Lux to Candela Calculator
Convert illuminance in lux (lx) to luminous intensity in candela (cd) at a given distance from a point light source. Enter the lux value, the distance, select feet or meters, and press Calculate — the luminous intensity comes from Iv(cd) = 0.09290304 × Ev(lx) × (d(ft))² or Iv(cd) = Ev(lx) × (d(m))². Everything runs locally in your browser.
Enter illuminance
Type the illuminance Ev in lux (lx) — how much light actually lands on the surface, the number a lux meter reads. Zero or any positive value is accepted; zero lux gives zero candela.
Enter the distance and pick the unit
Type the distance d from the light source to the surface and select ft (feet) or m (meters) in the unit dropdown. The distance must not be negative; zero is allowed and yields zero candela, because intensity grows with the square of the distance in this direction.
Press Calculate, read candela
The luminous intensity Iv appears in the result field in candela (cd). Press Calculate again after changing any value, or press Clear to reset everything and start over.
Lux to candela calculation
- Lux to candela formula with distance in meters
- The luminous intensity Iv in candela (cd) is equal to the illuminance Ev in lux (lx), times the square distance from the light source d² in square meters (m²): Iv(cd) = Ev(lx) × (d(m))². For example, 500 lx measured 3 m from a point source gives 500 × 3² = 4500 cd.
- Lux to candela formula with distance in feet
- The luminous intensity Iv in candela (cd) is equal to 0.09290304 times the illuminance Ev in lux (lx), times the square distance d² in square feet (ft²): Iv(cd) = 0.09290304 × Ev(lx) × (d(ft))². The factor 0.09290304 converts square feet to square meters (1 ft² = 0.09290304 m²). A surface lit to 100 lx at 5 ft implies 0.09290304 × 100 × 25 ≈ 232.2576 cd.
- What is the relation between lux and candela?
- One lux is the illuminance produced by one candela falling on a surface one meter away: 1 lx = 1 cd/m². Measured in feet, 1 lx at 1 ft corresponds to 0.09290304 cd, exactly the square-foot-to-square-meter factor.
- Why does the distance get squared?
- Light from a point source spreads over a sphere whose area grows with the square of the radius (inverse-square law). Doubling the distance quadruples the implied candela: 500 lx at 2 m points to 2000 cd, while 500 lx at 4 m points to 8000 cd.
- How accurate is this calculator?
- Results use the ideal point-source formulas above with full precision up to 8 decimals (trailing zeros trimmed). Real lamps are not points — reflectors and diffusers spread light unevenly — so treat the result as an engineering estimate, and remember it applies to a surface facing the source straight on.
- Can I convert candela back to lux?
- Yes, algebraically: Ev(lx) = Iv(cd) / (d(m))² for meters, or Ev(lx) = 10.76391 × Iv(cd) / (d(ft))² for feet — the inverse direction is available on our candela to lux calculator page.
Privacy: every calculation runs in your browser tab — no value you type is sent anywhere and nothing is stored after the tab closes. Results assume an ideal point source measured straight-on; verify real installations with a lux meter. See also the candela to lux calculator.