Like all lightbulbs, light-emitting diodes (LEDs) produce illumination by turning a given amount of electric current into light. LEDs perform this conversion more efficiently than standard incandescent bulbs: According to the U.S. Department of Energy, a typical Energy Star-rated LED uses 20 to 25 percent of the energy that an incandescent bulb uses; the LED lasts up to 25 times longer, too (see References 5). The amount of light a bulb generates can be measured in a unit called lumens. Electrical power is measured in a unit called watts. Due to their methodology of converting electricity into light, LED bulbs feature a higher ratio of lumens to watts than incandescent bulbs.
A lumen is a measurement of light directly relevant to human beings. Instead of trying to measure the number of photons or raw radiated energy, the lumen scale describes the amount of light, or brightness, that the human eye perceives. All modern lightbulb packaging shows the number of lumens the bulb produces. An average 100-watt incandescent bulb, for example, produces about 1,600 lumens. (See References 2.)
A watt is a measurement of electrical power, formally equal to the amount of energy in 1 ampere of current flowing at 1 volt. A lightbulb that is rated at, say, 200 watts uses more electricity to produce light than a bulb rated for 100 watts. The benefit, however, is that the 200-watt bulb produces significantly more light than the lower-rated bulb. The relative efficiency of different lightbulbs can be gauged by comparing how many lumens they produce for every watt of electrical power.
Watts and Lumens in LEDs
LEDs that are bright enough to replace incandescents for household use—that is, producing the same number of lumens as standard 40- or 60-watt bulbs—typically only use 9 to 12 watts. The U.S. Department of Energy advises that consumers who want to replace a 60-watt bulb should look for an LED that produces close to 800 lumens; for a 40-watt bulb, look for 450 lumens (see References 2). As of March 2011, manufacturers were just starting to produce high-powered LEDs for the home. Philips has developed a 60-watt replacement that only uses 12 watts of power (see References 7), while GE has developed a 40-watt replacement that uses only 9 watts of power (see References 4).
Lumens don’t describe the quality of the generated light—its color, tone or other variables. Some people find they don’t like the light that certain LED bulbs produce, describing it as “cold,” “pale” or “dim.” The biggest challenge for LED manufacturers is creating bulbs that mimic conventional ones in shape and light quality. As of March 2011, compact fluorescent lamps (CFLs), which use 25 percent of the energy of standard incandescents, were still more versatile and cost-effective than LEDs (see References 3).
How LEDs Work
When electrical current runs through an LED, the electrons in the current flow into a semiconductor material containing electron “holes”—spaces waiting to be filled with electrons. When the electrons fill those holes, energy is released as photons, or light that is emitted outward, turning the LED into a lightbulb. In contrast, incandescent bulbs generate light from the electrical resistance of a metal filament. The resistance method requires more electrical energy to heat up the filament to a point that it glows and emits light. (See References 6.)
Credit to; Aaron Zvi, Demand Mediahttp://homeguides.sfgate.com/lumens-vs-watts-led-bulbs-78825.html