Replacing a 60 W lamp with a 10 W lamp: estimate the monthly energy difference
Compare power under the same operating hours to isolate the energy effect. Purchase cost and equivalent lighting performance remain separate considerations.
Electricity cost calculator →Calculate matched operating conditions
At five hours daily for thirty days, a 60 W lamp uses 0.06 × 5 × 30 = 9 kWh. A 10 W lamp uses 1.5 kWh. The difference is 7.5 kWh, worth 1.5 currency units at a price of 0.2 per kWh. These figures depend on the stated hours and price, not on a universal monthly saving.
Scale the scenario and examine payback
For eight lamps with identical use, the monthly cost difference becomes twelve. If the additional replacement cost is forty-eight, the simple payback under this unchanged scenario is four months. That calculation excludes the time value of money, lifespan differences and future price changes. It is an illustrative payback, not a promise of when a purchase will repay itself.
Make sure the service is comparable
Brightness, operating time and equipment condition should be comparable before interpreting the difference as a practical saving. If the replacement runs for longer, the saving may shrink. The percentage-change tool can describe the energy reduction, while ROI can organize costs and benefits for a clearly specified period. Neither automatically supplies a suitable tariff or verifies that the replacement provides the required lighting performance.
Try the calculators
- Electricity cost calculator
Estimate energy use and cost from power, usage time and electricity price.
- Percentage change
Measure the change between two values.
- Return on investment calculator
Calculate net gain and ROI from cost, final value, income and expenses.