Lumens to Lux Calculator
Convert luminous flux in lumens (lm) to illuminance in lux (lx). Enter the luminous flux, select the area unit type, then enter a radius for a spherical light source or a surface area for any light source — and press Calculate to get the illuminance in lux. Everything runs locally in your browser.
Enter luminous flux
Type the luminous flux of the light source in lumens (lm). A typical 60 W incandescent bulb emits around 800 lm, a modern 10 W LED bulb around 800–900 lm.
Pick units, enter area or radius
Choose Area in square feet or Area in square meters. Then enter either the surface area the light falls on (ft² / m²) or the radius of a sphere around the source (ft / m) — one of the two, not both.
Press Calculate, read lux
Illuminance appears in lux (lx). Copy the value to your clipboard, switch the unit type and re-calculate to compare ft² and m² readings, or press Reset to start over.
How lumens become lux
- What is the lumens to lux formula with area in square meters?
- The illuminance Ev in lux (lx) is equal to the luminous flux ΦV in lumens (lm) divided by the surface area A in square meters (m²): Ev(lx) = ΦV(lm) / A(m²). For example, 1000 lm spread over 10 m² gives 1000 / 10 = 100 lx.
- What is the lumens to lux formula with area in square feet?
- The illuminance Ev in lux (lx) is equal to 10.76391 times the luminous flux ΦV in lumens (lm) divided by the surface area A in square feet (ft²): Ev(lx) = 10.76391 × ΦV(lm) / A(ft²). The 10.76391 factor converts square feet to square meters. For example, 1000 lm over 10 ft² gives 10.76391 × 1000 / 10 = 1076.391 lx.
- How do I calculate lux for a spherical light source?
- Light from an ideal point source spreads over a sphere of area 4π·r². With the radius in meters: Ev(lx) = ΦV(lm) / (4π · r(m)²) — 1000 lm at r = 1 m gives 1000 / (4π) ≈ 79.5775 lx. With the radius in feet: Ev(lx) = 10.76391 × ΦV(lm) / (4π · r(ft)²) — 900 lm at r = 2 ft gives 10.76391 × 900 / (16π) ≈ 192.7271 lx.
- What is the difference between lumens and lux?
- Lumens measure the total luminous flux a source emits; lux measures how much of that flux lands on a surface — one lux equals one lumen per square meter. The same bulb produces fewer lux the larger the area (or the bigger the sphere radius) it has to cover.
- Why does the same number give a different result in ft² vs m²?
- A square foot is smaller than a square meter, so the same flux over "10 square feet" is more concentrated: the square-feet formula multiplies by 10.76391 (= 1 / 0.092903). 1000 lm over 10 of either unit reads 100 lx in square meters but 1076.391 lx in square feet.
Privacy: every calculation runs in your browser tab — no value you type is sent anywhere. Copy buttons use your clipboard only. Sphere results assume an ideal point source radiating evenly in all directions; real fixtures with reflectors or lenses concentrate light and read higher directly in the beam.