Lumens to lux calculator

Luminous flux in lumens (lm) to illuminance in lux (lx) calculator and how to calculate.

Enter the luminous flux in lumens, select area unit type, enter radius in meters for spherical light source or surface area

in square meters for any light source and press the Calculate button to get the illuminance in lux:

Lumens to lux calculation formula

Calculation with area in square feet

The illuminance E_v in lux (lx) is equal to 10.76391 times the luminous flux Φ_V in lumens (lm) divided by the surface area A in square feet (ft²):

E_v(lx) = 10.76391 × Φ_V(lm) / A_(ft2₎

For a spherical light source, the area A is equal to 4 times pi times the squared sphere radius:

A = 4⋅π⋅r ²

The illuminance E_v in lux (lx) is equal to 10.76391 times the luminous flux Φ_V in lumens (lm) divided by 4 times pi times the squared sphere radius r in feet (ft):

E_v(lx) = 10.76391 × Φ_V(lm) / (4⋅π⋅r_(ft)²)

So

lux = 10.76391 × lumens / (square feet)

or

lx = 10.76391 × lm / ft²

Calculation with area in square meters

The illuminance E_v in lux (lx) is equal to the luminous flux Φ_V in lumens (lm) divided by the surface area A in square meters (m²):

E_v(lx) = Φ_V(lm) / A_(m2₎

For a spherical light source, the area A is equal to 4 times pi times the squared sphere radius:

A = 4⋅π⋅r ²

So the illuminance E_v in lux (lx) is equal to the luminous flux Φ_V in lumens (lm) divided by 4 times pi times the squared sphere radius r in meters (m):

E_v(lx) = Φ_V(lm) / (4⋅π⋅r_(m) ²)

So

lux = lumens / (square meters)

or

lx = lm / m²

Example

What is the luminous flux on a surface of 4 square meters and illuminance of 500 lux?

Φ_V(lm) = 500 lux × 4 m² = 2000 lm