Lux to Lumens Calculator
Convert illuminance in lux (lx) to luminous flux in lumens (lm). Enter the illuminance, 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 luminous flux in lumens. Everything runs locally in your browser.
Enter illuminance
Type the illuminance falling on the surface in lux (lx). A well-lit office sits around 300–500 lx, bright daylight can exceed 10,000 lx outdoors.
Pick units, enter area or radius
Choose Area in square feet or Area in square meters. Then enter either the surface area being lit (ft² / m²) or the radius of a sphere around the source (ft / m) — one of the two, not both.
Press Calculate, read lumens
Luminous flux appears in lumens (lm). Copy the value to your clipboard, switch the unit type and re-calculate to compare ft² and m² cases, or press Reset to start over.
How lux becomes lumens
- What is the lux to lumens formula with area in square meters?
- The luminous flux ΦV in lumens (lm) is equal to the illuminance Ev in lux (lx) times the surface area A in square meters (m²): ΦV(lm) = Ev(lx) × A(m²). For example, 500 lx over 4 m² gives 500 × 4 = 2000 lm.
- What is the lux to lumens formula with area in square feet?
- The luminous flux ΦV in lumens (lm) is equal to 0.09290304 times the illuminance Ev in lux (lx) times the surface area A in square feet (ft²): ΦV(lm) = 0.09290304 × Ev(lx) × A(ft²). The 0.09290304 factor converts square feet to square meters. For example, 5000 lx over 5 ft² gives 0.09290304 × 5000 × 5 = 2322.576 lm.
- How do I calculate lumens for a spherical light source?
- Light from an ideal point source spreads over a sphere of area 4π·r². With the radius in meters: ΦV(lm) = Ev(lx) × 4π · r(m)² — 100 lx at r = 1 m gives 100 × 4π ≈ 1256.6371 lm. With the radius in feet: ΦV(lm) = 0.09290304 × Ev(lx) × 4π · r(ft)² — 100 lx at r = 2 ft gives 0.09290304 × 100 × 16π ≈ 466.9816 lm.
- What is the difference between lux and lumens?
- Lux measures how much light lands on a surface; lumens measure the total luminous flux the source emits. One lux equals one lumen per square meter, so the same illuminance over a larger area (or a bigger sphere radius) means more lumens.
- Why does the same number give a different result in ft² vs m²?
- A square foot is only 0.09290304 of a square meter, so "5 square feet" is a much smaller area than "5 square meters" and needs less flux to reach the same lux. 500 lx reads 2000 lm over 4 m² but only 0.09290304 × 500 × 4 ≈ 185.8061 lm over 4 ft².
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 emit different flux than the sphere math suggests.