The troland (symbol Td), named after Leonard T. Troland, is a unit of conventional retinal illuminance. It is meant as a method for correcting photometric measurements of luminance values impinging on the human eye by scaling them by the effective pupil size. It is equal to retinal illuminance produced by a surface whose luminance is one nit when the apparent area of the entrance pupil of the eye is 1 square milimeter.
The troland typically refers to the ordinary or photopic troland, which is defined in terms of the photopic luminance:
where L is the photopic luminance in cd m-2 and p is pupil area in mm2
A scotopic troland is also sometimes defined:
where L′ is the scotopic luminance in cd m-2 and p is pupil area in mm2
Read more about Troland: Conversions To Other Units, Conversions From Other Units, Physical Quantities, Unit System, Unit Status, Basic Unit Dimensions, Comparisons, See Also