Helmet-Mounted Displays: - USAARL - The - U.S. Army

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Clarence E. Rash and William E. McLean
some applications, and that, through the use of limited color displays, the
cost and complexity of color HMDs may be reduced while maintaining the
advantages of color. Reinhart and Post (1996) conducted a study looking
at the merits and human factors of two-primary color AMLCDs in helmet
sighting systems. One of their conclusions was that such a design could
prove beneficial in an aviation HMD application.
Besides cost, weight, and complexity drawbacks to the implementation
of color HMDs, additional issues are present. The luminous efficiency of
the eye is a function of wavelength and adaptation state. For example, at
photopic levels of illumination, the eye is most efficient at 555 nm,
requiring at other wavelengths more energy to perceive the same
brightness. Therefore, care must be taken in multiple color display designs
to ensure isoluminance (Laycock and Chorley, 1980). Also, it has been
found that larger size symbols are required to ensure that both detail and
color can be perceived when color is selected over black and white
(DeMars, 1975).
One final issue for this section is the chromatic aftereffects reported
with I 2 devices. This problem first was raised in the early 1970s (Glick and
Moser, 1974). This afterimage phenomenon was reported by U.S. Army
aviators using NVG for night flights. It was initially, and incorrectly,
called “brown eye syndrome.” The reported visual problem was that
aviators experienced only brown and white color vision for a few minutes
following NVG flight. Glick and Moser (1974) investigated this report and
concluded that the aviator’s eyes were adapting to the monochromatic
green output of the NVGs. When such adaptation occurs, two phenomena
may be experienced. The first is a “positive” afterimage seen when looking
at a dark background; this afterimage will be the same color as the adapting
color. The second is a “negative” afterimage seen when a lighter
background is viewed. In this case, the afterimage will take on the
compliment color, which is brown for the NVG green. The final
conclusion was that this phenomenon was a normal physiological response
and was not a concern. A later investigation (Moffitt, Rogers, and
Cicinelli, 1988) looked at the possible confounding which might occur
when aviators must view color cockpit displays intermittently during
prolonged NVG use. Their findings suggested degraded identification of
green and white colors on such displays, requiring increased luminance
levels.
References