How to convert illuminance in lux (lx) to luminous flux in lumens (lm).
You can calculate lumens from lux and surface area. Lux and lumen units represent different quantities, so you can't convert lux to lumens.
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
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
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
