Contrast sensitivity and visual acuity data are used to derive a unified visual performance
contour which describes the generalized improvement in visual performance resulting as task
background luminance is increased. Factors which influence the difficulty of visual tasks are
described, and examples are given of the degree of task background luminance, and hence illuminance,
required to permit criterion levels of performance for sample tasks. Physical principles and devices
are described which permit measurements of: (a) task object contrast, (b) the integral of ocular
light scatter which reduces task image contrast, and (c) the joint effect of luminance differences
in the environment which produce transitional adaptive effects on visual performance. These physical
aspects of luminous environments are shown to influence visual performance in quantitative ways
which may be assessed by reference to the standard performance contour. An over-all lighting
performance index is derived which takes account of the task background luminance and these three
other measures of the effects physical aspects of luminous environments have upon visual
performance. Lighting performance indices are presented for five sample lighting installations,
which reveal the overriding importance of other aspects of luminous environments than the level of
illuminance they provide. The problem of predicting the over-all visual performance to be expected
from specific luminous environments in advance of construction is discussed, and empirically derived
calculational methods are described.
Loyd A. Jones and George C. Higgins J. Opt. Soc. Am. 37(4) 217-263 (1947)
References
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