What is the base unit of luminous intensity?

The base unit of luminous intensity is the candela. Luminous intensity is a measure of the amount of light emitted by a source in a particular direction and is a fundamental metric used in lighting design and various applications involving light sources.

The candela is defined as the intensity of light emitted in a specific direction by a source that produces monochromatic radiation at a frequency of 540 terahertz and has a radiant intensity of 1/683 watt per steradian. This definition highlights how the candela relates to both the perception of brightness and the physics of electromagnetic radiation.

In contrast, the watt is a unit of power and measures the rate at which energy is used or produced. Lux measures illuminance, which is the amount of light received on a surface area, indicating how well-lit a space is. A lumen quantifies the total amount of visible light emitted by a source, which is directly related to luminous flux rather than intensity. Thus, while these other units relate to different aspects of light and its measurement, the candela specifically addresses the intensity of light emitted in a particular direction.