 1. 

Experimental layout. The general layout is depicted 

by Fig. 4.

Figure 4	 

Experimental layout for Experiment 2: Floor hazard detection (figure not to 

scale). 

A motorized curtain was installed 0.91 m (3.0 ft) 

in front of the observation station to prevent the subject 

from gaining an advantage in finding the objects while the 

researcher switched object location patterns.This curtain 

was connected to a microcontroller programmed to control the curtain and time the duration of each test. Two 

location categories were established for this experiment: 

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near-field at 1.83 m (6.0 ft), about the 

distance of two strides for the average 

male, and far-field at 3.66 m (12.0 ft). 

The far-field location is a more com

mon visual attention location for a 

walking person, and it is a location of 

higher illuminance given the cap lamp 

mounting on the miner’s helmet.Table 

2 lists the near field and far-field illu

minances. 

Table 2 

Near and far-field illuminances. 

 

 commercial Prototype 

incandescent LED LED 

average near-field illuminance (lux) 1.28 1.17 1.17 

average far-field illuminance (lux) 1.27 1.49 1.26 

Overall average illuminance (lux) 1.28 1.34 1.22 

Each object was 64 mm (2.5 

in.) long with a 33 mm (1.3 in.) outer diameter. The ob

jects were painted a dark color such that they would have 

a very low contrast (-0.11 to 0.09) and a reflectivity very 

similar to an object that was coated with the material on a 

mine floor. Four object location patterns were presented 

to each subject: two objects in the far and near field; two 

objects in near field; two objects in the far field and two 

objects in the far and near field. 

Procedures. The procedure was to close the black, 

electrically-powered curtain and arrange objects accord

ing to the corresponding object patterns selected for 

each subject. The subjects were instructed to point at 

each object using a laser pointer and count it out loud. 

When the subject was ready, the curtain was opened and 

the PC-based data-acquisition system started recording 

time. Two researchers determined that an object was 

detected the instant the subject pointed the laser pointer 

at the target and confirmed it audibly by counting. The 

curtain was closed after a ten second period and the Excel spreadsheet macro recorded the time for which the 

last object was accounted for or the ten-second period 

had expired. 

Results and discussion. Results of the Cox regression 

forward selection process indicated that object pattern 

was the most influential factor in terms of detection time, 

followed by the type of cap lamp used and then the age 

group. No significant interactions were detected and the 

proportional hazards assumption was met in all cases. In 

the comparison of cap lamp effects, both LED cap lamps 

(prototype and commercial LED) led to more rapid de

tection of objects compared to the traditional INC cap 

lamp (p < 0.001). Comparisons of cap lamp performance 

demonstrate the clear superiority of the LED cap lamps 

for the current task. Compared to the incandescent cap 

lamp, currently standard in the mining industry, the LED 

cap lamps resulted in detection times that were, on average, more than 1.5 seconds faster.The prototype LED cap 

lamp resulted in 23.7% faster detection times than the 

INC cap lamp and 21.9% faster detections times than the 

commercial LED cap lamp.The mean detection time and 

standard error for the INC cap lamp was 7.447 sec. 0.5999 

SE. The prototype LED resulted in slightly faster detec

tion time than the commercial LED cap lamp; however, 

the difference was not statistically significantly. 

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Experiment 3: Discomfort and disability glare 

Experimental design. A 3 x 3 (age group x cap lamp) 

split-plot factorial design was used.The age group represented the whole-plot factor and light source represented 

the split-plot factor. The interaction of age group and 

light source was part of the split-plot analysis. The de

pendent variables were the subjective discomfort glare 

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ratings (qualitative, De Boer scale 1 through 9) and the 

contrast sensitivity score for disability glare. The presentation order for cap lamps was counterbalanced, where 

replication 1 was the baseline presentation order and 

replication 2 was the reversed presentation order. 

Apparatus. The experimental layout for the glare experiment (Fig. 5) was set up to seat each subject facing to

ward the two charts used throughout the experiment.

Figure 5 

Experimental layout for Experiment 3: Discomfort and disability glare (figure not to scale). 

The 

De Boers scale and the Mars letter contrast sensitivity 

chart were both used to investigate the degree of discom

fort and disability experienced by subjects when exposed 

to the glare produced by each cap lamp. These charts 

were located at zero degrees, at a height equal to that of 

the subject’s eye height. The cap lamps were positioned 

1.83 m (72 in.) away from the test subject at an angle of 

-10° off axis. The cap lamps were pointed directly at the 

subject to simulate glare from another miner’s cap lamp. 

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Procedures. This experiment consisted of two parts. 

The first part was designed to obtain a subjective rating of 

discomfort for each of the three cap lamps used. Subjects 

were instructed to focus their attention to a rating scale 

located directly in front of them while a glare source was 

adjusted. Using the De Boer scale, which is a commonly 

accepted method for measuring discomfort glare, the 

subjects were asked to rate the glare source located 10 ̊ 

off-axis. The De Boer’s scale is a nine-point subjective 

scale, where a rating of 1 is considered “unbearable” and 

a rating of 9 was considered “just noticeable.” The rat

ing given by each subject is recorded using a customized 

software database. 

