How Much Heat Does a Light Bulb Produce?
An incandescent light bulb emits 90 percent of the energy it uses as heat. Thus, a 75-watt light bulb produces 68 watts as heat. Most of the power used goes to heating up a tungsten filament, which glows at 4,600 degrees Fahrenheit.
A fluorescent light bulb does not use resistance to produce light, but ultraviolet collisions converted to visible light by phosphor inside the bulb. Only 60 percent of the energy is lost as heat in the collisions, so a 75-watt bulb produces 45 watts as heat. This heat is spread out over the larger area of the bulb, so it is not felt as strongly as in an incandescent bulb.