Incandescent bulbs are rated by wattage, a measure of how much power is consumed. This is because incandescent design involves a specific correlation between the power input and the light output. LEDs, on the other hand, can output the same amount of light with a reduction of up to 90% in the power consumed.
For this reason, LEDs are rated by lumen output in addition to wattage input. LEDs are much more efficient than incandescent bulbs, which waste much of the power input as heat. Furthermore, the technology is continually improving, making the usage of lumens as a measure of brightness even more necessary.The more lumens, the brighter the light will be.
To estimate the lumen rating of a new LED bulb needed to replace an old incandescent bulb, use the chart at right. For example, a 60W incandescent bulb should be replaced by an 800 lumen LED bulb.