Iv.

a function of increasing aperture size, the data for the
three aperture sizes have been combined to yield an overall
recognition value for each light at three intensity values
as viewed through the three panels. Both sunscreen panels
yielded overall lower recognition values than did the clear
panel with the greatest differences between the panels
tending to occur at the lower and intermediate brightness
levels. Because of the differences in brightness levels of
the three signal colors, their relative effectiveness cannot
be established within the conditions of this study.

Discussion.

The addition of reflective sunscreen materials to window
areas is known to reduce solar heat and brightness within
vehicles, buildings, etc. However, we believe these benefits
must be considered with respect to demonstrated losses in
visual performance that occurred under dim luminance levels.
For example, under a moderate brightness level (5.0 fL),
recognition visual acuity through the clear, silver, and
bronze panels was 20/20, 20/24, and 20/29, respectively.
Comparable acuities scored under dim lighting (1.0 fL) were
20/22, 20/35, and 20/42.

Scores on a task designed to evaluate the subjects'
ability to identify the contour of test targets (square or
diamond) indicated that performance decreased for both
sunscreen materials with marked decreases for low contrasting
targets. Performance also decreased under reduced illumi-
nation and was generally lower for gray targets on a dark-
gray background than for gray targets against a light-gray
background.

Detection of signal light colors in the transportation
environment is considered essential for purposes of navigation,
communication, and collision avoidance. Color identification
scores generally decreased while viewing through either
sunscreen material with decreases particularly evident for
the green and red signal lights presented at the intermediate
and low intensity levels.

In addition, performance scores on each task were generally
highest for nontreated glass and lowest for the bronze
sunscreen material. These results follow the spectral light
transmission curves for the clear, silver, and bronze panels
shown previously.

12


presentation, Subjects who failed to identify all 20/40
figures were arbitrarily given a score of 20/50 for the
purpose of computation,

The second test consisted of four display cards pre-
sented at all luminance ratios, Each card measured 30 cm
(12 in) on a side and was divided into four equal squares,
Two squares on each card were constructed from dark-gray
paper (Pantone No. 432) and two from light-gray paper (Pantone
No. 428). Centered within each square was a single square
or diamond test figure subtending a visual angle of 10 arc
min; i.e., 17.5 mm measured diagonally and 12.35 mm on each
side, To obtain various figure-to-ground contrast ratios,
test figures displayed on dark-gray backgrounds were lighter
shades of gray (Pantone Nos, 422, 428, 430, and 431). Test
figures displayed on light-gray squares were dark shades
of gray (Pantone Nos. 422, 430, 431, and 432), Luminance
values used to calculate figure-to-ground contrast ratios
are specified as the brightness difference between target
and background divided by the background brightness.

During the evaluation, two test figures (one diamond and
one square) representing each contrast ratio were presented
for all sunscreen panel and brightness combinations. Sub-
jects were instructed to respond to the test figures only
when they were distinguishable.

The third test using the modified Edridge-Green Lantern
was conducted at one external/internal luminance ratio
(5:1). While viewing through each sunscreen or the clear
panel, subjects attempted to identify a red, green, or
white light presented for 3.0 seconds. Lights were dis-
played in random order in combinations of each of three
intensity levels and three aperture sizes. Intensity
levels were controlled by three neutral density filters in
the body of the lantern and were measured with the Pritchard
Spectra photometer, The circular apertures were 1.0, 1.4,
and 1.7 mm (0.040, 0.055, and 0.067 in), respectively, in
diameter and are equivalent in angular size to a 16-cm
(5.5-in) signal light at 838, 610, and 500 m (917, 667, and
547 yd), respectively. A Gamma Spectroradiometer, Model
2900MR, was used to determine light energy distribution
curves for each of the three signal light colors used in
the study (Figure 1). All values are based on the Edridge-
Green Lantern after modification for 120V operation with a
G.E. 75W soft-white bulb. Shown in Figures 2-4 are the

3



IIl.

relative spectral energy for each signal light source and
panel combination. Relative spectral energy curves were
obtained without a photopic correction filter positioned
before the photomultiplier tube.

Light transmission values through each sunscreen and
clear panel were also obtained with a Pritchard Spectra
photometer and a standard white luminance source (Spectra
100 fL). Transmission values through the clear, gold,
silver, and bronze panels were 92, 20, 18, and 8 percent,
respectively. Light transmission was reduced by 2 percent
when measurements were made with panels positioned 45° to
the measurement axis,

Results,

Figure 5 shows the visual acuity levels attained when
viewing through the three panels under the five combinations
of interior and target luminance levels, There is little
or no impairment of visual acuity at any of the luminance
ratios when viewing through the clear (control) panel.

