Luminous flux is defined as what?

• A. The path the light takes from the lamp
• B. The total amount of light emitted by a source, measured in lumens
• C. The color of light measured in kelvin
• D. The duration of light emission measured in seconds

Answer: (B)

Luminous flux is the total amount of light emitted by a source as perceived by the human eye, summed across all directions and expressed in lumens. It’s a photometric measure that weights radiant energy by the eye’s sensitivity, so it correlates with how bright the light appears. This distinguishes it from radiant energy (measured in watts), which is about energy rather than perceived brightness, and from color temperature (kelvin) or duration (seconds). If you need brightness in a specific direction, you’d look at luminous intensity, and for light on a surface, illuminance in lux.