The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time.

A complete lighting unit consisting of a lamp(s) together with the parts designed to distribute the light, to position and protect the lamp and to connect the lamp to the power supply.

The amount of light emitted from a source (including that reflected from a surface). Luminance is measured in candela-per-square-meter (cd/m2).

Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light".

A luminescent solar concentrator is a device for concentrating solar radiation in particular, to produce electricity.

A measure of how well a light source produces visible light.

In photometry, luminous flux or luminous power is the measure of the perceived power of light.