Luminous intensity is a measure of the amount of light emitted in a particular direction from a light source. It is defined as the amount of luminous flux (the total amount of visible light emitted by a source) per unit solid angle, where the solid angle is measured in steradians (sr).
The SI unit for luminous intensity is the candela (cd), which is defined as the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 terahertz (THz) and that has a radiant intensity in that direction of 1/683 watt per steradian.
Luminous intensity is important in the field of lighting design and is used to determine the appropriate lighting levels for various tasks and environments. It is also used in the measurement of the brightness of light sources such as light bulbs, lamps, and LEDs.