๐ก Illuminance Converter
Convert between lux, footcandles (fc), and phot in real time. Useful for checking lighting fixture specs or reference brightness levels for photo and video shoots.
How to use
- Enter a value into any illuminance unit field (lux, fc, or phot).
- The converted values appear instantly in the other unit fields.
How the calculation works
Illuminance is how much light falls on a surface, measured in lux (lx). One lux is one lumen of luminous flux landing on one square metre. It describes how brightly a surface is lit, not how bright the light source itself is (that is lumens). A foot-candle (fc) is one lumen per square foot. A square foot is about 0.0929 mยฒ, so 1 fc โ 10.764 lx; the unit appears in US lighting standards and on film and photography equipment. The phot is the CGS unit, one lumen per square centimetre, or 10,000 lx. Double the distance from a light and the illuminance falls to a quarter (the inverse-square law). Because illuminance depends so strongly on distance and angle, choosing a light means thinking about where it will be mounted as well.
Worked example
A 500 lux desk surface in foot-candles 500 รท 10.7639 โ 46.5 fc In the other direction, the 50 fc quoted in a US document is 50 ร 10.7639 โ 538 lux. With the inverse-square law, a light giving 400 lux at 1 m gives 400 รท 4 = 100 lux at 2 m.
Things to be aware of
- Illuminance (lux) and luminous flux (lumens) are different quantities; bulb packaging normally quotes lumens.
- Illuminance varies with distance and angle; measure actual values with a light meter.
- Recommended light levels depend on the task. Check office and school standards in the relevant national standards.
- The phot is rarely used today.
FAQ
What's the difference between lux and footcandles (fc)?
Lux is the metric illuminance unit and fc is the imperial one. 1 fc is about 10.76 lux โ useful for comparing specs on imported lighting equipment.
Can this help compare office or factory lighting standards?
Yes โ it's useful for comparing local lighting standards given in lux against foreign standards given in fc.
What is a phot?
A phot is a CGS-system illuminance unit; 1 phot equals 10,000 lux. It's rarely used today.