What is the unit used to measure light intensity?

The unit used to measure light intensity is candlepower, which specifically quantifies the intensity of light emitted in a particular direction. It is based on the luminous intensity of a light source, measured in candelas, which represent the amount of light emitted by a source in a specified direction. This unit is particularly useful in applications where the directional quality of the light is essential, such as in the design of lighting fixtures and the assessment of visibility in an area.

Lumen measures the total amount of visible light emitted by a source, while footcandle represents the illuminance on a surface area, reflecting how much light is reaching that surface. Watts, on the other hand, measure electrical power and are not directly related to light intensity. Each of these other units serves a distinct purpose within the realm of lighting and energy but does not specifically measure the intensity of light in the same directional context that candlepower does.