Every light bulb converts electricity into light β and, wastefully, heat. An old-style incandescent turns only about 10% of its electricity into visible light; the rest becomes heat. That is why a 60 W incandescent and a 9 W LED can produce the same 800 lumens of brightness: the LED simply wastes far less energy as heat.
Typical values from DOE Lighting Facts / industry data. Actual bulbs vary by brand β the calculator lets you override wattage.
How much does it cost to run a light bulb per year?
Multiply the bulb's wattage by the hours it runs per day and 365 days, then divide by 1000 to get kWh per year, and multiply by your electricity rate. Example: a 60 W incandescent bulb running 5 hours a day uses 109.5 kWh per year, which costs $16.43 per year at $0.15 per kWh. An equivalent 9 W LED costs only $2.46 per year.
LED vs incandescent cost calculator: how much can I save switching to LED?
Savings per year equal (old watts minus new watts) times hours per day times 365 divided by 1000 times your rate. Replacing one 60 W incandescent with a 9 W LED at 5 hours per day and $0.15 per kWh saves 93.1 kWh and $13.96 per bulb per year. With 20 bulbs, that is about $279 per year.
How long is the payback period when upgrading to LED bulbs?
Payback equals the extra upfront cost divided by the daily savings. Example: a $5 LED versus a $1 incandescent is a $4 difference, and daily savings of $0.0383 give a payback of about 105 days, roughly 3.5 months. After that, every year of use is pure savings.
How many watts does an LED use to replace a 60 watt incandescent?
Brightness is measured in lumens, not watts. A 60 W incandescent produces about 800 lumens, which equals roughly 43 W halogen, 13 to 14 W CFL, or 8.5 to 9 W LED. Common equivalents: 40 W = 450 lumens, 75 W = 1100 lumens, 100 W = 1600 lumens, 150 W = 2600 lumens.
What is the lifetime cost difference between LED, CFL, halogen, and incandescent?
At 5 hours per day and $0.15 per kWh, one 800-lumen bulb costs per year about $16.43 in energy for incandescent, $11.80 for halogen, $3.83 for CFL, and $2.46 for LED. Adding replacement bulbs, annual ownership is roughly $21.44 for incandescent, $16.35 for halogen, $4.20 for CFL, and $2.83 for LED, because LEDs last about 25,000 hours versus 1,200 hours for incandescent.
How much electricity does a light bulb use per hour?
A bulb rated at W watts uses W divided by 1000 kWh per hour. A 60 W bulb uses 0.06 kWh per hour, a 9 W LED uses 0.009 kWh per hour. Multiply by your rate to get the hourly cost: at $0.15 per kWh, the 60 W bulb costs $0.009 per hour.
How much does it cost to leave a light on all day (24 hours)?
A 60 W bulb left on 24 hours uses 1.44 kWh per day, costing $0.216 per day or about $78.84 per year at $0.15 per kWh. A 9 W LED left on 24 hours costs only about $11.83 per year.
How do I calculate lighting cost for a whole house with multiple rooms?
For each room, compute watts times hours per day times 365 divided by 1000 times the number of bulbs, then sum all rooms and multiply by your rate. The Whole Home tab of this calculator does this automatically, including a CO2 estimate.
How does a tiered (block) electricity tariff affect lighting cost?
With tiered tariffs, each block of monthly kWh is priced differently, so lighting added on top of other usage may fall into an expensive tier. This calculator lets you define up to three tiers and computes the exact bill for your lighting kWh, plus the effective average rate.
How much CO2 does lighting produce?
Multiply lighting kWh by your grid emission factor. The default is 0.7 kg CO2 per kWh and is editable. A 60 W bulb at 5 hours per day produces about 76.7 kg of CO2 per year, while the equivalent LED produces about 11.5 kg.
Do dimmers, smart bulbs, and standby power change the calculation?
Yes. A dimmed bulb uses roughly proportional power to its dim level, so 50 percent dimming saves close to 50 percent of energy. Smart bulbs draw a small standby load, typically 0.2 to 1 W, even when off. For a full appliance-level breakdown including standby loads, see our appliance energy calculator.
What is the formula for lighting energy cost?
Energy (kWh) = watts times hours per day times days per year divided by 1000. Cost = energy times electricity rate in dollars per kWh. Annual savings from an upgrade = (old watts minus new watts) times hours per day times 365 divided by 1000 times rate times number of bulbs.
Is this lighting calculator different from a generic energy cost calculator?
Yes. This tool is built specifically for lighting: equal-brightness (lumens) comparison across incandescent, halogen, CFL, and LED, bulb lifetime and replacement costs, multi-room whole-home totals, and tiered tariffs. For any other device, use our generic energy cost calculator or the appliance energy calculator with its 62-device database.
Can I use this calculator for commercial or office lighting?
Yes. Enter the total number of fixtures, their wattage, and operating hours per day (for example 10 to 12 hours for offices). The whole-home tab works the same for offices, shops, or warehouses, and the comparison table shows the business case for an LED retrofit including payback time.