An LED bulb uses roughly a tenth of the electricity of the old incandescent it replaced, and about half of a halogen, for the same amount of light in the room. Change a 60-watt bulb for an LED that looks just as bright and you go from about 60 watts down to around 8. Lighting was never the biggest slice of a home's electricity bill, and LEDs have shrunk it further, but the swap is so cheap and so complete that it is one of the few upgrades that simply pays and then keeps paying. Here is what it is really worth, and the handful of things that trip people up at the shop.
The short answer. An old 60W incandescent bulb, on for three hours a day, costs about £17 a year at an example rate of 26p per kWh. The LED that gives the same light, drawing around 8W, costs a little over £2. That is roughly £15 a year saved on each of your most-used bulbs, for a bulb that costs a pound or two and lasts for years. You fit it once and forget it.
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What an LED actually costs to run
Work through one bulb and the rest becomes obvious. Electricity is billed per kilowatt hour, the unit explained in what is a kWh, and the sum is always power in kilowatts times hours times the unit rate. A 60W incandescent bulb on for three hours a day uses 0.06kW times 3 hours, so 0.18 kWh a day, about 65 kWh across a year, which comes to roughly £17 at an example 26p per kWh. Swap it for an 8W LED that puts out the same brightness and it uses 0.024 kWh a day, under 9 kWh a year, a shade over £2. Do that across the few lights you genuinely leave on for hours, say the kitchen, the living room and the hall, and the saving lands in the tens of pounds a year for almost no outlay. The appliance running cost calculator will run the same figures for your own bulbs and hours.
| Bulb type | Power for the same light | Cost a year at 3h/day |
|---|---|---|
| Incandescent | ~60W | ~£17 |
| Halogen | ~42W | ~£12 |
| CFL (curly bulb) | ~14W | ~£4 |
| LED | ~8W | ~£2.30 |
Illustrative, for a bulb as bright as an old 60W (about 800 lumens), on three hours a day, at an example 26p per kWh. Your own rate and hours will shift the numbers, but the ranking does not change.
Why LED won, and what it replaced
Three generations of bulb sat on the shelf before LED took over. The incandescent bulb, the classic glowing filament, wasted about 90 per cent of its energy as heat and gave only a tenth back as light, which is why it ran so hot and cost so much to leave on. The halogen was a tidied-up incandescent, a little more efficient but not by much. Then came the CFL, the curly energy-saving bulb, which cut the power sharply but annoyed people: it was slow to reach full brightness on a cold morning, it dimmed badly, and it held a trace of mercury. LED fixed the lot. It lights instantly, runs cool, dims well in its dimmable versions, contains no mercury and lasts far longer. Incandescent and most halogen bulbs are no longer sold new in the UK, so for nearly every fitting the LED is now simply what you buy.
Buy by lumens, not by watts
The old habit was to pick a bulb by its wattage, a 60-watt or a 100-watt. That no longer works, because watts measure the power a bulb draws, not the light it gives, and an LED draws so little that the number tells you nothing about brightness. The figure to read is the lumens, which measure light output. As a rough guide, an old 40W bulb gave about 470 lumens, a 60W about 800, and a 100W around 1,500. So if you want a bulb as bright as the old 60W, look for roughly 800 lumens, and it will draw somewhere around 7 to 9 watts. It is also worth glancing at the efficacy, the lumens per watt: a decent LED manages 90 to 120, and a higher figure means more light for less power. The packaging carries this on the energy label, and the new A-to-G rating is explained in energy labels explained.
Warm or cool: getting the colour right
The other number on the box is the colour temperature in kelvin, and buying the wrong one is the most common LED regret. Around 2700K gives a warm white close to the cosy glow of the old incandescent, which suits living rooms and bedrooms. Something near 3000K is a touch crisper. Move up to 4000K and you get a cool, neutral white that works well in kitchens, bathrooms and anywhere you want to see clearly, while 6000K is a bluish daylight better kept to the garage or a security light. A living room fitted with cool white bulbs feels like an office, so match the room to the number. If colour accuracy matters, in a kitchen or where you get dressed, check the colour rendering index too: 80 and above is fine, 90 and above is better.
