Lumens to Lux Calculator
Lux and foot-candles from a light’s lumens spread over an area or in a beam, or the lumens needed for a lux level you choose.
Result
Illuminance, lux: 86.1113
The ideal case: all the stated light spread evenly. Real rooms lose some to walls and fittings, and the light is never perfectly even.
- Illuminance, foot-candles
- 8
- Lumens
- 800
https://calcgallery.com/electronics/lumens-to-lux-calculator/
Results come from the published equations applied to the values you enter. They are not electrical design, conductor sizing, laboratory safety or medical guidance. Weather indices describe a standard person in standard conditions and are not a forecast. Where codes apply, local rules vary and must be checked. Read the full disclaimer
How to use the Lumens to Lux Calculator
- Choose lux from lumens over an area, the lumens needed for a lux level you pick, or the lux a beam gives at a distance.
- Enter the lumens from the lamp's packaging or data, and the area, or the beam angle and distance.
- Read the illuminance in lux and foot-candles, or the lumens needed.
The formulas
over an area: lux = lumens × share ÷ area in m² foot-candles = lumens × share ÷ area in ft²lumens needed: lumens = lux × area ÷ sharefor a beam of full angle θ: solid angle Ω = 2π × (1 − cos(θ ÷ 2)) steradians intensity I = lumens ÷ Ω candela illuminance E = I ÷ distance² lux, on the beam's axisThese follow from the SI definitions: a lumen is a candela times a steradian, and a lux is a lumen per square metre.
Limits
The area result is an average for light spread evenly over the surface; real lighting is brighter under the lamp and dimmer at the edges. The beam result assumes the same intensity across the whole cone, and a distance large compared with the lamp. Lamp data often gives a beam angle to half the peak intensity, so a real beam’s edges are softer than the drawing.
With your numbers
- Illuminance = lumens × share ÷ area = 800 lm × 100% ÷ 9.2903 m² = 86.1113 lx
Quick reference
The ideal case: all the stated light spread evenly. Real rooms lose some to walls and fittings, and the light is never perfectly even.
| Example | Result |
|---|---|
| 800 lm over 4 m² | Illuminance, lux: 200 |
| 1,000 lm over 100 ft² | Illuminance, lux: 107.6391 |
| Lumens for 300 lx over 12 m² | Lumens: 3,600 |
| Lumens for 300 lx over 12 m², half reaching it | Lumens: 7,200 |
| 400 lm in a 36° beam at 2 m | Illuminance, lux: 325.1811 |
| 800 lm in a 120° beam at 2.5 m | Illuminance, lux: 40.7437 |
Common questions about the Lumens to Lux Calculator
- What is the difference between lumens and lux?
- Lumens measure the light a lamp gives out in total. Lux measure how much of it lands on each square metre of a surface: one lux is one lumen per square metre. The same 800 lm spread evenly over 4 m² is 200 lx, and over 8 m² only 100 lx.
- How do lux and foot-candles relate?
- A foot-candle is one lumen per square foot. A square foot is 0.09290304 m², so 1 foot-candle is about 10.764 lux and 1,000 lm spread over 100 ft² is 10 foot-candles, about 107.6 lux. The page gives both.
- How does a beam angle change the result?
- A narrow beam puts the same lumens into a small cone, so the intensity in candela is high and the spot it lights is small and bright. 400 lm in a 36° beam gives about 1,301 candela, which is about 325 lux on the axis 2 m away. Illuminance then falls with the square of the distance: twice as far, a quarter of the lux.
- How many lumens does a room need?
- Choose the lux you want, from a lighting guide or a standard for the task, and the page works out the lumens that would reach it over the area. It does not recommend a level. Because walls, shades and dirt absorb some light, set the share of light reaching the area below 100% if you know how much is lost.