Lumens vs lux — what is the difference?

A lumen describes total luminous flux emitted by a source. Lux describes how much of that flux reaches each square metre. In the ideal simplified relationship, 1 lx = 1 lm/m².

Practical example

A 20 m² room with a 150 lx target needs 3,000 lumens reaching the plane. With UF 0.65 and MF 0.80, the sources need about 5,769 lm. Six 1,000 lm fixtures give an estimated 156 lx.

Limitations

The simplified model does not know fixture intensity curves, individual surface reflectance, obstacles, glare or uniformity. A construction-ready design requires photometric data and suitable software.