LED Savings Calculator Formula

Understand the math behind the led savings calculator. Each variable explained with a worked example.

Use the LED Savings Calculator

Formulas Used

Annual Savings

annual_savings = saved_kwh * rate_per_kwh

Energy Saved per Year

kwh_saved = saved_kwh

CO2 Saved per Year

co2_saved = saved_kwh * 0.92 / 2204.6

Energy Reduction

pct_reduction = (old_wattage - led_wattage) / old_wattage * 100

Variables

VariableDescriptionDefault
num_bulbsNumber of Bulbs to Replace20
old_wattageOld Bulb Wattage(watts)60
led_wattageLED Replacement Wattage(watts)9
hours_per_dayHours Used per Day(hours)5
rate_per_kwhElectricity Rate(USD/kWh)0.15
old_annual_kwhDerived value= num_bulbs * old_wattage * hours_per_day * 365 / 1000calculated
led_annual_kwhDerived value= num_bulbs * led_wattage * hours_per_day * 365 / 1000calculated
saved_kwhDerived value= old_annual_kwh - led_annual_kwhcalculated

How It Works

How to Calculate LED Savings

LEDs use 75-85% less energy than incandescent bulbs and 30-40% less than CFLs while lasting much longer.

Formula

Energy Saved = Bulbs * (Old Watts - LED Watts) * Hours/Day * 365 / 1,000

Cost Saved = Energy Saved * Rate per kWh

Typical Equivalents

  • 60W incandescent = 9W LED
  • 100W incandescent = 15W LED
  • 150W incandescent = 23W LED

    • Worked Example

    Replace 20 incandescent 60W bulbs with 9W LEDs, used 5 hours/day at $0.15/kWh.

    num_bulbs = 20old_wattage = 60led_wattage = 9hours_per_day = 5rate_per_kwh = 0.15
    1. 01Old annual kWh: 20 * 60 * 5 * 365 / 1,000 = 2,190 kWh
    2. 02LED annual kWh: 20 * 9 * 5 * 365 / 1,000 = 328.5 kWh
    3. 03Energy saved: 2,190 - 328.5 = 1,861.5 kWh
    4. 04Annual savings: 1,861.5 * $0.15 = $279.23

    Frequently Asked Questions

    How long do LED bulbs last?

    LED bulbs typically last 25,000-50,000 hours compared to 1,000 hours for incandescents and 8,000-10,000 for CFLs. At 5 hours/day, an LED lasts 13-27 years.

    Are LEDs worth the higher upfront cost?

    Yes. LED bulbs cost $2-5 each and save $5-10 per year per bulb in electricity. They pay for themselves in a few months and last years longer.

    Do LEDs work with dimmer switches?

    Most LEDs are dimmable, but you need to check the label. Dimmable LEDs require compatible dimmer switches designed for LED loads.

    Ready to run the numbers?

    Open LED Savings Calculator