Both sunscreen panels are shown to be detrimental to visual
acuity except at the 50-fL target luminance level.

Figure 6 shows the percentage of correct responses on
the contrast discrimination task for three of the five
luminance ratios. Performance was uniformly high (at or
near 100 percent) with all three panels when the target
luminance was 50 fL. At the lower target luminance values,
contrast discrimination was uniformly high when viewing
through the clear panel but was generally poorer when view-
ing through the sunscreen panels, especially for those
targets having a relatively low figure-to-ground contrast
ratio. If the negative contrast ratios (light or dark
background) are converted to equivalent positive values,
the two sets of contrast values are approximately equal.
However, data indi¢ate that targets with a positive figure-
to-ground contrast ratio are discriminated better than those
with a negative contrast ratio when viewed through the
sunscreen panels,

Figure 7 gives the results for the signal light
recognition task for each of the three signal light colors.
Although there was a general improvement in performance as


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Technical Report Documentation Page

2. Government Accession No. 3. Recipient's Catalog No.

1. Report No.

FAA-AM-7 8-28

‘4. Title and Subtitle

VISUAL PERFORMANCE ASSESSMENT THROUGH CLEAR AND
SUNSCREEN-TREATED WINDOWS

5. Report Date

6 Performing Organization Code

@

[8. Performing Organization Report No.

7. Author's) Kenneth W. Welsh, Paul G. Rasmussen, and

John A. Vaughan

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)
FAA Civil Aeromedical Institute.

P.O. Box 25082 TT. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name ond Address,
Office of Aviation Medicine
Federal Aviation Administration
800 Independence Avenue, S.W.
Washington, D.C. 20591

14. Sponsoring Agency Code

15. Supplementary Notes

Work was performed under Task AM-D-78-PHY-111.

16. Abstract
Reflective sunscreen filters are frequently bonded to vehicle windows to reduce
interior heat and brightness. The present study was conducted to investigate the
optical properties of and visual performance through clear and sunscreen-treated
glass panels that served as windows in an observation booth. Five combinations of
external and internal brightness levels were used.

Light transmission values through the clear, gold, silver, and bronze panels were
92, 20, 18, and 8 percent, respectively. Visual performance tests were conducted
at 6 m (20 ft) on 12 subjects with normal visual acuity and color vision.

Two tasks were conducted under brightness levels on the external display and in
the subject's booth, respectively, of 1:1, 5:1, 50:1, 5:5, and 50:5 fL. Visual
acuity using Landolt C figures and scores on a contour identification task were
minimally impaired for any luminance ratio when the clear (control) panel was used.
With the sunscreen panels, scores on both tests decreased as a function of target
brightness and panel density.

With one external/internal luminance ratio (5:1), identification of signal light
colors was generally impaired while viewing through sunscreen materials. Decreases’
were particularly evident for green and red lights presented at intermediate and
low intensity levels.

17, Key Words 18, Distribution Statement

Document is available to the public through
the National Technical Information Service,
Springfield, Virginia 22161.

Visual Performance
Sunscreens
Aviation Safety

19. Security Classif. (of this report)

Unclassified

20. Security Classif, (of this page)

Unclassified

21. No. of Pages

14

22. Price

Form DOT F 1700.7 (8-72)

Reproduction of completed page authorized



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LUMINANCE RATIOS (Exterior : Interior)

FIGURE 5. Visual acuity of Landolt C figures with clear,
silver, and bronze panels under selected
luminance levels.



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names of Solar Master PSL-80 bronze, PSL-80 gold, and M-80
silver, These materials were laminated to 6.35-mm (0,25-in)
polished plate glass with outside dimensions of 46 by 61 cm
(18 by 24 in). One clear glass panel was ordered without
sunscreen material and used to obtain control data. Gold
and silver panels were found to have similar spectral trans-—
mission characteristics and preliminary tests indicated
equal performance levels through both panels, Visual per-
formance data will therefore be presented for two sunscreen
panels (bronze and silver) and for the clear noncoated
plate glass,

Subjects viewed the test displays from a distance of
6 m (20 ft) while seated in an observation booth, The sub-
jects' heads were supported by a chin rest while they looked
perpendicularly through the central portion of the viewing
window.

