Lumens to Lux Converter
Lumens measure how much light a source gives out; lux measures how much of it lands on each square meter. Enter the lumens plus either the lit area or the beam angle and distance, and get lux and foot-candles with the math shown.
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100% = ideal; 50–80% allows for fixture and wall losses
Full cone angle from the spec sheet
How to use the Lumens to Lux Converter
- Enter the lumens from the bulb or fixture spec, or tap a preset.
- Pick a method: Illuminated area if light spreads over a known surface, or Beam angle and distance for a directional light.
- Fill in the area (m² or ft²), or the beam angle and the distance to the surface.
- Lower the percentage if part of the light is lost in the fixture or on dark walls.
- Read the lux and foot-candles, then check the table for other areas or distances.
Lumens to lux formulas
lux = lumens ÷ area (m²) · foot-candles = lumens ÷ area (ft²)
One lux is one lumen falling on one square meter. To convert, you need to know how much surface the light is spread over. There are two common ways to get that area:
1. From a known area
If the light covers a room, a table or a wall evenly, divide the lumens by its area. Example: 1,600 lm over a 100 ft² room = 1,600 ÷ 9.29 m² = 172 lux (16 foot-candles).
2. From beam angle and distance
A directional lamp lights a circle whose size grows with distance:
- Spot radius
r = d × tan(θ ÷ 2), where θ is the full beam angle and d the distance. - Spot area
A = π × r². - Average illuminance
lux = lumens ÷ A.
Example: a 400 lm, 36° spotlight at 2 m gives r = 2 × tan 18° = 0.65 m, A = 1.33 m², so about 300 lux on average. The tool also shows the on-axis value from the light's intensity in candela, I = lm ÷ 2π(1 − cos(θ/2)), and E = I ÷ d², which is slightly higher in the middle of the spot.
Doubling the distance spreads the same lumens over four times the area, so lux drops to a quarter (the inverse-square law).
How bright is that? Typical lux levels
| Situation | Lux | Foot-candles |
|---|---|---|
| Full moon on a clear night | about 0.1–0.3 | about 0.01–0.03 |
| Hallway, stairs | 100 | 9 |
| Living room, general | 150–300 | 14–28 |
| Kitchen, bathroom | 300 | 28 |
| Office desk, reading, kitchen worktop | 500 | 46 |
| Detailed work, workshop bench | 750–1,000 | 70–93 |
| Overcast daylight outdoors | about 1,000–10,000 | about 90–900 |
| Direct sunlight | about 100,000 | about 9,300 |
Getting a realistic answer
- Not all lumens arrive. Shades, reflectors and diffusers absorb some light and dark walls reflect little back. Setting "Light reaching the surface" to 50–80% gives a more realistic room estimate.
- Use the beam angle from the spec sheet, usually defined where intensity falls to half of the center value. Light outside it is not counted here, so real spill makes the edges a little brighter.
- Check with a meter. A phone light meter app or a handheld lux meter is the quickest way to confirm your calculation.
Frequently asked questions
How do you convert lumens to lux?
Divide the lumens by the lit area in square meters: lux = lm ÷ m². 800 lumens spread evenly over 10 m² gives 80 lux. If your area is in square feet, multiply it by 0.0929 first.
How many lux is 1,000 lumens?
It depends on the area. 1,000 lm over 1 m² is 1,000 lux, over 10 m² it is 100 lux and over 20 m² it is 50 lux. Lumens alone cannot be turned into lux.
How do I convert lumens to lux with a beam angle?
Work out the spot the beam makes: radius = distance × tan(beam angle ÷ 2), area = π × radius². Then lux = lumens ÷ area. A 400 lm, 36° spotlight at 2 m lights a spot about 1.3 m wide at roughly 300 lux on average.
What is the difference between lumens, lux and foot-candles?
Lumens measure total light output. Lux is lumens per square meter on a surface, and foot-candles are lumens per square foot. One foot-candle equals about 10.764 lux.
Why is the center brighter than the average?
Over a flat surface, the middle of the beam is closest to the lamp and hit head-on, while the edges are farther away and hit at an angle. The tool shows both the average over the spot and the on-axis value.
Why is my measured lux lower than calculated?
Real fixtures lose light in reflectors, diffusers and lenses, dark walls absorb light, and beams are not perfectly even. Setting the 'light reaching the surface' percentage to 50–80% gives a more realistic estimate.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.