A method you can check
LED replacements can reduce the electrical power needed for a given lighting task, but selecting the right bulb is more than choosing the smallest wattage. The replacement needs to provide appropriate brightness, fit the fixture, and be compatible with dimmers or enclosed fixtures where those requirements apply.
Watts are power; lumens describe light output
Wattage indicates electrical power use. Lumens describe the amount of visible light emitted. When comparing bulbs, use lumens and the manufacturer's equivalent-lighting information to select a similar level of brightness, then use wattage for the energy calculation.
Estimate the annual difference
Subtract the replacement wattage from the old bulb wattage, multiply by the number of bulbs and hours used, and divide by 1,000 to convert watt-hours to kWh. Multiply annual kWh saved by your electricity rate to estimate annual energy-cost savings. Actual use depends on how long the lights are on throughout the year.
Account for purchase cost
A simple payback estimate divides the total cost of replacement bulbs by the annual energy-cost saving. It does not include bulb life, labor, disposal, changes in electricity prices, or discounting. If the annual saving is zero or negative, there is no energy-cost payback under the entered assumptions.
Make the comparison fair
- Compare similar brightness and beam spread.
- Use the same count of lighting points.
- Estimate realistic daily runtime for each room.
- Check dimmer compatibility and fixture temperature ratings.
- Do not assume every label's “equivalent wattage” is a precise performance guarantee.
Use the LED Lighting Savings Calculator to show both estimated energy savings and a simple upfront-cost payback.
Related resources
Continue with the Electricity Cost Calculator, the Home Energy Planner, or the Appliance Comparison Calculator depending on the question you are trying to answer.
References and further reading
ENERGY STAR's brightness guide explains why lumens describe light output while watts describe electrical power. The U.S. Department of Energy also provides guidance on choosing energy-efficient light bulbs, including fixture and dimmer compatibility.
Use these sources to compare lighting characteristics; use your own electricity rate and real usage hours for the cost estimate. Product availability and local labels vary by country.