Calculate savings from switching to LED bulbs.
Savings = (old bulb watts − LED watts) × hours/day × days × electricity rate / 1000.
Replacing a 60 W bulb with a 9 W LED used 4 hours/day at $0.15/kWh saves about $11.20/year per bulb.
Divide the LED bulb cost by the annual savings to find how many years until it pays for itself.
It focuses on energy savings; LED lifespans also reduce replacement costs over time.
Use your electricity rate per kWh from your utility bill.