DO LIGHT-EMITTING DIODE CAP LAMPS ENABLE IMPROVEMENTS IN MINER SAFETY? 

J. Sammarco, NIOSH, Pittsburgh, PA 

M. A. Reyes, NIOSH, Pittsburgh, PA 

S. Gallagher, NIOSH, Pittsburgh, PA 

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; ten subjects in each of the age 

groups: 18 to 25 years, 40 to 50 years, and 51+ years. 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. 

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. 

INTRODUCTION 

An underground mine is a dynamic environment that consists of 

confined spaces, low reflective surfaces, low visual contrasts, and 

numerous glare sources. These factors, ultimately, pose significant 

impediments to a miner’s ability to perform their jobs 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 since 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 hazards because 

objects associated with slip, trip, and fall hazards are typically of very 

low contrast and reflectivity, and audible cues given by approaching 

machinery can be masked by extremely noisy mining environments. 

Glare is another factor to consider, as it can impede a miner’s ability to 

identify hazards and perform their job safely. Accordingly, proper 

design of mine illumination systems emerges as a critical factor to 

consider for miner safety. 

The main objective of the NIOSH research presented in this paper 

was to examine 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 low-light (mesopic) conditions, increased shortwavelength spectral content can improve visual performance (Van 

Derlofske and Bullough, 2003; Vanderlofske et al., 2005; Sammarco 

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

which include reduced pupil size, cloudier lenses, and reduction in the 

amount of rod photoreceptors that play a dominant role in vision as 

light levels decrease, 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 experiments 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 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. 

GENERAL METHODOLOGY 

Subjects 

The same human subjects, twenty-four male and six female, 

participated in all three experiments. Subjects were recruited from 

NIOSH personnel at the Pittsburgh Research Laboratory (PRL). None 

were specifically involved with our 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 incandescent 

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 something new as better. 

Age was an independent variable for each experiment. Three age

groups were established and each had ten subjects: 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 of age which is closely representative of the average U.S. coal 

miner’s age of 43 years. Screening of subjects included extensive 

vision testing for distance visual acuity, contrast sensitivity, color vision 

deficiency, and peripheral vision. Screening was followed 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 variables 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’ referent 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 

Polytechnic 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. Additionally, each cap 

lamp was characterized with respect to its spectral power distribution 

(SPD) and is depicted in Fig. 1. Because initial illuminance distribution 

measurements revealed significant variations in the light output, the 

application 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 distributions 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. 

Table 1. Cap lamp electrical and photometric data. 

Cap Lamp 

Electrical Characteristics Photometric 

Characteristics 

Supply 

Voltage 

(Vdc) 

Supply 

Current 

(amps) 

Supply 

Power 

(watts) 

Weak 

wavelength 

(nm) 

Correlated 

color 

temperature 

(CCT) (K) 

INC 6.1 0. 63 3.84 780 2880 

LED 6.1 0.42 2.56 448 5855 

Prototype 

LED 12.0 0.113 1.36 444 6844 

Figure 1. Spectral Power Distributions (SPDs) for cap lamps used.

Mine Illumination Laboratory 

Experiments were conducted at the Mine Illumination Laboratory 

(MIL) located at NIOSH Pittsburgh Research Laboratory. Measuring 

4.88 meters (m) wide by 2.13 m high, this simulated underground coal 

mine environment is fully equipped with data acquisition and control 

systems, networked computers, and safety equipment and signage 

essential to accommodate human subject testing. MIL was designed to 

match the texture, color, and reflectivity of surfaces commonly found in 

underground coal mines. 

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 observation station (Fig. 2) to enable 

each subject to be tested at an eye height of 165.1 centimeters (cm). 

This eye height, with reference to the floor, was based on the 50th 

percentile standing male (USDOT, 2003). Controlled using electric 

actuators, the seat was designed to rise 20 cm 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 68.6 cm to 

84.8 cm. A swivel was incorporated into the station to allow the seat to 

rotate 360 degrees thus enabling the subject to be placed in front of 

multiple test apparatuses without leaving the observation station. This 

feature reduced the overall testing time that enabled us to minimize 

subject fatigue and boredom, and it limited 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 a flat black color to eliminate the 

reflection of any light and to prevent distractions during testing. 

Figure 2. The observation station used for all experiments. 

General Procedures 

Each subject was given a minimum 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 person 

had the same eye height of 165.1 cm 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 subjects were 

provided hearing protection to avoid possible auditory cues which 

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 adjusted, 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 

Method 

Experimental Design: A 3 x 3 x 3 (age group, light source, 

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 = 18-25 

yrs. old; Group B = 40-50 yrs. old; Group C = 51+ yrs. 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. The angle of the 

target location was the split-split plot factorial. Two primary dependent 

measures were used to examine the effects of the independent 

measures listed above. These dependent measures were: 1) detection 

time, in milliseconds (ms), to detect target movement; 2) number of 

target movements missed. 

