A lumen (lm) is a unit of luminous flux: light output weighted according to the photopic response of human vision. Lumens describe a different quantity from lux, which measures light arriving per unit area.
Lumens versus lux
A fixture’s total lumen output does not establish the illuminance at an actor’s mark. The beam distribution, distance and modifiers determine how much of that output reaches the area you are lighting. An optic can concentrate light without creating additional luminous flux.
Reading specifications
Check whether a figure describes the complete fixture, a bare emitter, or only the flux within a defined beam or field. Those figures are not directly interchangeable. For filming, compare lux at useful distances alongside coverage and colour performance.
Practical example
Two fixtures can deliver similar total lumens while producing very different centre readings. A narrow spotlight concentrates its output; a broad soft source spreads light over a wider area. Choose using the coverage the shot needs, not the lumen number alone.
Related terms
Lux · Beam Angle · Watt