Answer: The SI unit of luminous intensity is the candela (cd).
Luminous intensity measures the brightness or amount of light emitted in a particular direction from a light source.
The candela is defined as 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 formula to calculate luminous intensity (Iv) is:
where:
- Iv is the luminous intensity measured in candela (cd),
-
is the luminous flux (total amount of visible light emitted) measured in lumens (lm), and -
is the solid angle subtended by the light source, measured in steradians (sr).
This formula describes how luminous intensity is calculated based on the rate of change of luminous flux with respect to solid angle. In essence, it quantifies how much visible light is emitted per unit solid angle from the light source.