Quote Originally Posted by seventhchild
it is converted into light not heat .watts is watts its true but ya'll need to understand that this is a measure of energy used not of light output.when the light fixture converts electricity to light some of the energy is lost as heat. incandescent bulbs lose most of that energy as heat....LEDs not so much..... i think this may be called lighting efficiency or something like that ..........the point being that fixtures that convert energy into light with less heat generation will heat the room less.
This is close, it's not efficiency but efficacy, the power or capacity to produce a desired effect. Efficiency in this case relates to power input versus energy losses in the system, whereas efficacy would be how much light is produced per unit of input power.

About 70% of the power that goes into an HID system is lost as heat, with the rest being produced as light. With LED, about 10% of the input power is lost as heat, with the rest producing light.