UFC 3 -520-01
June 10, 2002
F-4.4.1.1 Disability glare is caused by light sources that obscure visual tasks or make
them hard to see. The reflection of a bright light or window in a computer screen is a
type of disability glare. Similarly, a bare lamp adjacent to a task can make it harder,
rather than easier to see. Disability glare might not be associated with a sense of
discomfort. Because disability glare affects visual performance, attention to potential
problems should be considered essential.
F-4.4.1.2 Discomfort glare occurs when a bright light source makes viewing
uncomfortable, even when a task is not being performed. Natural daylight, if not
properly controlled, can be a co mmon source of discomfort glare. Other sources
include many types of common electric lights. While not as critical for visual
performance, discomfort glare is a cause of eye fatigue and affects long -term worker
productivity.
F-4.4.2 Glare control usually involves source shielding from important viewing angles.
For this reason, many luminaires employ shielding methods such as lenses, louvers or
baffles which obscure the light source from direct view up to about 45 degrees. This
permits light to be focus ed by the luminaire to the visual task below it, but shields a
heads-up view from direct viewing of the light source.
F-5
HUMAN FACTORS.
F-5.1
Adaptation.
F-5.1.1 The process of the eye's adjustment is called adaptation. The eye can adjust
fairly rapidly over a 100:1 range mostly through the dilation or contraction of the pupil.
But the wider the range, the longer the adjustment period. It can take 5 minutes to fully
adapt to starlight (0.01 footcandle) when coming from a room lighted to only 10
footcandles, an adjustment range of 1,000:1. The widest adjustment range for the eye,
from 10,000 footcandles (full noon sun) to starlight (1,000,000:1) can take over an hour.
Adaptation also takes longer with age.
F-5.1.2 Because military operations can involve rapid deployment of personnel into
night and low light level activities, consideration for rapid adaptation might be
necessary. Usually, this involves reduction of light levels in interior spaces and the use
of light sources of appropriate spectrum a nd shielding. Because this is specialized
technology, professional design assistance should be used.
F-5.2
Computer Vision Syndrome (CVS).
F-5.2.1 CVS involves both performance and comfort problems concerning work
involving computer screens, especially cathode ray tube (CRT) screens. Lighting
problems associated with CVS are usually caused by forms of disability and discomfort
glare, too much or too little illumination, and flicker. Because of the importance of
computers in most operations, design lighting systems for spaces involving computer
work to comply with the recommendations of the IESNA contained in IESNA/ANSI
RP-1-93, Office Lighting, as it relates to computer work area illumination.
F-7
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