Lux to Candela Calculator
Convert lux (lx) to candela (cd) at a distance: cd = lx × d² (meters) or cd = lx × d(ft)² ÷ 10.76391. Reverse candela to lux. Runs locally in your browser.
Trust summary Engine tested · Specification checked · v1.1.0
- Input interpretation
- Enter values to calculate.
- Result
- —
- Model
- Luminous intensity from illuminance and distance, or illuminance from intensity and distance.
- Scope
- Point source
- Verification
- Engine tested · Specification checked · v1.1.0
- Named expert review
- Optional · Not performed
- Specification basis
- Inverse-square law: I = E × d² for SI units
- 1 m² = 10.76391 ft²
Formulas
Core equations used by this calculator.
How to use
Choose direction and units
lx → cd or cd → lx, with distance in meters or feet.
Enter lux (or candela) and distance
Use the lux-meter reading and the source-to-surface distance.
Read candela or illuminance
Result follows the inverse-square law for a point source on a facing surface.
Example calculations
Common configurations with formula and result.
500 lx · 3 m
Default (meters)
500 lx · 10 ft
Default (feet)
1 lx · 1 m
Definition check
400 lx · 5 m
Spotlight check
cd → lx
500 cd · 3 m
Related light quantities (not interchangeable)
Common values at a glance.
| Quantity | Unit | What it measures |
|---|---|---|
| Illuminance | lx (lm/m²) | Light landing on a surface |
| Luminous intensity | cd (lm/sr) | Light in a direction from the source |
| Luminous flux | lm | Total light output |
| Luminance | cd/m² (nit) | Brightness of a surface as seen |
Lux to Candela calculator specification
Version 1.1.0 · Engine tested
- Engine tested 4 published cases
- Named expert review Not performed
- Calculation version 1.1.0
- Definition
- Lux (lx) is illuminance on a surface (lm/m²); candela (cd) is luminous intensity in a direction. For a point source and a surface facing the light, I = E × d². With d in meters: cd = lx × d². With d in feet: cd = 0.09290304 × lx × d(ft)² (same as lx × d(ft)² ÷ 10.76391).
- What it calculates
- Luminous intensity from illuminance and distance, or illuminance from intensity and distance.
- Inputs
- Lux (lx) or candela (cd)
- Distance in meters or feet
- Outputs
- Candela (lx → cd) or lux (cd → lx)
- Formula
I=E·d² (m); I=E·d²/10.76391 (ft)- Assumptions
- Point source
- Surface facing the source (normal incidence)
- Units
- lx, m → cd
- lx, ft → cd
- Boundary conditions
- d = 0 → intensity 0 in UI product path; avoid physically
- Example
- 500 lx, 3 m → 4500 cd
- Validation cases
4 published on this page
- 500 lx, 3 m → 4500 cd
- 500 lx, 10 ft → ≈ 4645.15 cd
- 1 lx, 1 m → 1 cd
- 500 cd, 3 m → lx → ≈ 55.5556 lx
- Specification basis
- Inverse-square law: I = E × d² for SI units
- 1 m² = 10.76391 ft²
- Calculation version
- 1.1.0
Background
Interpretation and common distinctions.
Convert lux (lx) to candela (cd) at a known distance using the inverse-square law.
I((cd)) = E((lx)) × d((m))² I((cd)) = (E((lx)) × d((ft))²)/10.76391
Default: 500 lx · 3 m → 4500 cd.
Lux vs candela vs luminance
| Quantity | Unit | Measures |
|---|---|---|
| Lux (lx) | lm/m² | Illuminance — light on a surface |
| Candela (cd) | lm/sr | Intensity — light from the source in a direction |
| Luminance | cd/m² | How bright a surface looks (not this calculator) |
At 1 m, under the ideal model, 1 lx ↔ 1 cd numerically. Farther away, the same lux implies higher source intensity.
Notes
- Point-source model; extended luminaires need photometry for design work.
- Oblique incidence multiplies illuminance by cosα.
- Candlepower is an older name for candela.
Related tools
Other calculators in this family: Candela to Lux, Lumen to Candela, Lumen to Lux, Foot-Candles to Lux .
Frequently asked questions
Key distinctions behind the calculation.
How do I convert lux to candela?
Multiply by distance squared: cd = lx × d² with d in meters. With d in feet: cd = lx × d(ft)² ÷ 10.76391.
What is the difference between lux and candela?
Lux is how bright a surface is (illuminance). Candela is how intense the source is in a direction. Distance links them for a point source.
Is candela per square metre the same as this?
No. cd/m² is luminance (surface brightness, sometimes called nit). This tool converts illuminance (lux) to intensity (candela) using distance.
Why is there a factor for feet?
Lux is per square meter. Converting the inverse-square law when d is in feet uses 1 m² = 10.76391 ft² → factor 0.09290304.
Is 1 lx at 1 m equal to 1 cd?
Yes, under the point-source / normal-incidence model: I = E × d² → 1 × 1² = 1 cd.
Do I need beam angle?
Not for lux ↔ candela at a known distance. Beam angle is needed when relating candela to total lumens.
Can I convert candela back to lux?
Yes — use cd → lx: lx = cd ÷ d² (meters), or lx = 10.76391 × cd ÷ d(ft)².
What about oblique surfaces?
Illuminance falls by cos(α) when light hits at angle α. This calculator assumes the surface faces the source.