Running a typical 9-watt LED bulb for 24 hours costs about $0.04 at the U.S. residential electricity rate of roughly $0.17 per kilowatt-hour. The exact cost depends mainly on bulb wattage, your utility rate, and whether the light is on continuously or dimmed.
| Item | Low | Average | High | Notes |
|---|---|---|---|---|
| 9-watt LED for 24 hours | $0.026 | $0.037 | $0.065 | At $0.12, $0.17, and $0.30 per kWh |
| Typical LED wattage | 5 watts | 9 watts | 15 watts | Brightness and design vary |
| Energy used in 24 hours | 0.12 kWh | 0.216 kWh | 0.36 kWh | Based on continuous operation |
What a 24-hour LED bulb run usually costs
A standard LED bulb using 8-10 watts costs about $0.02-$0.07 for a full day across electricity rates of $0.12-$0.30 per kWh. At the national average rate used here, a 9-watt bulb costs about 4 cents per day. These figures cover the electricity consumed by the bulb, not fixed monthly utility fees.
For a quick estimate, multiply watts by 24 hours, divide by 1,000, then multiply by the electricity price per kWh. For example, a 9-watt bulb uses 0.216 kWh in a day; at $0.17 per kWh, that comes to about $0.037. Assumptions: one bulb, 24 hours of use, no dimming, and a residential energy rate excluding fixed fees.
How wattage and utility charges shape the bill
The bulb’s direct energy charge is the main variable in this calculation. A utility bill may also include delivery charges or taxes that vary with usage, but fixed customer charges generally apply whether the bulb is on or off. To make a close estimate, use the total per-kWh rate shown on the bill rather than a rate advertised before delivery fees.
| Cost component | How it applies | Example for a 9-watt bulb | Price range |
|---|---|---|---|
| Energy use | 0.216 kWh over 24 hours | At $0.12-$0.30 per kWh | $0.026-$0.065 |
| Usage-based delivery | Included in some all-in rates | Check the bill’s per-kWh charges | Varies by utility |
| Fixed service fee | Not caused by one bulb | Monthly account charge | Often $5-$25 per month |
| Taxes and surcharges | May scale with usage or bill total | Depends on local rules | Varies by location |
Use the all-in energy rate when comparing the bulb’s added cost, but do not assign the full fixed bill charge to the light.
Why 5-, 9-, and 15-watt bulbs cost different amounts
Wattage directly determines the electricity used when bulbs run for equal hours. At $0.17 per kWh, a 5-watt bulb costs about $0.020 for 24 hours, a 9-watt bulb about $0.037, and a 15-watt bulb about $0.061. A 15-watt model can provide more light, but comparing lumens as well as watts helps show how efficiently each bulb produces brightness.
At the same rate, a 9-watt bulb running continuously for 30 days costs about $1.10; for a full year, it costs about $13.40. A 15-watt bulb would cost about $1.84 monthly and $22.34 yearly. These totals assume 720 hours per month and 8,760 hours per year, with no outage or change in rate.
Every additional watt adds about $0.0041 per 24-hour day at $0.17 per kWh. A 10-watt difference therefore adds roughly $1.24 over 30 days of continuous use.
How local electricity rates change the 24-hour price
Electricity prices vary substantially by state, utility, and plan. At $0.12 per kWh, a 9-watt bulb costs about 2.6 cents per day; at $0.30, it costs about 6.5 cents. Those rates produce monthly costs of about $0.78 and $1.94, respectively, for constant operation.
Time-of-use plans can shift the price when electricity is used during peak periods. A bulb draws little power compared with heating or cooling equipment, so even a large rate difference usually changes its daily cost by only a few cents. The current bill or utility rate schedule is more useful than a national average for a household estimate.
For a personal estimate, substitute the household’s actual per-kWh rate into the wattage formula.
When brightness, dimming, and bulb type affect usage
LED bulbs sold as replacements for 60-watt incandescent lamps commonly use around 8-10 watts, while brighter bulbs may use 12-15 watts or more. Check the package for actual wattage and lumens; the “60-watt equivalent” label describes approximate brightness, not electricity draw. Smart bulbs also use a small amount of standby power when switched off, but the amount varies by model.
Dimming can reduce consumption if the bulb and dimmer are compatible, although the reduction is not always proportional to the dimming percentage. A bulb used at half brightness may not use exactly half its rated watts. For an accurate figure, consult the manufacturer’s wattage data for the dimmed setting.
Rated watts, not incandescent-equivalent watts, determine the base running-cost calculation.
Is leaving one LED on cheaper than replacing it
For electricity alone, continuous operation is inexpensive for a single low-wattage bulb, but it still adds up across multiple fixtures. Ten 9-watt bulbs left on all day cost about $0.37 daily at $0.17 per kWh, or roughly $11 monthly. Turning lights off when they are not needed reduces energy use in proportion to the hours avoided.
LEDs generally last far longer than incandescent bulbs, but rated life depends on the product and operating conditions. Frequent switching is not usually a reason to keep an LED on; check the packaging for rated life and suitability for enclosed fixtures. Heat buildup in a closed fixture can shorten the life of some bulbs.
Ways to lower the cost without changing light quality
Choose a bulb with the required lumens rather than buying extra brightness, and compare actual wattage among products with similar light output. If the bulb stays on for security or accessibility, a timer or smart schedule can reduce unnecessary daytime hours. For example, cutting a 9-watt bulb’s use from 24 to 12 hours halves its energy cost, from about $1.10 to $0.55 monthly at $0.17 per kWh.
When comparing quotes or products, the purchase price is only one part of the expense. For a bulb used continuously, the difference between two efficient models may be just a few dollars in electricity over several years, depending on wattage and local rates. Avoid replacing a working bulb solely for a small theoretical savings unless its wattage or operating hours are high.
The largest practical savings usually come from reducing unnecessary hours or choosing a lower-wattage bulb that still provides enough lumens.