Visual performance was evaluated under selected luminance
levels that were controlled separately for the display area
and the observation booth. The display area was illuminated
by three daylight-blue bulbs (G.E., 100W) positioned in a
triangular array and directed toward the target. Luminance
levels were adjusted by a variable power source to provide
1.0, 5.0, and 50.0 fL on the display. Brightness levels
in the observation booth were obtained by directing light
from a single daylight-blue bulb through the diffusing side
widow of the booth. The center of the window was located
approximately 30.5 cm (12 in) above the subject's line of
sight. Luminance levels in the enclosure were adjusted to
1.0 and 5.0 £L as measured from a standard reflectance
plaque held against the inside surface of the viewing window
while the photometer was located at a position approximating
the location of the subject's head. Data were obtained
with brightness level ratios on the display and in the booth
respectively of 1:1, 5:1, 50:1, 5:5, and 50:5 fL.

Two visual performance tasks were conducted under each
of the five luminance ratios noted above, The first test
device consisted of 12 Landolt C figures with three figures
for each of four acuity levels (20/40, 20/30, 20/25, and
20/20). Subjects were asked to identify the location of
the gap of each Landolt C figure (up, down, left, or right).
The display was presented twice at each external/internal
brightness ratio with figures positioned after each

2


Although not evaluated in depth, performance appears to
decrease as the internal brightness level approaches the
external ambient brightness. Degradation of vision would
presumably be greatest under moderately dim external illumi-
nation levels such as dusk and nighttime flying or driving.
When internal brightness exceeds external levels, mirrorlike
reflections from the inside viewer's side of the sunscreen-
treated window could markedly reduce visual perception of the
exterior environment. Under nighttime conditions, further
losses would also be expected from reflections of instrument
panel lights from the side windows of the airplane.

Visual performance could be reduced even further by the
wearing of sunglasses while viewing through sunscreen
materials. Studies cited in a text by Allen (1) and articles
by Blackwell (2,3) indicate that recognition and response
time to nonluminous targets may be reduced with sunglasses
or tinted windshields under moderately dim ambient illumination.

13



II.

VISUAL PERFORMANCE ASSESSMENT THROUGH CLEAR
AND SUNSCREEN-TREATED WINDOWS

Introduction.

Metallic-coated sunscreen materials are frequently
bonded to windows of cars, trucks, and other vehicles. These
reflective materials are recommended by their manufacturers
to reduce the buildup of interior heat and reduce ambient
brightness within such vehicles. Sunscreen materials have
also been used in airplanes, as evidenced by an FAA Aircraft
Services Base (ASB) test (ASB Project No. 350088) conducted
in 1976-77 to evaluate reduction of the "greenhouse effect"
in the cockpit. During the test, heat-reflective Mylar film
was laminated to the rear side windows and overhead "eyebrow"
windows of the cockpit of a Sabreliner 80 airplane.

The present study was conducted because of reports of
visual degradation through the sunscreen-treated cockpit
windows during day- and night-flying conditions. The reports
included complaints of reduced visibility of the air-
port environment during circling approaches, difficulty in
tracking airplanes from nontreated to treated window panels,
and daytime reflections of the cockpit radio instruments
from the sunscreen-treated eyebrow windows.

Our results from a laboratory study conducted with three
sunscreen materials include spectroradiometric values and
scores from several performance tasks conducted under
selected illumination conditions.

Methods.

Subjects consisted of 10 volunteer males and 2 females
with ages ranging from 24 to 64 years (mean 47 years). All
subjects had 20/20 distant visual acuity; nine subjects
required spectacle correction to achieve optimum vision.

In addition, each subject was evaluated with the Farnsworth
Lantern (red, green, and white lights) and was determined
to have normal color perception under standard testing
conditions.

The three sunscreen films used in the study were manu-
factured by DuPont Corporation and distributed under the





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1.

2.

REFERENCES

Allen, M. J.: Vision and Highway Safety, Philadelphia,
Chilton Book Company, pp. 35 and 112, 1970.

Blackwell, H. R.: The Effect of Tinted Optical Media Upon
Visual Efficiency at Low Luminance, J. OPT. SOC. AMER.,
43:815, 1953.

Blackwell, H. R.: Visual Detection at Low Luminance Through
Optical Filters, Highway Research Board Bulletin 89, p. 43,
1954,

14