What unit measures luminous flux?

Luminous flux is a measure of the total amount of visible light emitted by a source per unit of time, and it is quantified in lumens. The lumen is the SI unit that represents the quantity of light produced by a source in all directions within a specific time period. It provides a standard way to quantify the intensity of light, making it fundamental in various applications such as lighting design, photography, and illumination measurement.

Understanding the other options helps clarify the context further. A luminaire refers to a complete lighting unit that can include lamps, fixtures, and other components necessary for lighting. It is not a unit of measurement but rather the assembly of elements that collectively provide light.

A foot candle, while related to illumination, measures illuminance — the amount of light falling on a surface — specifically in terms of lumens per square foot. It does not represent luminous flux directly.

Candlepower, also known as luminous intensity, measures the amount of light emitted in a particular direction, rather than the total light output. Therefore, while it is related to light measurement, it does not capture the overall luminous flux as comprehensively as lumens do.

Thus, the lumen stands out as the correct answer, as it is specifically designed to quantify luminous