Apparatus: The peripheral motion apparatus was designed and 

built by NIOSH to perform the data acquisition and control (DAC) 

throughout the experiment. The system’s main components were a 

microcontroller, a flip-dot matrix target, DAC software, and highcontrast (white) circular targets connected to dc-powered motors. The 

system’s input, controlled by subjects being tested, was a computer 

mouse. Subjects would depress the mouse button causing an electrical 

signal to the microcontroller to initiate the test. The microcontroller then 

activated a flip-dot matrix, located at 0°, 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. 

Figure 3. Experimental layout for Experiment 1: Peripheral Motion 

Detection (figure not to scale). 

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 which 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 different 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 during 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. Reaction 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 above would be recorded as a missed target. In 

addition to varied sequences, randomization in time delays and 

counterbalancing of tests were implemented 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 effects (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 significantly faster detection times than Group B subjects. 

Detection time differences were not statistically significant between 

Group B and Group C. The 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 the average, post hoc tests indicated that 

the prototype LED resulted in 11% and 15% faster detection times than 

the INC and commercial LED cap lamps, respectively. No statistically 

significant difference in performance 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 

detecting 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 

Method 

Experimental Design: A within-subjects design was employed in 

this study. Presentation of cap lamps were randomly assigned to 

subjects and a restricted randomization was used for stimulus order 

presentation within cap lamps. The independent variables were the 4 

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.

A motorized curtain was installed .91 m 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: near-field 1.83 meters (m), about 

the distance of two strides for the average male, and far-field 3.66 m, 

far-field location that is a more common 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 illuminances. Each object was 6.4 cm long with a 3.3 cm outer 

diameter. The objects 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 the mine floor. Four 

object location patterns were presented to each subject: (a) two 

objects in the far and near field; (b) two objects in near field; (c) two 

objects in the far field; (d) two objects in the far and near field. 
Figure 4. Experimental layout for Experiment 2: Floor Hazard 

Detection (figure not to scale). 

Table 2. Near and Far-Field Illuminances. 

Incandescent Commercial 

LED 

Prototype 

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 

Procedures: The procedure was to close the black, electrically 

powered, curtain and arrange objects according 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 PCbased data acquisition system started recording time. Two researchers 

determined 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 

commercially LED) led to more rapid detection 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 that is 

current 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 detection time than the commercial LED 

cap lamp; however, the difference was not statistically significantly. 

EXPERIMENT 3: DISCOMFORT AND DISABILITY GLARE 

Method 

Experimental Design: A 3 x 3 (Age Group x Cap Lamp Glare 

Source) 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 dependent variables were the 

subjective discomfort glare ratings (qualitative, De Boer scale 1-9) and 

the contrast sensitivity score for disability glare. The presentation order 

for cap lamps was counterbalanced where rep 1 was the baseline 

presentation order and rep 2 was the reversed presentation order. 

Apparatus: The experimental layout for the glare experiment 

(Fig. 5) was set up to seat each subject facing toward the two charts 

used throughout the experiment. The De Boers scale and the Mars 

Letter Contrast Sensitivity chart were both used to investigate the 

degree of discomfort and disability experienced by subjects when 

exposed to the glare produced by each cap lamp. These charts were 

located at 0°, at a height equal to that of the subject’s eye height. The 

cap lamps were positioned 183 cm (72 in) away from the test subject, 

at an angle of -10 degrees off axis. The cap lamps were pointed 

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

Figure 5. Experimental layout for Experiment 3: Discomfort and 

Disability Glare (figure not to scale). 

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’s 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 9-point subjective scale where a rating of 1 was considered 

“unbearable” and a rating of 9 considered “just noticeable”. The rating 

given by each subject was recorded using a customized software 

database. 
After the completion of the discomfort test, the disability 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 Sensitivity chart was used to measure visual performance 

with respect to contrast sensitivity. Visual performance was quantified 

by a subject’s ability to correctly identify letters 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 evaluate whether 

there were significant differences for the contrast sensitivity tests and 

the De Boer ratings, respectively. De Boer ratings were treated as an 

interval variable, 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 utilized, for 

example, in a study on disability glare by the Federal Highway 

Administration [Porter et al., 1995]. Results indicated a significant 

interaction was detected between Age Group and Cap Lamp for 

contrast sensitivity. Additional statistical analysis indicated that 

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 sensitivity 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 our findings 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 potential 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 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 suggest 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 short-wavelength spectral content can 

improve visual performance. Note that the prototype LED cap lamp 

had the most short 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 or allowing quicker 

estimation of the speed and direction with which a machine is moving. 

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. Our research has 

indicated that there are significant differences 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 outputs respectively decreased an additional 35% and 3%. 

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 spectral 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. 

ACKNOWLEDGEMENTS 

The studies described in this paper were conducted with 

assistance from J. Bartels, T. Lutz, A. Mayton, M. Nelson, and J. 

Srednicki, of NIOSH PRL. Vision testing of subjects was conducted by 

M. A. Rossi R.N. 

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