NASA/TM–2009–214784 

Solid State Light Evaluation in the US Lab 

Mockup 

 

James C. Maida 

Space Human Factors Lab – Flight Projects Division 

NASA Johnson Space Center 

Houston, Texas 77058 

Charles Bowen 

Space Human Factors Lab – Flight Projects Division 

NASA Johnson Space Center 

Houston, Texas 77058 

Chuck Wheelwright (retired) 

Space Human Factors Lab – Flight Projects Division 

NASA Johnson Space Center 

Houston, Texas 77058 

March 2009
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NASA/TM–2009–214784 

Solid State Light Evaluation in the US Lab 

Mockup 

 

James C. Maida 

Space Human Factors Lab – Flight Projects Division 

NASA Johnson Space Center 

Houston, Texas 77058 

Charles Bowen 

Space Human Factors Lab – Flight Projects Division 

NASA Johnson Space Center 

Houston, Texas 77058 

Chuck Wheelwright (retired) 

Space Human Factors Lab – Flight Projects Division 

NASA Johnson Space Center 

Houston, Texas 77058 

March 2009
Available from: 

NASA Center for AeroSpace Information National Technical Information Service 

7115 Standard Drive 5285 Port Royal Road 

Hanover, MD 21076-1320 Springfield, VA 22161 

301-621-0390 703-605-6000 

This report is also available in electronic form at http://ston.jsc.nasa.gov/collections/TRS/ 
i 

Contents 

1.0 Background ....................................................................................................................... 1 

2.0 Experimental Conditions Apparatus.................................................................................. 2 

3.0 Experiment Procedure .......................................................................................................7 

4.0 Results .............................................................................................................................. 7 

Appendix A: Response Worksheets ............................................................................................. 15 

Appendix B: Rating Survey Responses........................................................................................ 18 

Appendix C: Contrast Sensitivity and the Perception of SSL Glare ............................................ 19 

Figures

Figure 1. Transverse partition as viewed from SSL side............................................................ 3 

Figure 2. Workstation, GLA side of partition. ........................................................................... 3 

Figure 3. Node 1 end cone surfaces. .......................................................................................... 4

Figure 4. Fluorescent GLA spectra ............................................................................................ 5 

Figure 5. Filtered and unfiltered SSL spectra............................................................................. 5 

Figure 6. Text sample, wire cable, and computer....................................................................... 6 

Figure 7. .................................................................................................................................... 8 

Figure 8. .................................................................................................................................... 8 

Figure 9. .................................................................................................................................... 9 

Figure 10. .................................................................................................................................... 9 

Figure 11. .................................................................................................................................. 10 

Figure 12. .................................................................................................................................. 10 

Figure 13. .................................................................................................................................. 11 

Figure 14. .................................................................................................................................. 11 

Figure 15. .................................................................................................................................. 12 

Figure 16. .................................................................................................................................. 12 

Figure 17. .................................................................................................................................. 13 

Figure 18. .................................................................................................................................. 13 

Figure 19. .................................................................................................................................. 14 

Figure 20. Human contrast sensitivity function ......................................................................... 19 
ii 

Acronyms 

CCT correlated color temperature 

GLAs general luminaire assemblies 

ISS International Space Station 

JSC Johnson Space Center 

LED light-emitting diode 

SSL solid state light 
1 

1.0 Background 

This document constitutes the publication of work performed by the Space Human Factors 

Laboratory (mail code SF5 at the time) at Johnson Space Center (JSC) in the months of June and 

July 2000. Originally, the report was to be a document for internal consumption at JSC as it was 

seen as preliminary work for the development of solid state illumination for general lighting on 

future space vehicles and the International Space Station (ISS). Due to funding constraints, 

immediate follow-on efforts were delayed and the need for publication of this document was 

overcome by other events. However, in recent years and with the development and deployment of 

a solid state light (SSL) luminaire prototype on the ISS, the time was overdue for publishing this 

information for general distribution and reference. 

