LED Bulb Savings Calculator
What replacing incandescent or halogen bulbs with LEDs saves in electricity, money and emissions each year — and how quickly the new bulbs pay for themselves.
An LED gives the same light for about a sixth of the power of an incandescent and a quarter of a halogen: a 60 W bulb is replaced by a 9 W LED.
How the led bulb savings calculator works
An LED gives the same light for about a sixth of the power of an incandescent and a quarter of a halogen: a 60 W bulb is replaced by a 9 W LED. Multiply the wattage difference by the hours lit and the number of bulbs for kilowatt-hours saved, then by your tariff for money and by your grid’s emissions factor for CO₂. Payback is the cost of the bulbs divided by the yearly saving.
Formula: kWh saved = (old W − LED W) × hours × bulbs × 365 ÷ 1,000; payback = bulb cost ÷ yearly saving
Worked examples
| Inputs | Saved per year | Note |
|---|---|---|
| Ten 60 W bulbs to 9 W, 4 h a day, 0.32/kWh | 238.27 | 745 kWh, 238 a year |
| Five 50 W halogen downlights to 7 W | 98.09 | 392 kWh, 98 a year |
| One 100 W porch light, 10 h | 50.22 | 314 kWh, 50 a year |
FAQFrequently asked questions
What LED replaces a 60 W bulb?
One rated about 800 lumens — typically 8–10 W. Match lumens, not watts: 450 lm for a 40 W, 800 for 60 W, 1,100 for 75 W, 1,600 for 100 W. Halogen equivalents need about a quarter of the halogen’s wattage.
Should I replace bulbs that still work?
For anything lit an hour or more a day, yes — the electricity saved pays for the LED within months. Bulbs in a rarely used cupboard can wait until they fail.
Do LEDs really last 15,000 hours?
Good ones do, and many are rated 25,000; cheap ones and those in enclosed, hot fittings die sooner. Even at 10,000 hours the saving dwarfs the purchase price.
What grid factor should I use?
Your electricity retailer or national grid operator publishes it. Around 0.2 kg/kWh for a gas-and-renewables grid, 0.4 for a mixed one, 0.7 or more where coal dominates; near zero on 100% renewable plans.
Where these figures come from
- UK DESNZ / DEFRA — Greenhouse gas reporting: conversion factors — the flight, fuel and waste emission factors used here
- Scarborough et al. (2014), Climatic Change — Dietary greenhouse gas emissions — the per-diet daily emission figures
- US EPA — Technical Assistance Document for the Reporting of Daily Air Quality (AQI) — the PM2.5 breakpoints the air quality calculator uses
- US EPA — Greenhouse Gas Equivalencies Calculator — the official US equivalency factors
Last checked: September 2026. Factors are taken from published government and peer-reviewed sources, each named on the page with its year.