In lighting we refer to it as a particular lamps efficacy.

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.