SSLs are being developed to potentially replace the general luminaire assemblies (GLAs) 

currently in service in the ISS and included in designs of modules for the ISS. The SSLs consist 

of arrays of light emitting diodes (LEDs), small solid state electronic devices that produce visible 

light in proportion to the electrical current flowing through them. Recent progressive advances in 

electrical power-to-light conversion efficiency in LED technology have allowed the consideration 

of LEDs as replacements for incandescent and fluorescent light sources in many circumstances, 

and their inherent advantages in ruggedness, reliability, and life expectancy make them attractive 

for applications in spacecraft. One potential area of application for the SSLs is in the US 

Laboratory Module of the ISS. This study addresses the suitability of the SSLs as replacements 

for the GLAs in this application. 

Three human factors questions were addressed by the study. First was whether the illumination 

level provided by the mockup GLAs was adequate for the performance of the visual tasks and 

whether there was any difference in performance under illumination from SSLs adjusted to a 

comparable level. The second question addressed the importance of the spectral characteristics of 

the illumination for the visual tasks being studied. The third question involved whether the 

astronauts sensed any differences in the way they perceived the US Laboratory Module 

environment with GLA or SSL lighting. 
2 

2.0 Experimental Conditions and Apparatus 

The evaluation was designed to take a “quick look,” from the human factors standpoint, at the 

suitability of SSLs as replacements for the GLAs in the US Laboratory Module working 

environment. Three visual tasks for the evaluation were selected to broadly represent some of those 

likely to be encountered in this environment: (1) reading printed text and equipment legends; (2) 

interacting with computers; and (3) comparing/judging colors. Special attention was paid to 

controlling the light levels and spectral characteristics during the performance of the visual tasks. 

Participants were drawn from the pool of astronauts training for ISS missions at JSC. 

The environment for the experiment was the US Laboratory Module mockup of the Space Station 

Mockup Test Facility. Standard lighting for the module is provided by 12 GLAs. For the 

experiment, six Sylvania mockup GLAs were installed. A removable temporary Foamcore partition 

was installed transversely at the midpoint of the module (figure 1), and the six GLAs above Bay 04 

through Bay 06 were replaced with SSLs. This allowed two sets of isolated lighting conditions to be 

produced simultaneously in the two halves of the module. An access door was constructed in the 

partition to allow the experiment conductor and participant rapid access to both sides of the 

partition. Removable work surfaces were fitted to the starboard rack of Bay 02 on the GLA side of 

the partition (figure 2) and to the port rack of Bay 05 on the SSL side (figure 1). The vertical rack 

surface above and behind the work surface on the GLA side (figure 2) was covered with Foamcore 

material to approximate the reflective characteristics of the rack panels adjacent to the work surface 

on the SSL side. The blue end cone surfaces at the Node 1 end of the Lab Module were also 

covered with Foamcore (figure 3) to more nearly match the reflective characteristics of the Node 

2 end cone. 
3 

Figure 1. Transverse partition as viewed from SSL side. 

Figure 2. Workstation, GLA side of partition. 
4 

During the experiment, all individual dimmer controls on the GLAs were adjusted for maximum 

brightness, and the illumination from the SSLs was adjusted to produce equivalent illuminance 

readings (22 to 23 foot-candles [fc]) in the centers of the work surfaces on both sides of the 

partition. Illuminance readings on equipment rack surfaces throughout the module exceeded the 

work surface values by as much as 10 fc near the “tops” of the racks beneath the luminaires, 

while readings on the rack surfaces near the floor were as low as 5.6 fc. Ganged control of 

illumination from the SSLs was effected by adjusting the common direct current voltage applied 

to the SSL luminaires. Time for SSL thermal stabilization was allowed following adjustments in 

power supply settings to minimize variations in SSL illumination. Electrical current drawn by the 

SSLs and work surface light levels were monitored throughout the experiment sessions. 

A set of filters were constructed for use with the SSLs in the second session of the experiment. 

These were designed to adjust the correlated color temperature (CCT) of the SSLs to approximate 

the CCT of the GLAs. The CCT of the Sylvania GLAs was measured to be 4324°K, whereas the 

CCT of the SSLs was measured to be 6700°K and 4166°K for the unfiltered and filtered cases, 

respectively. The filter material used was Rosco International Type 3442, a commercial stabilized 

gelatin stage lighting filter film. Color characteristics of the lights used in the experiment were 

measured with a Photo Research Model 650 colorimeter. Visible spectra for the lights are shown 

in figures 4 and 5. 
5 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

380 420 460 500 540 580 620 660 700 740 780

W avelength (nm)

Radiance (W /m2/sr)

Figure 4. Fluorescent GLA spectra.

