The Answer
The Short Answer
Compare bulbs at a similar lumen output, then look at their actual wattage and rated life. A lower-wattage LED uses less electricity for each hour it runs, but payback is quickest for frequently used lamps and slower where a light is rarely switched on or an unusual replacement is expensive.
The Full Explanation
Calculate the Running-Cost Difference
Subtract the LED wattage from the old lamp wattage, multiply by operating hours, divide by 1,000 to convert to kilowatt-hours, and multiply by the electricity unit rate on your bill. Ofgem notes that savings vary with the home, equipment, and the way it is used, so update the calculation when prices or usage change.
Compare Equal Light Output
Use lumens to compare the amount of light, then watts to compare power demand. ENERGY STAR's consumer guide, for example, uses about 800 lumens as the minimum replacement output for a traditional 60W incandescent bulb; the LED's actual wattage varies by product.
Include Purchase and Replacement Costs
DOE says good-quality LED products typically have much longer rated lives than incandescent lamps, but drivers, electronics, heat, and operating conditions also affect service life. Include purchase price and any compatibility costs, and do not assume the rated hours are a guaranteed calendar lifetime.
Related Questions
Sources
- 1
- 2LED Basics
U.S. Department of Energy
- 3Learn About Brightness
ENERGY STAR