Estimate yearly and monthly savings from switching bulbs to LEDs, with an optional lumen check to avoid a dimmer replacement.
Advanced options
Table of contents
How to use our LED Bulb Replacement Calculator
- Enter Current bulb power and LED bulb power in watts for one bulb of each type.
- Enter Number of bulbs, Use time in hours per day, and Electricity price in $ per kWh from your electric bill.
- Open Advanced options if you know the package lumens, then enter Current bulb brightness and LED bulb brightness to check whether the LED is dimmer.
- Select Calculate and read Estimated yearly electricity bill savings first; a negative value means the LED setup costs more to run.
- Sanity-check the results by making sure Use time is between 0 and 24, the watts are for one bulb, and the brightness warning matches the lumen numbers you entered.
Definitions
Watt: A unit of electric power. In this calculator, Current bulb power and LED bulb power are the watts used by one bulb.
Kilowatt-hour (kWh): A unit of electricity use. One kWh equals 1000 watt-hours.
Electricity price: The cost for one kWh of electricity, entered as dollars per kWh. For example, 16 cents per kWh is entered as 0.16.
Lumen: A brightness rating printed on many bulb packages. Lumens are better than watts for comparing how bright two bulbs are.
Brightness match percent: The LED bulb brightness divided by the current bulb brightness, multiplied by 100. A value below 100% means the entered LED lumens are lower.
Brightness gap: LED bulb brightness minus current bulb brightness, in lumens. A negative gap means the LED is dimmer based on the numbers entered.
Common mistakes and quick fixes
Mistake: Entering total fixture watts in Current bulb power instead of watts for one bulb.
Fix: Use the watt rating for one current bulb, then put the quantity in Number of bulbs.
Mistake: Typing cents into Electricity price as 16 instead of $0.16 per kWh.
Fix: If your bill says 16 cents per kWh, enter 0.16 in Electricity price.
Mistake: Using weekly hours in Use time.
Fix: Convert weekly use to an average day; 21 hours per week becomes 3 hours per day.
Mistake: Leaving Current bulb brightness filled in but leaving LED bulb brightness blank.
Fix: Enter both Current bulb brightness and LED bulb brightness, or leave both blank if you only want a watt-based savings estimate.
Mistake: Ignoring a negative Brightness gap from entered lumens because the dollar savings look good.
Fix: Check the package lumens before buying; a negative Brightness gap from entered lumens means the LED is listed as dimmer.
Limitations & Key Assumptions / Boundary Conditions
- The calculator estimates electricity running cost only. It does not include bulb purchase price, rebates, sales tax, labor, disposal, dimmers, or fixture changes.
- It assumes the old bulbs and LED bulbs are used for the same Number of bulbs and the same Use time every day.
- It uses 365 days per year and divides yearly savings by 12 for the monthly estimate, so it does not model seasonal use or exact billing cycles.
- Electricity price is treated as one flat $ per kWh rate. Tiered rates, time-of-use rates, fixed monthly fees, and taxes can make real bills differ.
- The brightness check uses only the Current bulb brightness and LED bulb brightness values you enter. It does not judge color temperature, beam angle, dimmer compatibility, or room layout.
- A negative Estimated yearly electricity bill savings is allowed. It means the LED bulb power you entered uses more electricity than the current bulb setup.
Methodology
Energy use
The calculator first estimates yearly electricity use for the current bulbs and the LED bulbs. Watts are multiplied by bulb count and daily use time, then converted from watt-hours to kilowatt-hours.
old_kwh_year = old_watts * bulb_count * hours_per_day * 365 / 1000
led_kwh_year = led_watts * bulb_count * hours_per_day * 365 / 1000
Savings
Yearly electricity saved is the current yearly kWh minus the LED yearly kWh. Dollar savings are found by multiplying saved kWh by Electricity price.
annual_kwh_saved = old_kwh_year - led_kwh_year
annual_cost_savings = annual_kwh_saved * electricity_rate
monthly_cost_savings = annual_cost_savings / 12
Brightness check
If both lumen fields are entered, the calculator compares listed brightness. The warning appears when LED bulb brightness is lower than Current bulb brightness.
brightness_match_percent = 100 * led_lumens / old_lumens
brightness_gap_lumens = led_lumens - old_lumens
Worked example
For 10 current bulbs at 60 watts each, 10 LED bulbs at 9 watts each, 3 hours per day, and an Electricity price of $0.16 per kWh, the current bulbs use 657.00 kWh per year and the LED bulbs use 98.55 kWh per year.
annual_kwh_saved = 657.00 - 98.55 = 558.45 kWh per year
annual_cost_savings = 558.45 * 0.16 = $89.35 per year
monthly_cost_savings = 89.35 / 12 = $7.45 per month
If both bulbs are entered as 800 lumens, the brightness match is 100% and the brightness gap is 0 lumens.