How Much Electricity Does a Incandescent Light Bulb Use?

What an incandescent bulb actually draws

A standard incandescent bulb draws exactly what its label says — 60 W for the common size, with 40 W and 100 W bulbs at the ends of the usual range. Unlike almost every other appliance on this site, there is no gap between nameplate and running wattage. A filament is a resistor: apply mains voltage and it draws its rated power continuously, with no duty cycle, no start-up surge worth mentioning and no idle state.

What the label does not tell you is how little of that becomes light. A 60 W incandescent converts roughly 10 percent of its electricity into visible light and about 90 percent into heat. It is, functionally, a small space heater that happens to glow. This is not a defect in a particular bulb; it is how heating a tungsten filament to incandescence works.

Compared at the same 3 hours a day — the federal standard assumption used on lighting labels — an incandescent uses about 6.7 times the electricity of an LED producing identical brightness.

These bulbs are no longer generally sold. DOE's general service lamp rules effectively ended US sales of most of them in August 2023. But installed bulbs, three-way lamps, appliance bulbs and several exempted specialty types remain in service in millions of homes, which is why the number still matters.

What that costs, worked through

Watts × hours ÷ 1,000 = kWh per day. For one 60 W bulb: 60 × 3 = 180 watt-hours, or 0.18 kWh a day. Over a 30.4-day month that is 5.5 kWh, and at the US average rate of 18.44 cents per kWh, about $1.01 a month. Annually: 65.7 kWh, or roughly $12.11 per bulb.

At the ends of the range, a 40 W bulb costs about 67 cents a month and a 100 W bulb about $1.68. A single 100 W bulb left burning around the clock — a basement or workshop light forgotten for a year — would use 876 kWh and cost about $161.53, which is more than most whole appliances on this site.

Set against the LED equivalent, one bulb saves 55.8 kWh and about $10.29 a year. Ten such fixtures is roughly $103 a year.

And then there is the second bill, the one that never appears in bulb comparisons. In an air-conditioned house, every watt of waste heat is a watt the air conditioner must remove, at roughly a third of a watt of compressor power. A 60 W bulb dumping heat into a cooled room therefore adds about 20 W of cooling load while it burns. Over three hours a day of cooling season that is real extra consumption on top of the bulb's own. Run your own numbers in the appliance energy cost calculator.

What makes the number move

An incandescent bulb is the most predictable electrical device in a house. Its consumption moves for only a few reasons:

• Rated wattage. Directly and exactly. A 100 W bulb costs 2.5 times a 40 W bulb to run, and there is no efficiency spread between brands to complicate it.
• Hours burned. The other half of the multiplication, and the half you control. A porch light on a dusk-to-dawn timer may run 4,000 hours a year against a dining-room fixture's 200.
• Season. Lighting hours rise in winter and fall in summer. Do not annualise a December figure by multiplying by twelve — you will overstate the year substantially. The three-hour standard already averages across seasons.
• Dimming. Genuinely reduces draw, and incandescents dim smoothly on any ordinary dimmer, which is one of the few practical advantages they retain.
• Cooling season. Not a change in the bulb's draw, but a real change in what the bulb costs, through the air-conditioning penalty.

Voltage matters at the margins — a bulb on a slightly high supply voltage runs brighter, hotter and shorter-lived — but not enough to plan around. Nothing about age changes consumption: an incandescent draws its rated wattage on the day it fails just as it did when new, unlike a refrigerator whose seals and compressor degrade.

Whether it is worth doing anything about

Yes. This is one of the few appliances on the site where the recommendation is unambiguous, and the reason is the double billing.

In an air-conditioned house, incandescents are paid for twice: once at the meter for the electricity they consume, and again for the compressor power the air conditioner spends removing the heat they produce. At roughly a third of a watt of cooling per watt of heat, replacing them during cooling season saves noticeably more than the bulb arithmetic alone predicts — the $10.29 a year per bulb is a floor, not a total.

Target correctly. Go after the highest-hour fixtures first: kitchen and porch, not the closet. A bulb burning five hours a day is worth five times one burning an hour, and no amount of good intentions about the linen cupboard changes that. Exterior lights on timers or photocells are usually the single biggest incandescent load left in a house, precisely because nobody watches them.

Two honest caveats. In a heated house in winter, the waste heat is not entirely wasted — it offsets some heating, though electric resistance heat from a light bulb is an expensive way to warm a room and useless in summer. And for genuinely low-hour fixtures, replacing a working bulb proactively saves so little that waiting for it to fail is defensible. Everywhere else, replace them. See why your electric bill is so high for the rest of the audit.

How it compares with everything else you plug in

One 60 W incandescent at 5.5 kWh a month is not a small load by the standards of small devices. It uses nearly seven times what an LED of equal brightness uses at 0.8 kWh, about eleven times a phone charger's 0.5 kWh, slightly less than a WiFi router at 5.8 kWh, and about the same as a vacuum cleaner at 5.0 kWh.

Six of these bulbs together use about 33 kWh a month — roughly a refrigerator's 36.5 kWh, from lighting alone. Ten of them approach an electric dryer at 54.7 kWh. That is how a house full of incandescents used to produce lighting bills that people noticed, and why EIA's 654 kWh a year for all household lighting is described as being down sharply from the incandescent era.

Against the largest loads it remains modest: a central air conditioner at 638.4 kWh a month in cooling season is more than a hundred of these bulbs, and an electric water heater at 232.6 kWh is over forty.

The useful way to hold both facts at once: a single bulb will never explain a surprising bill, but lighting was once a top-five household load and is now, for most homes, a minor one. If yours still is not, the reason is almost certainly a handful of high-hour incandescent or halogen fixtures still burning. The full comparison table is in the appliance directory.

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