How this calculator works
A bulb's energy use is its watts divided by 1,000 (to get kilowatts) times the hours it is on. Over a year that is watts ÷ 1,000 × hours a day × 365. Multiply the kWh by your price per kWh for the cost, and subtract the LED figure from the old figure for the saving. Dividing the cost of the new bulbs by the monthly saving gives the payback time.
Worked example: 20 bulbs changed from 60 W to 9 W, on 3 hours a day. Each old bulb uses 60 × 3 × 365 ÷ 1,000 = 65.7 kWh a year, each LED 9.9 kWh. For 20 bulbs the saving is 1,116.9 kWh, which is $189.87 a year at 17 cents per kWh. 20 LED bulbs at $3 cost $60, so they pay for themselves in about 3.8 months. A single bulb saves $9.49 a year.
Assumptions and sources
The assumptions behind your numbers (prices, efficiencies and usage) are listed in the notes directly under your results, and they update when you change an input.
The formula and a worked example are shown above, so you can check any result by hand. Read how we calculate and check our numbers. Results are estimates for planning: your own prices, equipment and habits will move them.
LED saving per bulb by brightness
Brightness in lumens, the incandescent bulb it replaces and the range of LED watts in the US Department of Energy FEMP table. Saving per bulb per year at the calculator defaults (3 hours a day, 17 cents per kWh).
| Brightness | Old incandescent | LED watts | Saving per bulb per year |
|---|---|---|---|
| 450 lumens | 40 W | 4.5 to 7.0 W | $6.14 to $6.61 |
| 800 lumens | 60 W | 5.9 to 10.5 W | $9.21 to $10.07 |
| 1,100 lumens | 75 W | 9.5 to 14.0 W | $11.36 to $12.19 |
| 1,600 lumens | 100 W | 10.5 to 18.0 W | $15.26 to $16.66 |
Tips before you buy
- Compare lumens, not watts. A 60 W incandescent bulb gives about 800 lumens, and an LED with the same lumens uses a fraction of the watts. The Lighting Facts label on the box gives the lumens, the watts and the yearly energy cost.
- Start with the bulbs that are on longest: kitchen, living room, outdoor and hallway lights. A bulb on 6 hours a day saves twice as much as one on 3 hours.
- Check the box for "dimmable" if the fixture has a dimmer, and for the shape and base (A19 with a standard base is the usual one). A non-dimmable LED on a dimmer flickers or buzzes.
- Halogen and CFL bulbs use less than incandescent ones, so enter their real watts: the saving from a halogen or a CFL is smaller than from an old incandescent bulb.
- A plug-in watt meter shows what an existing lamp really draws, if the old bulb has no label.
Tools & materials for this project
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Frequently asked questions
How much does it cost to run a 60 watt bulb for a year?
At 3 hours a day and 17 cents per kWh, a 60 W bulb uses 65.7 kWh and costs $11.17 a year. A 9 W LED costs $1.68.
How much do LED bulbs save compared to incandescent?
An LED that gives the same light as a 60 W incandescent bulb typically uses 6 to 10 W (the DOE range for 800 lumens is 5.9 to 10.5 W), an energy cut of around 85% at 9 W. The money saved depends on your price per kWh and the hours the bulb is on.
How many lumens is a 60 watt bulb?
About 800 lumens. A 40 W bulb is about 450 lumens, 75 W about 1,100 and 100 W about 1,600.
How long do LED bulbs last?
ENERGY STAR certified LED lamps are required to last at least 10,000 hours, which is about 9 years at 3 hours a day. Many are rated for more.
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Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.