luminous intensity, usually of a light source, per unit solid angle; unit: lumen

Unit is erg/sec or watts.

The basic unit of optical power. Radiometric flux is expressed in watts. All wavelengths of the electromagnetic spectrum are included.

Flux is a measure of light power. Radiometric flux, expressed in watts, includes light at all wavelengths of the spectrum; ultraviolet (200 to 400 nm), visible (400 to 700 nm), and infrared (700 to 30000 nm). Luminous flux is a measure of photometric power. Photometric flux, expressed in lumens, includes only visible light, and is weighted to match the responsivity of the human eye, which is most sensitive to yellow-green.

The sum of all the lumens (lm) emitted by a source (see lumen).