What is the SI unit of luminous intensity?

The SI unit of luminous intensity is the candela (cd).

Luminous intensity is the measure of the amount of light that is emitted by a source in a particular direction. It is a fundamental quantity in photometry, which is the study of light and its measurement. The unit of 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 x 10^12 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The candela is one of the seven base units of the International System of Units (SI) and is defined in terms of the other base units. It is used in a variety of applications, such as lighting design, photography, and astronomy. For example, the brightness of a light bulb is measured in lumens, which is a measure of the total amount of light emitted by the bulb, and the luminous intensity of a star is used to determine its apparent magnitude, which is a measure of its brightness as seen from Earth.

In summary, the candela is the SI unit of luminous intensity, which is a measure of the amount of light emitted by a source in a particular direction. It is an important quantity in photometry and is used in a variety of applications, such as lighting design, photography, and astronomy.