Illuminance

Lumens are not lux — why a desk needs 500 lux

A light-bulb box shouts “800 lumens,” “1600 lumens” — and it feels obvious that a bigger number means a brighter room. It is a trap. Whether you see well is decided by the lux: how much of that emitted light actually lands on your desk. This is the story of illuminance — the inverse-square law, why a full moon gives a quarter of a lux yet still lets you walk at night, and why the office standard is exactly 500 lux.