What is illuminance (lux) and what are typical lighting levels for different spaces?

Illuminance measured in lux (lumens per square meter) quantifies the amount of light falling on a surface. Typical recommended levels are: corridors 100-150 lux, offices 300-500 lux, retail spaces 300-750 lux, detailed assembly work 750-1000 lux, and operating theaters 10,000+ lux. Proper lighting levels ensure visual comfort, productivity, and safety while avoiding excessive energy consumption.