How to convert lumens to lux

How to convert luminous flux in lumens (lm) to illuminance in lux (lx).

Lux: The amount of light that is cast on a surface is called illuminance, which is measured in lux. This can be thought of as light intensity within a specific area.  

Lumens: The total output of visible light from a light source is measured in lumens. Typically, the more lumens a light fixture provides, the brighter it is.

One lux is equal to one lumen per square meter (lux = lumens/m2). Essentially, as light travels from the emitter, it will disperse throughout an area. The further the light has to travel the more it will be dispersed. Therefore, the amount of lux in an area or on a surface can vary depending upon the distance the light travels and the angle at which it is dispersed.

Where the lumens provided by a given emitter are the same, light that travels less distance and/or is more narrowly focused will appear brighter because lux are concentrated in a smaller area than light that has traveled a greater distance and has been dispersed over a wider area. You can calculate lux from lumens and surface area. 

Lux and lumen units represent different quantities, so you can't convert lumens to lux.

• Lumens to lux calculation with area in square feet
• Lumens to lux calculation with area in square meters

Lumens to lux calculation formula

Lumens to lux 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

So 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

Lumens to lux 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

How to convert lux to lumens »