The power of light, often refered to as luminous intensity, is described as its luminous intensity. Whereas brightness is is related to human perception of of the light, luminous intensity describes its energy flux.
The following units are used to describe the luminous intensity of light:
 
Candela (cd)- Unit of luminous intensity, describing the intensity of a light source in a specific direction. The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The candela was based on an older unit, the candlepower, which was referenced to the luminous intensity of a "standard candle" of known composition.see more

Lumen (lm) – Unit of the quantity of luminous flux emitted within a unit solid angle (one steradian) by a point source with one candela intensity in all directions.

Lux (lx) - Unit of Illuminance, e.g. the amount of light per square meter incident on a surface.