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

    Ready to run the numbers?

    Open LED Savings Calculator