Light Bulb Savings Calculator Formula
Understand the math behind the light bulb savings calculator. Each variable explained with a worked example.
Formulas Used
Annual Savings
annual_savings = (annual_kwh_old - annual_kwh_new) * electricity_rateOld Bulbs Annual Cost
old_annual_cost = annual_kwh_old * electricity_rateLED Annual Cost
new_annual_cost = annual_kwh_new * electricity_rateVariables
| Variable | Description | Default |
|---|---|---|
old_watts | Old Bulb Wattage(W) | 60 |
new_watts | LED Wattage(W) | 9 |
hours_per_day | Hours Used per Day(hours) | 5 |
electricity_rate | Electricity Rate(USD/kWh) | 0.13 |
num_bulbs | Number of Bulbs | 10 |
annual_kwh_old | Derived value= old_watts * hours_per_day * 365 / 1000 * num_bulbs | calculated |
annual_kwh_new | Derived value= new_watts * hours_per_day * 365 / 1000 * num_bulbs | calculated |
How It Works
LED vs Incandescent Energy Savings
LED bulbs use 75-85% less energy than incandescent bulbs while producing the same light output.
Formula
Annual kWh = Wattage x Hours/Day x 365 / 1000 x Number of Bulbs
Annual Savings = (Old kWh - New kWh) x Electricity Rate
A 9W LED replaces a 60W incandescent with equivalent brightness (800 lumens). Over 10 bulbs used 5 hours daily, the savings add up quickly.
Worked Example
Replacing 10 incandescent 60W bulbs with 9W LEDs, used 5 hours/day at $0.13/kWh.
old_watts = 60new_watts = 9hours_per_day = 5electricity_rate = 0.13num_bulbs = 10
- 01Old annual kWh = 60 x 5 x 365 / 1000 x 10 = 1,095 kWh
- 02New annual kWh = 9 x 5 x 365 / 1000 x 10 = 164.25 kWh
- 03Annual savings = (1,095 - 164.25) x $0.13 = $121.10
Ready to run the numbers?
Open Light Bulb Savings Calculator