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The photographs in figures 7 and 8 offer dramatic evidence of the windshield reflectances shown in Table III in the columns labeled dash reflection. Figure 7 shows a man standing on a tree-covered street. The photograph was taken with black velveteen lying on the dash top. Figure 8 shows the same scene without the velveteen light absorber. As a pedestrian in broad daylight, he wouldn't suspect that he was invisible to the driver.

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Recommendations:

To achieve optimum visual performance at distance the automobile driver must be provided a daytime highway scene with the controllable items in the field of view adjusted to hold brightness levels equal to or lower than the average scene brightness but not lower than 1/10. Since the average scene was measured in this study to be 11.7% of the outside natural illumination, all objects receiving direct sunlight, e.g., the hood, the steering wheel, wiper blades, etc., should reflect not more than 10%. Corner posts and automotive interiors not receiving direct illumination should be of high reflectance values to keep away from excessively dark objects anywhere in the field of view. The surfaces reflecting in the windshield, however, must be as black and dull as possible to control veiling glare.

So that the driver may achieve optimum visual performance in reading the instruments of the dash panel, the instruments should be equal to or brighter than the immediate surrounding panel by an amount of up to 3 to 1 but not brighter than 10 to 1. Furthermore, to make it possible to adapt quickly from far seeing to dash panel seeing, illumination on the dash panel must be improved. A value to strive for is not less than 1/3 of the average outdoor scene brightness. Summary and Conclusions:

A. This study on windshield and instrument panel characteristics has shown:

1. All of the fifty-six 1959-62 automobiles tested had serious faults so far as the visibility of the highway and the instrument panel in the daytime is concemed.

2. The amount of light reflected from the top of the dash onto the windshield and into the eyes of the driver averages over 15% of the average scene luminance.

3. The amount of light scattering dirt on automobile windshields is small, and variable as one would expect, averaging only 4.8%. 4. Glare sources of exceedingly high intensities were noted and all cars tested had chromium trim of various types in the field of the view of the driver.

5. Dash panel instrument illumination was generally much too low in the daytime to permit the meters to be seen at a glance. This is in addition to the problem in 4 above which further interferes with quick seeing.

B. Every vision engineering defect noted in this study can be remedied by the automobile manufacturers by practical and economical changes. Specific recommendations are made in the text.

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1) Allen, Merrill J., Certain Visual Aspects of the Modern Automobile, Journal of the American Optometric Association, December 1962.

2) Allen, Merrill J., A Study of Visual Performance Using Opthalmic Filters. ASD Technical Report 61-576, pp. 21-26, October 1961, United States Air Force, Wright-Patterson Air Force Base, Ohio.

3) Borish, Irvin M., Clinical Refraction, Chicago, The Professional Press, 1949, Pg. 110.

4) Duke Elder, Sir W. Stewart, Textbook of Ophthalmology, Mosby Co., Vol. IV, 1950, Pg. 4492

5) I.E.S. Handbook, 3rd Edition, Illuminating Engineering Society, 1860 Broadway, New York, New York, 1959. Sect. 12, Pg. 6; also see Sect. 2, Sect. 14, Pg. 3, Sect. 15, Pg. 3.

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FIGURE I SOURCES OF VEILING GLARE IN AN AUTOMOBILE WINDSHIELD

97767 0-63- -10

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Abbreviations: Dir. Direction; T.- Top; B.- Bottom; P.- Panel.

Gradient

Charcoal

S

4:25 Cloudy

Gradient Gradient Clear

Charcoal

S

4:00 Clear

Dark Brown

N-NE

2:50 Clear

Clear

Cream Grey

NE

1:30 Clear

N

11:50 Clear

Clear

Fire Eng. Red
Med.-Drk. Beige NE
Med.-Drk. Brown N W

W-NW

1:30 Cloudy

12:00 Cloudy

4:10 Lt. Haze

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