Lighting Energy Cost Calculator
Calculate how much your lighting costs per day, month, and year based on wattage, daily usage, and your electricity rate.
Formulas Used
Total Power (kW) = (Wattage per Bulb × Number of Bulbs) ÷ 1,000
Daily Energy (kWh) = Total Power (kW) × Hours Used per Day
Daily Cost ($) = Daily Energy (kWh) × Electricity Rate ($/kWh)
Monthly Cost ($) = Daily Cost × 30.4375 (= 365.25 ÷ 12)
Annual Cost ($) = Daily Cost × 365.25
Annual Energy (kWh) = Daily Energy × 365.25
Assumptions & References
- A month is taken as the average calendar month: 365.25 ÷ 12 ≈ 30.4375 days.
- A year is taken as 365.25 days to account for leap years.
- The default electricity rate of $0.13/kWh is the approximate U.S. residential average (U.S. EIA, 2024).
- The LED vs. incandescent savings estimate uses a 4:1 wattage equivalence ratio (e.g., a 10 W LED ≈ 40 W incandescent), consistent with U.S. DOE guidance.
- Costs shown are for electricity only; bulb purchase price and lifespan are not included.
- The calculator assumes constant daily usage throughout the year.