Convert lux, foot-candles and other units of light on a surface.
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Drafted with AI assistance; calculations checked against primary sources and tested with the site's own code. About FlowUtil
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Illuminance is the light landing on a surface. One lux is one lumen per square metre, and one foot-candle is one lumen per square foot. Enter a value and pick the units. Lighting specs in the US often use foot-candles, while most other countries use lux.
1 fc = 1 ÷ 0.09290304 lx = 10.7639104 lx. 1 phot = 10,000 lx exactly.
| Lux (lx) | Foot-candles (fc) |
|---|---|
| 10 | 0.929 |
| 50 | 4.6452 |
| 100 | 9.2903 |
| 300 | 27.8709 |
| 500 | 46.4515 |
| 1,000 | 92.903 |
| 5,000 | 464.5152 |
| 10,000 | 929.0304 |
| 50,000 | 4,645.152 |
| 100,000 | 9,290.304 |
1500 lux → fc
500 lx = 46.45152 fc
500 lx = 46.45152 fc
250 fc → lux
50 fc = 538.195521 lx
50 fc = 538.195521 lx
330 fc → lux
30 fc = 322.917313 lx
30 fc = 322.917313 lx
41 phot → lux
1 ph = 10,000 lx
1 ph = 10,000 lx
5100000 lux → klux
100,000 lx = 100 klx
100,000 lx = 100 klx
6300 lux → lm/ft²
300 lx = 27.870912 lm/ft²
300 lx = 27.870912 lm/ft²
Luxlx
The SI unit of illuminance: 1 lm/m².
Foot-candlefc
1 lm/ft², or 10.7639104 lx. The usual US unit in lighting work.
Photph
1 lm/cm², exactly 10,000 lx. A CGS unit largely replaced by lux.
Milliluxmlx
0.001 lx, for very low light levels.
| Lux | Foot-candles |
|---|---|
| 10 | 0.93 |
| 50 | 4.65 |
| 100 | 9.29 |
| 300 | 27.87 |
| 500 | 46.45 |
| 1,000 | 92.90 |
| 10,000 | 929.0 |
The link is only the area of a square foot: 1 ft² = 0.09290304 m². So 1 fc = 1 ÷ 0.09290304 = 10.7639104 lx. For quick work, divide lux by 10 for a rough foot-candle figure, which reads about 8% high.
Lux and lumens are not the same kind of quantity, so no single factor links them. Lumens measure the light a lamp gives out. Lux measures how much of it lands on each square metre.
Lux = lumens ÷ area in m²
Spread 3,000 lumens evenly over 20 m² and you get 150 lux. Over 4 m², 800 lumens gives 200 lux. Real rooms give less, because walls and fittings absorb part of the light and the spread is never even. Use this as an upper limit, then allow for the room. Lamp power is a separate quantity again, and the power converter handles watts.
From a small source, illuminance follows the inverse square law: E = I ÷ d², with I in candelas and d in metres. An 800 cd spotlight gives 800 ÷ 3² = 89 lux at 3 m. Doubling the distance cuts the light to a quarter.
OSHA's construction rule, 29 CFR 1926.56, lists minimum levels in foot-candles. Here they are in both units:
| Area | Foot-candles | Lux |
|---|---|---|
| Concrete placement, excavation, access ways | 3 | 32 |
| General construction area | 5 | 54 |
| Indoor warehouses, corridors, exit ways | 5 | 54 |
| Plants and shops | 10 | 108 |
| First aid stations and offices | 30 | 323 |
OSHA proposed removing this rule in July 2025, so check the current text before relying on it.
Europe uses a different approach. EN 12464-1, the European workplace lighting standard, asks for 500 lux on writing, typing and reading tasks in offices. That is 46 fc, so a site office that meets the OSHA figure can still fall well short of the European one.
A foot-candle measures light arriving at a surface. A foot-lambert measures light leaving it, which is what the eye sees as brightness, so it is a unit of luminance. The two only meet through the surface's reflectance. One foot-lambert is 3.426 cd/m², and the luminance converter handles those units.
Older texts may also quote the phot, equal to 1 lumen per cm², or 10,000 lux. The nox, equal to 0.001 lux, is rarely used now.
A new installation reads higher than the same lamps a few years on, because output drops and fittings collect dirt. That is why EN 12464-1 sets a maintained value: the lowest level the installation must keep over its life. Quote two or three significant figures, as a hand meter does not justify more. If you are reporting several units at once, the SI units table lists the base definitions.
The factor comes from the exact foot: 1 ft = 0.3048 m, so 1 fc = 1 ÷ 0.09290304 lx. FlowUtil computes with that value and rounds only the display.
Illuminance varies with lamp age, surface reflectance and meter calibration, so two or three significant figures normally match the measurement.