After the completion of the discomfort test, the dis

ability test was administered. This test was designed to 

determine the degree to which the glare sources would 

impair a person’s vision. The Mars letter contrast sensi

tivity chart was used to measure visual performance with 

respect to contrast sensitivity. Visual performance was 

quantified by a subject’s ability to correctly identify let

ters of varying contrast while a glare source was directed 

towards the subject’s eyes.The test would conclude when 

the subject missed two consecutive letters, at which point 

the contrast sensitivity was calculated. 

Results and discussion. ANOVA was used to evalu

ate whether there were significant differences for the 

contrast sensitivity tests and the De Boer ratings, respectively. De Boer ratings were treated as an interval vari

able, as distances between various measurements on the 

scale were considered meaningful. Parametric statistical 

tests (such as F tests) may be applied to De Boer ratings, 

an approach that was utilized, for example, in a study 

on disability glare by the Federal Highway Administra

tion (Porter et al., 1995). Results indicated a significant 

interaction was present between age group and cap lamp 

for contrast sensitivity. Additional statistical analysis in

dicated that the prototype LED cap lamp resulted in 

significantly better contrast sensitivity scores in the older 

age group compared to the other cap lamps, whereas the 

youngest age group showed no difference in contrast sen

sitivity between any of the cap lamps (FS 4,108 = 10.091, p 

< 0.05).The commercial LED and incandescent cap lamp 

indicated no statistically significant difference in contrast 

sensitivity across age groups (FS 2,108 = 1.10, p > 0.05). 

The qualitative De Boer ratings of discomfort glare were 

affected by age group (F 2,45 = 9.41, p < 0.001) but not by 

the cap lamp. Analysis of the mean De Boer ratings for 

each cap lamp suggests that ratings were highest (a higher 

rating means less discomfort glare) for the prototype 

LED than for the other cap lamp; however, this qualitative assessment did not achieve statistical significance 

among the cap lamps. It is apparent from the findings of 

this study that spectral content of light from the LED cap 

lamps do not appear to increase discomfort glare, and 

that only the prototype LED cap lamp has the poten

tial to significantly improve safety by reducing disability 

glare, especially among older workers who are most susceptible to glare and its effects. For older workers, there 

was a 45% improvement in contrast sensitivity compared 

to the other light sources studied. Contrast sensitivity is 

an important aspect of visual performance especially in 

underground coal mines that are typically a low-contrast 

environment. Additionally, it is a critical factor for many 

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work tasks, so implementation of the prototype cap lamp 

design could provide a major benefit for the aging mining 

population with respect to disability glare. 

General discussion 

Given the conditions of this study, the results sug

gest that LEDs with more of the shorter wavelengths, 

such as found with the prototype LED cap lamp, may 

offer improved peripheral motion detection, floor hazard 

detection and reduce disability glare for older workers. 

These results appear to be similar to results of recent 

research indicating that, at mesopic conditions, a shortwavelength spectral content can improve visual perfor

mance. Note that the prototype LED cap lamp had the 

shortest wavelengths, and it enabled the best results in 

all three experiments. The commercial LED cap lamp 

did not perform as well as the prototype LED cap lamp 

for Experiment 1: peripheral motion detection. Thus, 

the results suggest that not all LED caps lamps, given 

the conditions of this study, will enable significant visual 

performance improvements. 

The results of the visual performance comparisons 

between LED and INC cap lamps provide important 

data for improving the design of future cap lamps and 

should positively affect the safety of employees in the 

underground mining industry. Such a benefit could prove 

to be very important for the health and safety of the underground miner. For example, a reduced capability in 

peripheral motion detection or perception could make it 

difficult for miners to detect moving machinery or could 

cause them to misjudge the speed that a machine is moving towards them. Any improvement in the ability to 

perceive objects moving in the periphery will convey an 

advantage in terms of being able to avoid contact with 

moving machinery. 

Lastly, this study was limited to new cap lamps that 

functioned at optimal performance. A larger and more 

detailed study is needed to determine the effects of the 

real-world conditions of light source aging and battery 

discharge over a typical mine shift.The authors’ previous 

research has indicated that there are significant differ

ences between INC and LED cap lamps for real-world 

conditions and that LEDs have significant advantages 

(Sammarco et al., 2008b). Specifically, the light output 

of a new INC cap lamp with a nickel-hydride battery 

decreased about 35% after 8 hours, while a new LED cap 

lamp with the same battery had a light output decrease 

of about 3%.After aging the INC and LED,the light out

puts decreased an additional 35% and 3%, respectively. 

Additionally, changes in spectral power distributions 

of the INC and LED camp lamps were evaluated for a 

10-hour battery discharge.The LED had very little spec

tral shift, while the INC had a substantial shift to less of 

the shorter wavelengths. Generally, visual performance 

increases with increasing light, and it increases when 

the light contains more of the shorter wavelengths; thus, 

it is reasonable to expect that the visual performance 

improvements, enabled by LEDs, would be even greater 

under real-world conditions. 

Acknowledgments 

The studies described in this paper were conducted 

with the assistance from J. Bartels,T. Lutz,A. Mayton, M. 

Nelson and J. Srednicki of NIOSH PRL.Vision testing of 

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subjects was conducted by M.A. Rossi, R.N. of NIOSH 

PRL. 

Disclaimer 

The findings and conclusions in this report have not 

been formally disseminated by the National Institute for 

Occupational Safety and Health and should not be construed to represent any agency determination or policy. 

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