Troland (Td)
Troland (Td) :
A unit used in photometry to measure the amount of light reaching the retina of the eye. The "retinal illuminance" in trolands is equal to the luminance of the light shining on the eye, measured in candelas per square meter (cd/m2), multiplied by the area of the pupil open to the light, in square millimeters (mm2). This calculation makes the troland technically equal to the microcandela (µcd), a unit of luminous intensity, but retinal illuminance is a physical quantity different from luminous intensity. The unit is named for the American experimental psychologist Leonard T. Troland (1889-?)
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