In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit.
In photometry, luminous flux is the measure of the total perceived power of light while luminous intensity is a measure of the perceived power emitted by a light source in a particular direction per unit solid angle.
The luminous intensity distribution is another useful measurement for understanding how a light source behaves. It is a visual representation of how luminous intensity is distributed on a single or multiple planes, depending on the type of symmetry that the light has. A distribution plane shows the intensity of the source for all solid angles.