Illuminance Converter
Illuminance is how much light lands on a surface, measured in lux in metric and foot-candles in the United States. One foot-candle equals 10.764 lux, which is simply one lumen spread over a square foot rather than a square metre.
For reference: an office desk is usually specified at 300 to 500 lux, an overcast day is around 1,000 lux, and direct sunlight is above 30,000.
| Lux | Foot-candles | Phot |
|---|---|---|
| 50 lx | 4.6452 fc | 0.005 ph |
| 100 lx | 9.2903 fc | 0.01 ph |
| 300 lx | 27.8709 fc | 0.03 ph |
| 500 lx | 46.4515 fc | 0.05 ph |
| 750 lx | 69.6773 fc | 0.075 ph |
| 1000 lx | 92.903 fc | 0.1 ph |
| 10000 lx | 929.0304 fc | 1 ph |
How to convert lux to foot-candles
Choose the two units
Pick the unit your meter reports and the unit your specification is written in.
Enter the reading
Type the value into either field and the other converts live as you type.
Compare against typical levels
Use the note under the result and the table below to see how the number compares to office, overcast, and daylight levels.
Copy the result
Copy the converted value straight into your lighting plan or report.
Why use this tool
Six illuminance scales
Lux, kilolux, foot-candles, phot, milliphot and nox all convert between each other in either direction.
Typical levels built in
Office, overcast and daylight reference points sit next to the result, which is usually what the number is being checked against.
Illuminance only, deliberately
Lumens and candela measure different things and need an area or a distance to relate, so they are left out rather than converted with a hidden assumption.
Exact foot-candle factor
Uses 10.763910417 rather than a rounded 10.76, so large values stay accurate.
Runs entirely in your browser
Nothing you type is uploaded or stored.
About this tool
Illuminance is the amount of light arriving at a surface, and it is the number that lighting standards, workplace regulations and photography guides are written in. Metric countries measure it in lux, defined as one lumen per square metre. The United States measures it in foot-candles, defined as one lumen per square foot. Because a square foot is smaller than a square metre, one foot-candle is a denser amount of light: 10.763910417 lux.
The older centimetre-gram-second units still turn up in optics literature. A phot is one lumen per square centimetre, which makes it 10,000 lux, and a milliphot is 10 lux. Nox is a rarely used unit equal to one thousandth of a lux, kept here because it appears in low-light and night-vision specifications. All of these measure the same quantity, so any one converts into any other by a fixed multiple.
What this tool will not do is convert lumens or candela, and that is deliberate. Lumens measure total light output from a source and candela measure intensity in a direction. Turning either into lux requires knowing the area lit or the distance to the surface, so a converter that offered it would be quietly inventing a number. For general unit work there is the unit converter, for screen and print sizing the typography unit converter, and for checking text legibility against a background the contrast checker.
Frequently asked questions
- How many lux is one foot-candle?
- One foot-candle is 10.763910417 lux. The factor is the number of square feet in a square metre, because both units are one lumen spread over that area.
- Why can I not convert lumens to lux here?
- Lumens measure the total light a source puts out, while lux measures how much lands on a surface. Converting between them needs the area being lit, which only you know. Any tool that does it without asking is assuming a number.
- What lux level should an office be?
- General office work is usually specified at 300 to 500 lux, which is roughly 28 to 46 foot-candles. Detailed work such as drafting is often set higher, at 750 to 1,000 lux.
- What is a phot?
- A phot is one lumen per square centimetre, from the older centimetre-gram-second system. It equals 10,000 lux, so it is a very large unit that mainly appears in optics literature.
- How bright is daylight in lux?
- An overcast day is around 1,000 lux, full daylight without direct sun runs 10,000 to 25,000 lux, and direct sunlight can exceed 100,000 lux.
- Is my data uploaded anywhere?
- No. The conversion runs in your browser and nothing you type leaves your device.
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