Incandescent light bulb efficiency. Animation showing the energy efficiency of an incandescent light bulb. Only 5% of the electrical energy of this 100 watt light bulb is converted into light, producing 1600 lumens of illumination. 95 watts are lost as heat. Incandescent bulbs have much lower energy efficiency and shorter lifespans than LED lamps and fluorescent lamps. See K004 8879 and K004 8875 for comparison.