This illuminance converter changes light falling on a surface between lux, kilolux, foot-candles, phots and nox. 1 lux is 1 lumen per square meter and 1 foot-candle is 1 lumen per square foot, so 1 fc = 10.7639 lux exactly from the definition of the foot.
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How to use the illuminance converter
- Enter the reading, for example 500 from a light meter in lux.
- In the illuminance converter, choose its unit and the target unit, such as lux to foot-candles.
- Read the illuminance converter result: 500 lux ≈ 46.45 fc.
For lux to foot-candles, divide by 10.7639 (or multiply by 0.092903). For foot-candles to lux, multiply by 10.7639.
What is illuminance?
Illuminance is the amount of light falling on a surface, measured in lux (lumens per square meter). Lighting standards in the US often use foot-candles; 1 foot-candle is about 10.764 lux.
Conversion formula
The illuminance converter stores every unit as a multiple of the base unit, the lux (lx). To convert:
value in target unit = value × (factor of source unit ÷ factor of target unit)
where each factor is the size of the unit in lux.
Common illuminance conversions
| From | To | 1 unit equals |
|---|---|---|
| lux (lx) | foot-candle (fc) | 0.09290304 fc |
| foot-candle (fc) | lux (lx) | 10.76391 lx |
| lux (lx) | phot (ph) | 0.0001 ph |
| phot (ph) | lux (lx) | 10,000 lx |
| kilolux (klx) | lux (lx) | 1,000 lx |
Illuminance converter worked example
Convert 25 lux to foot-candles:
- Factor of lx = 1 lx
- Factor of fc = 10.76391 lx
- 25 × 1 ÷ 10.76391 = 2.322576 fc
Illuminance unit reference
| Unit | Symbol | Group | Equals (lx) |
|---|---|---|---|
| Lux | lx | SI | 1 |
| Foot-Candle | fc | US/Imperial | 10.76391042 |
| Phot | ph | CGS | 10,000 |
| Nox | nx | SI | 0.001 |
| Kilolux | klx | SI | 1,000 |
Reverse factors for each illuminance unit
The illuminance converter reference table gives each unit in luxs. To go the other way, divide by that factor; the list below does the division for you.
- Foot-Candle (fc), US/Imperial: 1 fc = 10.76391 lx, so 1 lx = 0.09290304 fc.
- Phot (ph), CGS: 1 ph = 10,000 lx, so 1 lx = 0.0001 ph.
- Nox (nx), SI: 1 nx = 0.001 lx, so 1 lx = 1,000 nx.
- Kilolux (klx), SI: 1 klx = 1,000 lx, so 1 lx = 0.001 klx.
OSHA minimum lighting levels in lux and foot-candles
US workplace rules state lighting in foot-candles. The construction standard 29 CFR 1926.56 sets these minimums, shown here with the lux equivalents:
| Area (OSHA 29 CFR 1926.56) | Foot-candles | Lux |
|---|---|---|
| Concrete placement, excavation and waste areas, access ways | 3 | 32.3 |
| General construction area lighting | 5 | 53.8 |
| General construction plant and shops | 10 | 107.6 |
| First aid stations, infirmaries and offices | 30 | 322.9 |
Office design guides usually aim much higher than the OSHA minimum, typically several hundred lux on the desk. When a European specification gives lux, divide by 10.7639 to compare it with a US value in foot-candles.
Measuring illuminance
A light meter reads illuminance on its sensor, so hold it flat at the working surface, such as desk height, not pointed at the lamp. Illuminance from a point source falls with the square of distance: E = I ÷ d², with E in lux, I in candelas and d in meters. A 100 cd lamp gives 100 lux at 1 m but only 25 lux at 2 m. Use the luminous intensity converter for the source and the luminance converter for how bright the lit surface appears.
From lumens to lux
If you know a lamp’s output in lumens, you can estimate the average illuminance it gives. Spread 3,000 lm evenly over a 10 m² floor and the average is 300 lx, or about 27.9 foot-candles in the illuminance converter. Real rooms lose some light to walls, fixtures and dirt, so designers apply a utilization factor and a maintenance factor, and the true figure might be 60 to 70% of that.
For scale, the European standard EN 12464-1 asks for about 500 lx at office desks used for writing and reading. Overcast daylight is often around 10,000 lx, and bright sun can exceed 100,000 lx. In US units, an office target of 50 fc is about 538 lx.
One lux is one lumen per square meter; one foot-candle is one lumen per square foot. The factor between them, about 10.764, is simply the number of square feet in a square meter.
Related converters and calculators
Related light tools:
- Luminance converter: nits and fL
- Luminous intensity converter: cd and mcd
- Area converter: m² and ft²
- Image resolution converter: dpi and ppi
- Power unit converter: W and BTU/h
Sources
NIST Special Publication 811, Appendix B; OSHA 29 CFR 1926.56: Illumination.
Questions about this calculator
How many lux is one foot-candle?
10.7639 lux, because 1 ft² = 0.09290304 m² exactly.
How do I convert lux to foot-candles?
Divide by 10.7639. For example, 300 lux ≈ 27.9 fc.
How do I convert foot-candles to lux?
Multiply by 10.7639. For example, 50 fc ≈ 538.2 lux.
What is a phot?
The CGS unit of illuminance: 1 lumen per square centimeter, or 10,000 lux.
What lighting does OSHA require for offices?
29 CFR 1926.56 lists 30 foot-candles, about 323 lux, for construction site offices and first aid stations.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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