Figure 5. Filtered and unfiltered SSL spectra. 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

380 420 460 500 540 580 620 660 700 740 780

W avelength (nm)

Radiance (W /m2/sr)

Unfiltered

Filtered
6 

Text samples were prepared for the participants to read under the various experimental lighting 

conditions. These were drawn from current short summaries of technical papers on various topics 

published in Science News. Each article was transcribed and printed on white paper in 10-point sans 

serif (Arial) font. Transcribed text was single spaced, providing a greater challenge to the reader. 

The laptop computer used in the experiment was a Fujitsu Lifebook Model L470 (figure 6), 

having a 9-inch diagonal back-lighted LCD color display. The settings for the display brightness 

and contrast were fixed during the experiment to produce approximately 16.5fL, 11.0fL, 6.7fL 

brightness readings for the respective white, gray, and black areas of the survey display. All 

survey prompts were displayed and responses and comments were recorded by means of the 

computer. Software supporting these activities consisted of a group of Microsoft Excel 

spreadsheets including option buttons for survey responses and text boxes for comment entries. 

Spreadsheet contents are represented in their initialized state in Appendix A. Once a selection 

was made from a group of buttons, it remained active until the end of the session or an alternate 

button was selected. 

Challenges to color rendering under the experimental lighting conditions were explored by having 

the participants examine a cable with multicolored insulated 22 American Wire Gauge wires to 

judge the ease of identifying (naming) colors and the ease of differentiating between the colors. 

Figure 6. Text sample, wire cable, and computer. 
7 

3.0 Experiment Procedure 

The participants performed the experiment in two sessions. In each session, responses to one of 

the forms of the SSL were examined along with the responses to the GLAs. The SSLs used in the 

first session were unfiltered, and the second session used the same SSLs fitted with filters to alter 

the light spectrum to approximate the CCT of the GLAs. This arrangement precluded complete 

balancing of the order of presentation of the different lighting conditions, but it eliminated the 

considerable time required to install or remove the filters, thereby reducing the time required of 

the participants to complete the experiment. Within each session, however, the order of 

presentation of the GLA or SSL conditions was randomly balanced, with half the participants 

experiencing each order. 

The same sequence of tasks was used for both lighting conditions in each session. First, the 

participant was provided with a printed page of black-on-white printed text. After reading the 

passage, the participant completed the rating survey on the computer. A second rating survey 

relating to the ease of computer use in the lighting environment followed the text reading. Once 

the reading and computer use surveys were completed, the participant was provided with an 

electrical cable comprised of wires with multicolored insulation. The participant examined the 

colored wires and again turned to the computer to complete the last portion of the rating survey, 

which related to the ease of color judgment and the overall module lighting characteristics. 

4.0 Results 

The use of an Excel spreadsheet for collecting the ratings allowed relative ease in categorizing, 

counting, and graphically representing the response frequencies. A tabulation of responses to the 

rating survey items is included as Appendix B. 

The survey responses and comments were interpreted to indicate the following results: 

• The SSL is a suitable replacement for the GLA. 

• The CCT of the evaluated SSLs is acceptable for the tasks performed. 

• Glare in the US Laboratory Module is not significant with either GLA or SSL 

lighting. 

• The availability of higher light intensity than that provided by the current GLA 

would be beneficial. 

• SSL fixtures should be made available for long-term evaluations and routine 

mockup training activities. 

Responses to survey items are summarized in figures 7 through 19. In these charts, the response 

categories “strongly agree” and “somewhat agree” are combined as “agree.” Similarly, the 

“strongly disagree” and “somewhat disagree” categories are lumped together as “disagree.” 
8 

Figure 7

Figure 8 

The color of the lighting distracts me while reading 

black-on-white text.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree

The module lighting is bright enough to read blackon-white text comfortably.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree
9 

Figure 9 

Figure 10 

The module lighting seems harsh or glaring when I 

am reading black-on-white text.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree

The distribution of light within the module is 

satisfactory for reading black-on-white text.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree
10 

Figure 11 

Figure 12 

The module lighting is bright enough to allow me to 

use the computer comfortably.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree

The color of the lighting distracts me while I am 

using the computer.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree
11 

Figure 13 

Figure 14 

The module lighting seems harsh or glaring when I 

am using the computer.

