Light

Lumen

The SI unit of luminous flux.

Foot-candle

A unit of illumination on a surface that is everywhere one foot from a uniform point source of one candela and equal to one lumen incident per square foot.

Lambert

A unit of luminance or brightness equal to 0.32 candela per square centimeter.

Foot-lambert

A unit of luminance or brightness equal to 0.32 candela per square foot.

Candle

A unit of luminous intensity used prior to 1948, equal to the luminous intensity of a wax candle of standard specifications.

Candle power

Luminous intensity expressed in candelas

Lux

The SI unit of illumination, equal to one lumen per square meter.

Candela

The basic SI unit of luminous intensity.

Luminous intensity

The luminous flux emitted per unit solid angle by a light source expressed in candelas

Luminance

The quantitative measure of brightness of a light source or an illuminated surface, equal to the luminous intensity per unit projected area of the source or surface viewed from given direction.

Luminous flux

The rate of flow of visible light per unit time. Expressed in lumens

Brightness

The sensation by which an observer is able to distinguish between differences in luminance.