What this calculator does
LED bulb savings works out electricity and replacement-bulb savings from switching to LED lighting. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaAnnual cost = (watts/1000) × hours/day × 365.25 × price/kWh + bulb price × (hours/day × 365.25 / bulb life)
The inputs explained
| Field | What to enter |
|---|---|
| Old bulb wattage (W) | A number, measured in W. Starts at 60. |
| LED wattage (W) | A number, measured in W. Starts at 9. |
| Hours used per day | A number. Starts at 5. |
| Electricity price ($/kWh) | A number, measured in your currency/kWh. Starts at 0.16. |
| Old bulb price ($) | A number, measured in your currency. Starts at 1. |
| Old bulb lifetime (hours) | A number, measured in hours. Starts at 1000. |
| LED bulb price ($) | A number, measured in your currency. Starts at 4. |
| LED lifetime (hours) | A number, measured in hours. Starts at 15000. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with old bulb wattage
Every other input is held at the calculator’s starting values while old bulb wattage varies. Select any row to load that scenario into the calculator.