0

2

4

6

8

10

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree

The distribution of light within the module is 

satisfactory for using the computer.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree
12 

Figure 15 

Figure 16 

The lighting makes it difficult to distinguish some 

wire colors from others.

0

2

4

6

8

10

12

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree

The lighting makes it difficult to identify the colors 

of some of the wires.

0

2

4

6

8

10

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree
13 

Figure 17 

Figure 18 

The overall illumination allows easy reading of 

labels on equipment throughout the module.

0

1

2

3

4

5

6

7

8

9

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree

The distribution of light within the module is 

satisfactory.

0

2

4

6

8

10

GLA SSL Filtered SSL

Response Count

Agree

Ambivalent

Disagree
14 

Figure 19 

The color of the lighting makes the module seem 

warm/cold.

0

1

2

3

4

5

6

7

8

9

GLA SSL Filtered SSL

Response Count

Warm

Ambivalent

Cold
15 

Appendix A. Response Worksheets 

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

T he m odule lighting seem s harsh or glaring w hen I am reading black-on-w hite text.

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

T he lighting conditions for reading black-on-w hite text are uniform throughout the module.

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

T he module lighting is bright enough to read black-on-w hite text comfortably.

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

T he color of the lighting distracts m e w hile I am reading black-on-w hite text.

Comments regarding reading black-on-white text:

Please read the printed article and then answer the following questions:
16 

T he module lighting is bright enough to allow me to use the computer comfortably.

T he color of the lighting distracts m e w hile I am using the com puter.

T he m odule lighting seem s harsh or glaring w hen I am using the com puter.

T he lighting conditions for computer use are uniform throughout the module.

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

Comments regarding computer use:
17 

T he overall illumination allow s easy reading of labels on equipment throughout the module.

T he difference in brightness betw een lighter and darker areas in the module is satisfactory.

T he color of the lighting makes it difficult to distinguish wire colors.

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

Completely agree

Somewhat agree

Neither agree nor disagree

Somewhat disagree

Completely disagree

T he color of the lighting makes the module seem:

Warm

Somewhat warm

Neither warm nor cold

Somewhat cold

Cold

Comments:

Please perform the wire matching task and then answer the following questions:
18 

Appendix B: Rating Survey Responses 

 Response Frequencies

Light Question Comp. S’what S’what Comp. No 

Type Category Question agree agree Ambiv. disagree disagree Resp. 

