What is the unit of measurement for Retinal Illumination?

Retinal illumination is specifically measured in trolands, which quantifies the amount of light reaching the retina. It takes into account both the luminance of an object (in candelas per square meter) and the area of the pupil (in square meters). The unique aspect of trolands is that it is a direct measurement of the light stimulus as perceived by the eye, facilitating the understanding of how different lighting conditions affect visual perception.

While candelas refer to the luminous intensity emitted in a particular direction and lux measures illuminance on a surface, neither directly accounts for the specific relationship between brightness and the viewer's pupil size, which is crucial for assessing retinal illumination. Foot-candles, on the other hand, are a non-metric unit also used for illuminance but do not provide the same direct relevance to retinal function as trolands do. Therefore, trolands are the most appropriate unit for measuring retinal illumination, aligning with the physiological aspects of how light interacts with the retina in a living eye.