Lumens to Lux Calculator
Convert lumens to lux from the area the light covers: E = lumens / m². Formula, worked example and a table. Lumens alone cannot give lux.
Try your own numbers
Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
Open in the calculator with these values
Formula
Worked example
| Input | Value |
|---|---|
| Luminous flux (lm) | 3,000 |
| Area | 20 m² |
| Fraction of lumens reaching the surface | 1 |
- E = Φ × u / A = 3,000 × 1 / 20 = 150 lux
- Footcandles = lux / 10.7639 = 13.935
Typical values
| Luminous flux (lm) | Illuminance (lux) |
|---|---|
| 500 | 25 |
| 1,000 | 50 |
| 3,000 | 150 |
| 5,000 | 250 |
| 10,000 | 500 |
Other inputs are the same as in the worked example above.
Assumptions
- Light is spread evenly over the area
- u is the fraction of lamp lumens that reach the surface
Lux is lumens per square metre. For a room, use the utilisation and maintenance factors, or the lumen method for a luminaire count.
Frequently asked questions
How do I convert Lumens to Lux?
E = Φ × u / A; Φ = E × A / u; A = Φ × u / E (1 fc = 10.7639 lx). Worked example: Luminous flux (lm) 3,000, area 20 m², fraction of lumens reaching the surface 1 gives 150 lux.
What do I need to enter?
Enter luminous flux (lm), illuminance (lux), area and fraction of lumens reaching the surface. Leave blank the value you want to find, and the form solves for it. Change the unit of a value with its selector and the result stays the same.
What is the difference between lumens and lux?
Lumens measure the total light a source gives out. Lux is lumens per square metre arriving on a surface, so it depends on the area the light spreads over. The same lamp gives more lux on a small area and less on a large one.
Why is the fraction of lumens reaching the surface 1?
The worked example assumes every lumen lands on the surface, which is the ideal case. In a real room some light is lost to walls, the luminaire and dirt, so use a utilisation and maintenance factor below 1.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. Check design values against the standard and the equipment data you work to.
Related
Next steps in a design: Lux to WattsLighting LevelCandela to Lux
Opposite direction: Lux to Lumens
Also see: Candela to Lux Lux to Candela Lumens to Candela Candela to Lumens
Formula guides: Lighting Formulas: Lux, Lumens and CandelaPoint Illuminance FormulasIlluminance and Luminance Converter
All 78 conversionsLumens, Lux and Area (any two) in Elecmetric