Candela to Lux Calculator
Convert luminous intensity in candela (cd) to illuminance in lux (lx) at a given distance from a point light source. Enter the candela value, the distance, select feet or meters, and press Calculate — the illuminance comes from Ev(lx) = 10.76391 × Iv(cd) / (d(ft))² or Ev(lx) = Iv(cd) / (d(m))². Everything runs locally in your browser.
Enter luminous intensity
Type the luminous intensity Iv in candela (cd) — how strong the source shines in the direction of the surface. Zero or any positive value is accepted; zero candela gives zero lux.
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 be greater than zero, because illuminance is divided by the square of the distance.
Press Calculate, read lux
The illuminance Ev appears in the result field in lux (lx), rounded to two decimals. Press Calculate again after changing any value, or press Clear to reset everything and start over.
Candela to lux calculation
- Candela to lux formula with distance in meters
- The illuminance Ev in lux (lx) is equal to the luminous intensity Iv in candela (cd), divided by the square distance from the light source d² in square meters (m²): Ev(lx) = Iv(cd) / (d(m))². For example, a 100 cd point source measured 2 m away gives 100 / 2² = 25 lx.
- Candela to lux formula with distance in feet
- The illuminance Ev in lux (lx) is equal to 10.76391 times the luminous intensity Iv in candela (cd), divided by the square distance d² in square feet (ft²): Ev(lx) = 10.76391 × Iv(cd) / (d(ft))². The factor 10.76391 converts square feet to square meters (1 ft² = 0.09290304 m²). A 100 cd source 2 ft away gives 10.76391 × 100 / 4 ≈ 269.1 lx.
- What is 1 candela in lux?
- At 1 meter from a point source, 1 candela produces exactly 1 lux — that is the definition: 1 lx = 1 cd/m². At 1 foot the same source gives 10.76391 lx, because a square foot is a smaller area than a square meter.
- 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 quarters the illuminance: the same 100 cd gives 25 lx at 2 m but only 6.25 lx at 4 m.
- How accurate is this calculator?
- Results use the ideal point-source formulas above and are rounded to two decimal places (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 on a surface facing the source straight on.
- Can I convert lux back to candela?
- Yes, algebraically: Iv(cd) = Ev(lx) × (d(m))² for meters, or Iv(cd) = Ev(lx) × (d(ft))² / 10.76391 for feet. This page computes only the candela → lux direction.
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.