Which of the following units measures light output?

The unit that measures light output is the lumen. This measurement quantifies the total amount of visible light emitted by a source, which makes it central to understanding how much light a particular bulb or fixture produces. Lumen is a standard measurement used in various lighting applications to convey the brightness of a light source, providing consumers with a clear indication of the light output they can expect.

In contrast, candlepower measures the intensity of light emitted in a specific direction rather than the total light output. Lux measures illuminance, which is the amount of light that falls on a given area, rather than the total light produced. Kelvin is a unit of measurement related to color temperature, indicating the warmth or coolness of the light emitted, but does not describe its brightness. Thus, lumen is the appropriate choice when looking for a measure of light output.