What unit is used to measure luminous intensity?

The correct unit used to measure luminous intensity is the candela. Luminous intensity is defined as the amount of light that is emitted from a source in a particular direction, and the candela quantifies this intensity. It is one of the seven base units in the International System of Units (SI) and is specifically used to describe how bright a light source appears in terms of its output in a specific direction.

In contrast, the lumen measures the total amount of visible light emitted by a source. It represents the total luminous flux, which takes into account all directions, rather than the intensity in a specific direction. The watt is a unit of power and measures the rate of energy use, which is not directly related to the perception of light. Lastly, lux is a unit of illuminance, which indicates how much luminous flux is spread over a given area, rather than measuring the intensity of light itself. Understanding these distinctions highlights why the candela is the accurate measure for luminous intensity.