Luminous flux incident on the retina. The simplified formula is
T = LS
where
L is the luminance of the stimulus in cd/m
2 and
S is the area of the pupil in mm
2. The retinal illuminance
T is then given in trolands. Retinal illuminance decreases with age due to absorption of the lens and to a reduction in pupil size. It may represent a reduction of as much as 30 fold in an 80-year-old eye as compared to a 20-year-old eye.
Syn. retinal illumination.
See troland;
vignetting.