Which unit expresses the total light emitted by a source?

Which unit expresses the total light emitted by a source?

• A. Illuminance
• B. Candela
• C. Lux
• D. Lumen

Answer: (D)

The total light emitted by a source is captured by luminous flux, which is measured in lumens. This unit sums up all the light the source produces in every direction per unit time, giving a single, direction-independent quantity for how much light the source emits overall. Illuminance, measured in lux, describes how much of that light actually lands on a surface, and depends on distance and surface area. Candela represents luminous intensity in a specific direction, not the total emitted light. Lux is the illuminance on a surface, i.e., lumens per square meter, not the source’s total output. So the lumen is the unit that best expresses the total light emitted by a source.

The total light emitted by a source is captured by luminous flux, which is measured in lumens. This unit sums up all the light the source produces in every direction per unit time, giving a single, direction-independent quantity for how much light the source emits overall.

Illuminance, measured in lux, describes how much of that light actually lands on a surface, and depends on distance and surface area. Candela represents luminous intensity in a specific direction, not the total emitted light. Lux is the illuminance on a surface, i.e., lumens per square meter, not the source’s total output.

So the lumen is the unit that best expresses the total light emitted by a source.