The candela (cd) is the standard SI derived unit used in physics to measure luminous intensity. It quantifies the measure of light emitted by a source in a specific direction. Luminous intensity is a key component in characterizing light sources, differentiating it from total luminous flux, which measures the total amount of visible light energy passing through a surface area. The candela allows for the objective quantification of how brightly a light appears to the human visual system, forming the basis for illuminance measurements and overall photometric studies in engineering and scientific instrumentation.