Compare the electricity used by existing bulbs and proposed LEDs, then estimate annual savings, upfront cost, simple payback, and net savings over a selected period. The assumptions remain visible so you can check the result against your own tariff and usage.
How to use this calculator
Enter how many bulbs you will replace, actual watts per existing and new bulb, daily operating hours, and days used per week. Enter your electricity price in currency units per kWh: for example, 15 cents is 0.15 dollars. Add the price per new bulb and, if needed, total installation cost under the projection settings.
The currency selector changes display units only. It does not convert amounts using exchange rates. Keep all prices in the same currency.
Compare similar light output before comparing cost
Use actual electrical wattage, not a package statement such as “60 W equivalent.” Check that the existing and proposed bulbs provide the light output you need. The linked Lumens to Watts Calculator can help interpret a product efficacy rating.
Electricity savings are the difference in energy consumption multiplied by your tariff. Simple payback is the upfront replacement cost divided by those savings. If the proposed bulbs use more electricity, savings can be negative and the calculator does not claim a payback.
The annual estimate reuses the site’s electricity model, which averages 365.25 days per year. Months in the payback result are one twelfth of this modeled year; they are not exact calendar dates.
Examples
Replacing ten bulbs
Ten 60 W bulbs replaced by ten 9 W bulbs, used 3 hours daily throughout the week, save approximately 558.83 kWh per year. At $0.15/kWh, that is $83.82 per year.
Accounting for purchase cost
If each new bulb costs $3 and installation costs nothing, the upfront cost is $30. With the usage above, simple payback is about 4.29 months and five-year net savings are approximately $389.12.
Formula
annual hours = hours per day × days per week × 365.25 / 7
annual kWh saved = bulb count × (old watts − new watts) × annual hours / 1,000
annual cost saved = annual kWh saved × price per kWh
net savings = annual cost saved × years − upfront cost
Interpreting the result
The projection holds usage and tariff constant. It includes the entered initial bulbs and installation, but excludes future bulb replacements, differing lifespans, maintenance, financing, taxes not included in the prices, and effects on heating or cooling demand. With zero electricity savings, there is no energy-cost payback.
An optional CO₂ result uses only the factor you supply in kg CO₂ per kWh. Leave it blank to omit the estimate. A supplier or regional factor should match the place, year, and emissions boundary you want to assess; the tool does not assume one universal grid factor or calculate a product lifecycle footprint.
Sources and method
Virginia Tech: estimating appliance and electronic energy use
The worked examples use this calculator’s stated assumptions.