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

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 (ft^{2}):

*E*_{v(lx)} = 10.76391 ×* Φ*_{V(lm)} /* A*_{(ft}2_{)}

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 / ft^{2}

### 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 (m^{2}):

*E*_{v(lx)} = *Φ*_{V(lm)}* */* A*_{(m}2_{)}

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 / m^{2}

##### Example

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

*Φ*_{V(lm)} = 500 lux × 4 m^{2} = 2000 lm

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