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Luminous flux incident on the retina. The simplified formula is
T = LSwhere L is the luminance of the stimulus in cd/m2 and S is the area of the pupil in mm2. 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.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann