The efficiency of an illuminant is determined by the ratio of accepting energy to yielding luminous flux.
The unit of measurement is lumen per watt (lm/W)

Below are listed some comparative values for common illuminants in the order of their efficiency

Energy that is not dissipated into light produces heat.
As a result, LED-lights produce more heat than the currently most effective halogen bulbs (03.2007).

It is a mystery to us how some suppliers of LED-lights explain their allegation that LED have a better degree of efficiency than halogen bulbs (according to their allegation, no heat is produced).