Which unit represents luminous flux?

Which unit represents luminous flux?

• A. Watt (W)
• B. Lux (lx)
• C. Lumen (lm)
• D. Candela (cd)

Answer: (C)

Luminous flux is a measure of the total amount of visible light emitted by a source per unit of time, and it is specifically quantified in lumens (lm). One lumen represents the light output of a source that produces a uniform illumination of one candela over a solid angle of one steradian. This measurement accounts for the sensitivity of the human eye to different wavelengths of light, emphasizing the perception of brightness. In contrast, watts measure power and can include all forms of energy, not exclusively light, making them inappropriate for measuring luminous flux. Lux measures illuminance, which is the amount of luminous flux per unit area and is expressed as lumens per square meter. Candela measures luminous intensity, which describes light emitted in a specific direction, but does not account for the total light output. Thus, when referencing the total light emitted, lumen is the appropriate unit to express 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 specifically quantified in lumens (lm). One lumen represents the light output of a source that produces a uniform illumination of one candela over a solid angle of one steradian. This measurement accounts for the sensitivity of the human eye to different wavelengths of light, emphasizing the perception of brightness.

In contrast, watts measure power and can include all forms of energy, not exclusively light, making them inappropriate for measuring luminous flux. Lux measures illuminance, which is the amount of luminous flux per unit area and is expressed as lumens per square meter. Candela measures luminous intensity, which describes light emitted in a specific direction, but does not account for the total light output. Thus, when referencing the total light emitted, lumen is the appropriate unit to express luminous flux.