Luminous flux converter

Light bulbs are rated by the light they emit, in lumens, rather than by the power they draw, since an LED gives the same light for a fraction of the watts: 800 lm is what a 60 W incandescent bulb produced and an LED delivers it for 8–10 W, 1,600 lm replaces a 100 W bulb. The ratio, lumens per watt, is the luminous efficacy: 10–15 lm/W for incandescent, 80–120 lm/W for LED, and 683 lm/W is the theoretical ceiling for green light. A candle emits about 12 lumens.