Posted by **Kurst** on Saturday, March 15, 2008 at 10:22pm.

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?

- Physics -
**bobpursley**, Saturday, March 15, 2008 at 11:32pm
They dont measure the same thing. Lumens measures light output,and candela measures light on a surface.

1 candela= lumen/steradian

- Physics -
**Kurst**, Sunday, March 16, 2008 at 6:04am
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?

- Physics -
**drwls**, Sunday, March 16, 2008 at 7:11am
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

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