Lumen second

The term "lumen second" refers to a unit of measurement used in photometry, which is the science of measuring visible light. Specifically, the lumen (lm) is the SI unit of luminous flux, a measure of the perceived power of light. A "lumen second" would represent a quantity of light emitted over a time period of one second. In practical terms, if a light source emits one lumen of light continuously for one second, it would deliver one lumen second of luminous flux.