The luminous intensity in definition is the luminous flux (ø) emitted within a solid angle (Ω). It expresses the capacity of a point light source to illuminate in a given direction. It is expressed in candela (cd). A common candle emits light with a luminous intensity of nearly 1cd.

Here θ is the apex angle which is the angular measure of the intersection of the lines defining the apex of the light emitted by the LED source.

Luminous flux is the amount of energy radiated out of an LED per unit time. It is expressed in lumens (lm).