About Illuminance
Illuminance measures the amount of light falling on a surface. Lux is the SI unit, widely used in lighting design and photography.
Footcandles are used in the US, while phots and nox are older metric units for very high and very low light levels respectively.
Pro Tips
Office lighting typically requires 300–500 lux; direct sunlight is around 100,000 lux.
Multiply footcandles by 10.764 to get lux — a quick rule for US to metric conversion.