Which unit is used to measure the output of a light source?

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Multiple Choice

Which unit is used to measure the output of a light source?

Explanation:
Luminous flux—the total amount of visible light a source emits each second—is measured in lumens. This directly captures the light output of the source. Watts assess energy use, not brightness, so a higher wattage doesn’t necessarily mean more light because efficiency varies. Lux measures illuminance on a surface (lumens per square meter), which depends on distance and distribution, while candela indicates luminous intensity in a specific direction. Since we're talking about how much light the source puts out overall, lumens is the appropriate unit.

Luminous flux—the total amount of visible light a source emits each second—is measured in lumens. This directly captures the light output of the source. Watts assess energy use, not brightness, so a higher wattage doesn’t necessarily mean more light because efficiency varies. Lux measures illuminance on a surface (lumens per square meter), which depends on distance and distribution, while candela indicates luminous intensity in a specific direction. Since we're talking about how much light the source puts out overall, lumens is the appropriate unit.

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