# Candela to Watt Conversion

• nicolasmarie

#### nicolasmarie

I am working on rendering in Autocad and I have came across light. A point light representing a bulb has intensity measured in candela, default value 1500 Cd. I want to represent a normal bulb of 60 watts used for a room. Is there a way to calculate Candela to Watt? Can anyody help me on this please?

From the hyperphysics site http://hyperphysics.phy-astr.gsu.edu/hbase/vision/photom.html

The candela is the luminous intensity, in a given direction. of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

Also from hyperphysics,

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/lumpow.html

Thanks. If I grasp something out of the definition, the candela is 1/683 of a watt through I totally have no idea about the steradian d even less concerning the lumens. 1500 candela is 2.19 watt i.e for 60 watts, i need 41095 candela. Am i correct?

The luminous intensity in candela units is 1/683 per steradian where the steradian is the solid angle of one radian from the illuminating source. So you'll need to find the solid angle depending on what area you are illuminating. Check out this image:

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/isql.html#c1

Note that a 60 watt light bulb doesn't give 60 watts of light; there is going to be a lot of loss from heat. The box for the Philips soft white 60watt bulb I have in my hand says it has a brightness of 860 lumens. That's the value you should be using.