 Bright enough? 5 2 1 3 1 0 

Text Color distracting? 0 1 3 1 7 0 

Reading Harsh or glaring? 0 0 2 2 8 0 

 Brightness ratio OK? 4 3 1 3 0 1 

 Bright enough? 8 2 0 1 0 1 

Computer Color distracting? 0 1 2 2 6 1 

GLA Use Harsh or glaring? 0 2 2 3 4 1 

 Brightness ratio OK? 5 4 1 1 0 1 

 Color distinguishing problem? 2 2 0 3 5 0 

Color Color naming problem? 2 2 0 3 4 1 

& Easy to read labels? 5 3 0 4 0 0 

Overall Brightness ratio OK? 4 3 0 4 1 0 

 Warm (agree)/cold? 1 2 5 3 1 0 

 Bright enough? 6 3 1 0 1 1 

Text Color distracting? 0 1 1 2 8 0 

Reading Harsh or glaring? 1 3 2 1 5 0 

 Brightness ratio OK? 7 2 0 2 0 1 

 Bright enough? 7 3 0 0 0 2 

Computer Color distracting? 0 1 0 3 7 1 

SSL Use Harsh or glaring? 0 4 1 1 5 1 

 Brightness ratio OK? 6 3 2 0 0 1 

 Color distinguishing problem? 0 1 1 2 5 3 

Color Color naming problem? 0 4 0 1 6 1 

& Easy to read labels? 4 4 0 4 0 0 

Overall Brightness ratio OK? 4 4 2 2 0 0 

 Warm (agree)/cold? 2 1 5 3 1 0 

 Bright enough? 6 4 0 1 1 0 

Text Color distracting? 1 0 2 3 6 0 

Reading Harsh or glaring? 0 1 2 4 5 0 

 Brightness ratio OK? 5 6 0 1 0 0 

SSL Bright enough? 8 1 1 0 0 2 

with Computer Color distracting? 0 2 1 3 5 1 

Filter Use Harsh or glaring? 0 1 0 6 3 2 

 Brightness ratio OK? 5 5 0 0 1 1 

 Color distinguishing problem? 5 5 0 0 1 0 

Color Color naming problem? 0 3 0 2 7 0 

& Easy to read labels? 0 3 2 1 6 0 

Overall Brightness ratio OK? 4 5 1 2 0 0 

 Warm (agree)/cold? 3 5 1 3 0 0 
19 

Appendix C. Contrast Sensitivity and the Perception of SSL Glare 

Glare is predicted when a light source or reflective surface in the observer’s field of view exceeds 

the surrounding brightness by a ratio of 12:1 or more. An additional factor not usually considered 

in predicting glare is the human contrast sensitivity function. This characteristic, shown in figure 

20, relates the sensitivity of the human visual system to periodic spatial variations in contrast 

(brightness). The graph of figure 20 shows that humans respond most strongly to variations in 

contrast in the spatial frequency range from about two to four cycles per degree of visual angle. 

When considered from the standpoint of contrast sensitivity, the periodic spacing of rows of 

LEDs arrayed in an SSL may conspire with the interior dimensions of a habitable structure such 

as the US Laboratory Module to exacerbate the perception of glare from the luminaire. The visual 

angle, α , between two points S distance apart from one another and viewed from a distance D is 

calculated as ( ) 1 α 2 tan 2 S D − = . For example, assuming that the spacing between rows of 

LEDs in the SSL is 0.3 inch (similar to the row spacing in the SSLs used in this experiment), and 

that viewing distances range from 2 feet to 7 feet, the row spacing in terms of visual angle 

occupies from 0.205o to 0.716o. Since the fundamental spatial frequency corresponding to the 

LED spacing, sf , is the reciprocal of the visual angle α , the range of fundamental spatial 

frequencies corresponding to this range for α in cycles per degree (~/°) is 

{1.4~/ 4.9~/ °≤ ≤ ° fs } . The range for sf in this example thus brackets the peak of the contrast 

sensitivity function, possibly increasing the likelihood of the perception of glare. The spacing of 

point source illumination elements in arrays to form luminaires might well be considered in 

relation to the dimensions of the space in which they may be viewed when designing for 

increased visual comfort. 

Figure 20. Human contrast sensitivity function. 

Reference: Owsley, Cynthia, Robert Sekuler, and Dennis Siemsen (1983). Contrast sensitivity 

throughout adulthood. Vision Research 23(7), 689-699. 

10

100

1000

0.1 1 10 100

Spatial Frequency (cycles/degree)

Contrast Sensitivity

Age 20-30

Age 60-70
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 March 2009 NASA Technical Memorandum 

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Solid State Light Evaluation in the US Lab Mockup 

6. AUTHOR(S) 

James C. Maida, Charles Bowen, Chuck Wheelwright 

NASA Johnson Space Center, Houston, TX 77058 

 

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TM–2009–214784 

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13. ABSTRACT (Maximum 200 words)

Solid state lights (SSLs) are being developed to potentially replace the general luminaire assemblies (GLAs) currently in service in 

the ISS and included in designs of modules for the ISS. The SSLs consist of arrays of light emitting diodes (LEDs), small solid state 

electronic devices that produce visible light in proportion to the electrical current flowing through them. Recent progressive advances 

in electrical power-to-light conversion efficiency in LED technology have allowed the consideration of LEDs as replacements for

incandescent and fluorescent light sources in many circumstances, and their inherent advantages in ruggedness, reliability, and life 

expectancy make them attractive for applications in spacecraft. One potential area of application for the SSLs is in the US Laboratory 

Module of the ISS. This study addresses the suitability of the SSLs as replacements for the GLAs in this application. 

14. SUBJECT TERMS 15. NUMBER OF 

PAGES 

16. PRICE CODE 

light sources, lighting equipment, aircraft lights, illuminating, US Laboratory Module 28 

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