What is the difference between luminance and brightness?
The terms “luminance” and brightness” are often used interchangeably although they have different meanings. Humans are more sensitive to light of some wavelengths (quanta of different energy) than others. Luminance is a physical measure which weights the effects of different wavelengths by human sensitivity. Brightness is a psychological experience. (The first rule of psychophysics is don’t confuse physical variables with psychological ones!). For any given color, a higher luminance will appear brighter. However, the relationship between luminance and brightness varies across colors, so two colors of identical luminance may not be equally bright. In daylight conditions, the brightest lights fall in the yellowish-green range. Blues, violets and reds are least bright. It is a common fallacy that blue is the brightest light at night. In dim illumination, viewers switch from cone (photopic) to rod (scotopic) vision, and sensitivity shifts to lower wavelengths. The brightest light changes t
