threshold increment (TI)

[] A measure of disability glare expressed as the percentage increase in contrast required between an object and its background for the object  to be seen equally well with a […]


[] (See luminance contrast.)


[5.12]  [See central (foveal) vision; mesopic vision; peripheral vision; photopic vision; and/or scotopic vision.]

Troxler effect

[5.9.20] A fading of visual perception because of a stabilized retinal image. For example, the retinal blood vessels that lie in front of the retina are not normally seen, because […]

visual threshold in point vision

[5.11.2] The weakest illuminance at the eye that makes it possible to see a small source against a given background. The psychophysical definition is the point illuminance that gives 50 […]