the sensitivity of a material to light; specifically a numerical value indicating the speed at which a photographic film or sensor reacts to light

An instrument used to measure the intensity of light or to compare the luminous intensity of two light sources; luminometer.

A unit of measurement for the optical power of a lens or curved mirror, equal to the reciprocal of the focal length in meters.

luminosity; the degree of brightness of a light source

an instrument used to measure the intensity of light

The degree of brightness of a light-emitting body.