Illuminance Converter
Convert light levels between lux and foot-candles - handy for lighting design, photography and checking a room is bright enough.
About the Illuminance Converter
This tool converts illuminance - the amount of light falling on a surface - between lux, foot-candles and phot. Lux is the SI unit (one lumen per square metre), foot-candles are common in North American lighting practice, and phot is a CGS unit you meet occasionally in older references.
How to use it
- Enter the reading you have into its field, such as a light-meter value in lux.
- Read the equivalent in foot-candles or phot.
- Convert either way when a lighting standard quotes the unit you do not use.
The everyday conversion is between lux and foot-candles: 1 foot-candle equals about 10.764 lux, the same factor as square feet to square metres, since both relate to the area term. For reference, a bright office is around 500 lux (about 46 foot-candles) and direct sunlight can exceed 100,000 lux. Note that illuminance measures light arriving at a surface, not perceived brightness or light leaving a source. The converter runs entirely in your browser and stores nothing you enter.
Frequently asked questions
How many lux are in a foot-candle?
One foot-candle equals about 10.764 lux. That is the same numeric factor as square feet to square metres, because both describe light per unit area.
How much illuminance does a typical office need?
General office work is usually lit to around 300 to 500 lux (about 28 to 46 foot-candles), while detailed tasks may call for more.
What is the difference between lux and lumens?
Lumens measure total light output from a source, while lux measures how much of that light lands on a surface, spread over its area. One lux is one lumen per square metre.
What is a phot?
A phot is a CGS unit of illuminance equal to one lumen per square centimetre, so one phot equals 10,000 lux. It is rarely used today but appears in older texts.