Candela

Similar Terms: mcd

Candela, once known as 'candlepower', is a >SI unit of >Luminous Flux, a measure of brightness in a focused Beam as perceived by the human eye.

If a light source emits one candela of >Luminous Flux across a solid angle of one steradian, the total >Luminous Flux emitted into that angle is one >Lumen (1 cd·1 sr = 1 lm).

(A steradian is the >SI unit of solid angle, equal to the angle at the centre of a sphere subtended by a part of the surface equal in area to the square of the radius).

For example, a common candle emits light with a luminous intensity of roughly one candela.

Millicandela (mcd) in LEDs

You may see LED brightness measured in millicandela (mcd), which is a smaller unit of candela. There are 1000 millicandela in 1 candela.

To give you an idea, indicator LEDs are typically in the 50 mcd Range, and 'ultra-bright' LEDs can reach 15,000 mcd. A typical 100 watt incandescent bulb will produce around 1700 lumens. If that light is radiated equally in all directions, it will have a brightness of around 135,000 mcd. Focused into a 20° Beam, it will have a brightness of around 18,000,000 mcd.