Light Intensity Converter
Convert light intensity between lux, foot-candles, lumens per sq meter, and phot.
Includes reference values for offices, photography studios, and daylight.
Type in any field — the others update instantly.
Light intensity (illuminance) measures how much light falls on a surface. All conversions use lux as the base unit.
Unit definitions:
- 1 lux = 1 lumen per square meter (lm/m²)
- 1 foot-candle = 10.7639 lux (1 lumen per square foot)
- 1 phot = 10,000 lux (CGS unit, 1 lumen per cm²)
- 1 nox = 0.001 lux (used for very low light)
Typical illuminance levels:
| Condition | Lux | Foot-candles |
|---|---|---|
| Full moonlight | 0.25-1 | 0.023-0.093 |
| Street lighting | 10-50 | 0.93-4.65 |
| Office lighting | 300-500 | 27.9-46.5 |
| Overcast day | 1,000-2,000 | 93-186 |
| Direct sunlight | 50,000-100,000 | 4,650-9,300 |
Metric (lux) vs Imperial (foot-candles): Most of the world uses lux. The US commonly uses foot-candles for architectural lighting design.
The key idea behind every unit here is that they measure light landing on a surface, not light coming out of a bulb. A 1,000-lumen bulb throws a fixed amount of light, but the lux reading on your desk depends on how far away it is and how the light is spread. Move twice as far from a small source and the illuminance drops to a quarter, the inverse-square law, which is why pulling a desk lamp back a foot makes a bigger difference than it seems like it should.
This is the distinction that trips people up when buying lights: lumens rate the source, lux rate the result at a given spot. A grow light advertised at huge lumens can still leave plants short if it is mounted too high, and a camera light meter reads in lux or foot-candles precisely because what matters for exposure is the light reaching the subject. If you are checking whether a room is bright enough, lux at the work surface is the honest number; the box’s lumen rating only tells you the bulb’s potential.
How we build and check this converter
This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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