Lux to Candela Calculator
Convert lux to candela from the distance with the inverse-square law: cd = lux × d². Formula, worked example and a table of typical values.
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 |
|---|---|
| Illuminance (lux) | 25 |
| Distance from the source | 4 m |
| Angle of incidence (°) | 0 |
- I = E × d² / cos θ = 25 × 4² / 1 = 400 cd
Typical values
| Illuminance (lux) | Luminous intensity (cd) |
|---|---|
| 5 | 80 |
| 10 | 160 |
| 25 | 400 |
| 50 | 800 |
| 100 | 1,600 |
Other inputs are the same as in the worked example above.
Assumptions
- Treated as a point source: the distance should be at least five times the size of the source
- Distance is measured along the line from the source to the point
- No light is absorbed or reflected on the way
Valid when the distance is at least five times the source size. Near a large luminaire the inverse-square law overstates the lux.
Frequently asked questions
How do I convert Lux to Candela?
E = I × cos θ / d²; I = E × d² / cos θ; d = √(I × cos θ / E). Worked example: Illuminance (lux) 25, distance from the source 4 m, angle of incidence (°) 0 gives 400 cd.
What do I need to enter?
Enter luminous intensity (cd), illuminance (lux), distance from the source and angle of incidence (°). 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 candela and lux?
Candela is the light intensity of a source in one direction. Lux is the light arriving on a surface, and it falls with the square of the distance. The same source gives one quarter of the lux at twice the distance.
When is the inverse-square law valid?
When the source is small compared with the distance, at least about five times the size of the source. Close to a large luminaire it overstates the lux.
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: Lumens to LuxLumens to CandelaAGL Light Intensity at Distance
Opposite direction: Candela to Lux
Also see: Lumens to Candela Candela to Lumens Lux to Watts Watts to Lux
Formula guides: Point Illuminance FormulasLighting Formulas: Lux, Lumens and CandelaIlluminance and Luminance Converter
All 78 conversionsCandela, Lux and Distance (any two) in Elecmetric