Lux:
The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a model of human visual brightness perception, standardized by the CIE and ISO. In English, “lux” is used as both the singular and plural form. The word is derived from the Latin word for “light”, lux. [Wikipedia]
Noted in “Blue eyes may be better for reading in dim light than brown eyes,” Michael Le Page, NewScientist (6 February 2024, paywall):
After the volunteers sat in darkness for 30 seconds, the researchers gradually increased the brightness of the lighting until the participants were able to read a sequence of letters on a wall 3 metres away. Those with blue eyes needed a light level of 0.7 lux on average, compared with 0.82 lux for those with brown eyes.
