Combine lower lighting wattage with shorter hours
A family compares a 300 W bank of lights left on for five hours with a 60 W replacement bank used for three hours. Both changes are planned together.
Open CalculatorInputs and calculation
| Tool input | Value |
|---|---|
| Currency | USD |
| Power unit | W |
| Power | 300 |
| Hours per day | 5 |
| Days or equivalent sessions | 30 |
| Duty cycle (%) | 100 |
| Energy price (USD per input kWh) | 0.25 |
| Alternative power (W) | 60 |
| Alternative hours per day | 3 |
| Alternative duty cycle (%) | 100 |
Baseline: 300 ÷ 1,000 × 5 × 30 × 100% = 45 kWh. Alternative: 60 ÷ 1,000 × 3 × 30 × 100% = 5.4 kWh. Multiply both by 0.25; the baseline minus the alternative is USD 9.90.
Modeled difference · USD 9.90
What the comparison shows
Changing wattage alone would take usage from 45 to 9 kWh. The shorter schedule then avoids another 3.6 kWh. Adding two separate estimates from the original baseline would double count part of the reduction.
Assumptions and limits
Keep the number of days and rate fixed. The result covers lamps sharing the same schedule and excludes installation costs.