How Much Does It Cost to Leave a Light On All Night?
An LED bulb left on for eight hours costs about 2p. An old incandescent costs around 12p. The habit that matters is not the landing light, it is the heating and the appliances.
In short
A 10-watt LED bulb running for eight hours uses 0.08 kWh, about 2p at a 25p unit rate, or around 7 a year if left on every night. An old 60-watt incandescent bulb costs six times as much, roughly 12p a night. Lighting is a small share of most electricity bills; heating, hot water, the tumble dryer and the fridge dominate.
The landing light left on overnight is one of the classic household arguments, and the numbers say it was never worth arguing about. Since LEDs replaced incandescent bulbs the cost has fallen by roughly 85 percent, and it was small before.
The arithmetic
Cost equals wattage divided by 1,000, times hours, times your unit rate.
A 10-watt LED for eight hours: 10 ÷ 1,000 × 8 = 0.08 kWh. At 25p per kWh, that is 2p.
Every night for a year: about 7.
By bulb type
| Bulb | Typical wattage | Cost per 8 hours | Per year, nightly |
|---|---|---|---|
| LED | 8 to 10 W | 2p | 6 to 7 |
| Compact fluorescent | 12 to 15 W | 3p | 9 to 11 |
| Halogen | 40 to 50 W | 9p | 30 to 37 |
| Incandescent | 60 W | 12p | 44 |
If you still have incandescent or halogen bulbs anywhere, replacing them with LEDs is the single best return in the house: a 3 bulb saves 35 a year in the example above and lasts ten times as long.
Where the electricity actually goes
Lighting is typically 5 to 10 percent of a household’s electricity use, and in an LED-lit home it is at the low end. The large items are:
- Electric heating and hot water, if you have them, by a wide margin.
- Tumble dryer, at 2 to 4 kWh a load.
- Electric oven and hob, around 1 to 2 kWh per hour of cooking.
- Fridge-freezer, roughly 1 kWh a day, continuously.
- Washing machine and dishwasher, about 1 kWh a cycle.
A single tumble dryer load costs as much as a month of leaving one LED on all night. If the goal is a smaller bill, the dryer, the thermostat and the standing charges are where the money is. The lights are where the guilt is.
Standby is the quieter cost
A television, games console, set-top box, printer and a few chargers left on standby can draw 20 to 40 watts continuously between them. That is 0.5 to 1 kWh a day, around 45 to 90 a year, for nothing. It is worth more attention than any light switch.
Motion sensors and timers
For outside lights, landings and bathrooms, a sensor or timer removes the question entirely. For a security light the cost of running it all night is around 3p; a sensor version costs less and is a better deterrent, since the light coming on is the signal.
The honest conclusion
Turn lights off when you leave a room because it is a reasonable habit, not because it is saving much. Then go and look at the dryer.
Common questions
Is it cheaper to leave LED lights on than switch them off?
No. That was partly true of old fluorescent tubes, which took extra power to start, but LEDs use nothing when off and cost nothing to switch. Turning them off always saves money, even for a minute.
How much does a whole house of lights cost?
A home with fifteen LED bulbs used an average of four hours a day each uses about 0.6 kWh daily, roughly 15p, or around 55 a year. With incandescent bulbs the same usage would cost over 300.
Do smart bulbs use power when off?
A little, typically 0.3 to 0.5 watts on standby to stay connected. That is around 1p a week per bulb, negligible for one, noticeable across a house full of them.
Sources
Every factual claim above traces to one of these. Follow them rather than taking this article's word for it.
- Energy price cap Ofgem
Try it yourself
Free, instant, and nothing you enter leaves your browser.