How to convert lux to lumens

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

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

Lux to lumens calculation formula

Lux to lumens calculation 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)

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 luminous flux ΦV in lumens (lm) is equal to 0.09290304 times the illuminance Ev in lux (lx) times 4 times pi times the squared sphere radius r in feet (ft):

ΦV(lm) = 0.09290304 × Ev(lx) × 4⋅π⋅r(ft) 2

So

lumens = 0.09290304 × lux × (square feet)

or

lm = 0.09290304 × lx × ft2

Lux to lumens calculation 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 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 luminous flux ΦV in lumens (lm) is equal to the illuminance Ev in lux (lx) times 4 times pi times the squared sphere radius r in meters (m):

ΦV(lm) = Ev(lx) × 4⋅π⋅r 2

So

lumens = lux × (square meters)

or

lm = lx × m2

Example

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

ΦV(lm) = 500 lux × 4 m2 = 2000 lm

How to convert lumens to lux »


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