Illuminance Converter
Convert between lux, foot-candles and phot.
Results update as you type.
How it works
An illuminance converter restates how much light falls on a surface in a different unit, moving between lux, foot-candles and the older phot. It reduces your figure to lux, the SI unit for illuminance of one lumen per square metre, then scales out to the unit you choose, so one mechanism covers lighting design, photography, workplace-safety standards and horticulture alike. This matters because illuminance is quoted in different units on either side of the Atlantic and across disciplines. Lighting engineers and most of the world specify workspace and street lighting in lux; North American lighting practice and much photographic literature use foot-candles, the illuminance of one lumen per square foot; older scientific texts occasionally use the phot from the centimetre-gram-second system. A workplace standard given in lux and a fixture rated in foot-candles cannot be compared until both share one unit. The convert-through-lux method is used because every illuminance unit has a fixed ratio to the lux — one foot-candle is about 10.764 lux, matching the number of square feet in a square metre, and one phot is exactly 10,000 lux, one lumen per square centimetre — so pivoting through it keeps results exact and needs only one factor per unit. Lighting designers, architects, photographers, safety officers and growers all rely on an illuminance converter whenever a light-level figure arrives in an unfamiliar unit, so they can meet standards and set exposures correctly.
Convert to lux via known factors, then to the target unit
The input is multiplied by its unit's fixed number of lux to express the illuminance in lux, then divided by the target unit's lux value to complete the conversion. Because a foot-candle is one lumen per square foot and a lux is one lumen per square metre, their ratio is exactly the number of square feet in a square metre, about 10.764; the phot is one lumen per square centimetre, exactly 10,000 lux, so every unit has a fixed ratio.
Source:International System of Units (SI) — NIST
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter value, from and to.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Converted illuminance updates instantly as you type — no button to press.
Frequently asked questions
How do I convert foot-candles to lux?
Multiply the foot-candle figure by about 10.764 to get lux, because a lux is one lumen spread over a square metre while a foot-candle is one lumen over a square foot, and a square metre holds about 10.764 square feet. So 50 foot-candles is about 538 lux. To reverse it, divide lux by 10.764. The factor is geometric, coming purely from the area conversion.
What is a good lux level for an office?
General office work typically calls for around 300 to 500 lux, while detailed tasks such as drafting or fine assembly may need 750 to 1,000 lux. Corridors and storage areas can be much lower, around 100 lux. Expressed in foot-candles, 500 lux is about 46 foot-candles. Lighting standards vary by country and task, so check the relevant local code, but these ranges are widely used guidance.
What is a phot?
A phot is a unit of illuminance from the older centimetre-gram-second system, equal to one lumen per square centimetre. Because a square centimetre is tiny compared with a square metre, one phot is a very intense 10,000 lux. It rarely appears in modern practice but shows up in older scientific literature, so the converter includes it to translate legacy figures into familiar lux or foot-candles.
Is illuminance the same as brightness?
Not quite. Illuminance, measured in lux or foot-candles, is the amount of light landing on a surface. Brightness as a perception relates more closely to luminance, the light reflected or emitted toward the eye from a surface, measured in candelas per square metre. This converter handles illuminance only, which is what light meters read and what workplace and photographic standards specify.
Why convert illuminance through lux?
The lux is the SI unit for illuminance, one lumen per square metre, so every other illuminance unit has a fixed, exactly defined ratio to it. Using it as the pivot means the converter needs only one factor per unit rather than a separate rule for each pair, keeps results exact, and matches the unit that international lighting standards and photometry equations use for specifying light levels.