They don't measure the same thing. Lumens measures light output,and candela measures light on a surface.
1 candela= lumen/steradian
Does one Candela (SI Unit for lumious intesnity) = lumens per metre squared,
i.e. 1 Cd = 1 lum/m^2
if not, what is the relationship between candela and lumens?
3 answers
Then, in the light intensity equation E=L/r^2, where E is illumination, L is luminous intensity and r is distance, what are the units of each factor?
Candela refers to lumens emitted per steradian in a particular direction by a pointlike source. It is related to the old unit "candle". It does not refer to the lumens hitting a surface per area, that is called illuminance, and is measured in lux.
In the equation E = L/r^2, E (illuminance) is in lux, L is in candelas and r is in meters.
Recommended reading:
http://en.wikipedia.org/wiki/Candela
In the equation E = L/r^2, E (illuminance) is in lux, L is in candelas and r is in meters.
Recommended reading:
http://en.wikipedia.org/wiki/Candela
2 answers