Which term best describes the total luminous output of a lighting fixture?

• A. Luminous efficacy
• B. Luminous intensity
• C. Quantity of light
• D. Illuminance

Answer: (C)

The thing being described is the total amount of light a fixture emits in all directions per unit time. That overall light output is known as luminous flux, measured in lumens. Among the given options, the phrase that best matches this idea is “Quantity of light,” since it captures the total light produced by the fixture rather than how bright it appears in one direction or how efficiently it uses power.

To contrast the other terms: luminous intensity refers to light emitted in a particular direction (measured in candela), not the total across all directions. Illuminance is how much light lands on a surface (lux), which depends on distance and area. Luminous efficacy describes how efficiently electrical power is converted into light (lumens per watt), not the total amount of light output. So, the option describing the overall amount of light produced aligns with the concept of total luminous output.