Lumens, Watts etc - conversion factors

Has anyone got a conversion factor for Lumens to Watts? It seems to be the way of rating LEDs used in torches.
You can't convert one to the other!

Lumens is the amount of light emitted, watts is the amount of power used.

If you have an inefficient bulb, you will get less lumens per watt. IF you have an efficient bulb, you will get more lumens per watt. Thus, the efficiency of the transducer dictates the conversion, and as you have not listed the efficiency of the transducer, you cannot convert one to the other.

One is a unit of light, one of power. Simple!
There is no direct conversion.

A Watt is an electrical unit which, over time, has come to signify a certain brightness of bulb. These new fangled fluorescent bulbs (and, now, LEDs) have messed up that relationship.

A Lumen is the modern SI unit of brightness. This used to be measured in candlepower, but the unit has not been in general use for years, other than on some high powered torches sold by the DIY chains.

Try Google but be prepared for a conversation as deep and convoluted as the current Arrse thread on the "Speed of Dark"!

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