Dimming, spotlights and the fittings that catch people out
A few practical snags are worth knowing before you buy a boxful. Not every LED dims, so if a bulb sits on a dimmer switch, look for one marked dimmable, and ideally fit a trailing-edge dimmer designed for LEDs; an old dimmer built for incandescent bulbs often causes flicker or a faint buzz. Kitchen spotlights are the other big one: a bank of six or eight 50W halogen GU10 spots is a genuine drain, and swapping each for a 4 or 5 watt LED GU10 is one of the better returns in the house. Check the fitting type before you go, whether it is bayonet, screw, GU10 or one of the small pin fittings, and take the old bulb along to match it. One last thing: if a bulb sits in a fully enclosed fitting, buy one rated for enclosed use, because trapped heat is what shortens an LED's life more than anything else.
Do they really last as long as the box claims?
LED bulbs are sold with rated lives of anywhere from 15,000 to 50,000 hours. At three hours a day, even 25,000 hours is over twenty years, which is why the marketing leans on longevity. In real homes the light-emitting part rarely fails; what gives out first is the small driver circuit inside the bulb, or the bulb cooks itself in a hot, enclosed fitting. That is the difference between a bulb that lasts a decade and a bargain-bin one that flickers and dies in eighteen months. You do not need to spend a fortune, but the very cheapest bulbs in warm fittings can be a false economy. A mid-priced bulb from a name you recognise, in an open fitting, will genuinely go the distance.
Is it worth swapping before the old bulb dies?
For the lights you use most, yes, and there is no need to wait. Any halogen or incandescent bulb still in daily use is quietly costing you money every hour it burns, so on a heavily used kitchen or living-room fitting a new LED pays for itself within months. The bulbs to leave alone are the ones barely used, a cupboard light on for two minutes a day or the bulb in the spare room, where the saving is pennies and there is no sense binning a working bulb. Sort the house by hours, not by the count of bulbs: change the ones that are on for hours first, and let the rest live out their days.
Where lighting really sits in the bill
Worth a reality check before you expect miracles. Even in the incandescent era, lighting was only about 10 to 15 per cent of a home's electricity, and with LED it is often under 5. So switching every bulb is well worth doing, because it is cheap, permanent and needs no thought once done, but it will not transform your bill on its own. The money in a home's electricity is made by the things that make heat: the electric shower, the kettle, the tumble dryer and the oven. Lighting is a tidy, set-and-forget win rather than the main event. For the fuller picture of where the electricity actually goes, the running cost of every appliance lays it out, and energy saving myths takes apart the old idea that leaving a light on is what drives your bill.
Common questions
How much does an LED bulb cost to run?
About £2 to £3 a year for a typical bulb on three hours a day, at an example rate of 26p per kWh. An 8W LED uses under 9 kWh across a year, against roughly 65 kWh for the old 60W incandescent it replaces, so it costs around a seventh as much to run for the same light.
How much do LED bulbs save compared with old bulbs?
Roughly £15 a year per bulb against an incandescent, and about £10 against a halogen, on a light used three hours a day. Across the handful of fittings you leave on for hours, the total lands in the tens of pounds a year for a few pounds of bulbs.
What LED do I buy to replace a 60W bulb?
Look for around 800 lumens, which is the brightness of an old 60W bulb. That will be an LED of roughly 7 to 9 watts. Buy by the lumens, not the wattage, and pick a colour temperature near 2700K for a warm living-room light or nearer 4000K for a bright kitchen.
Do LED bulbs really last for years?
Good ones do. Rated lives run from 15,000 to 50,000 hours, which is well over a decade at normal use. What shortens them is heat, so a bulb in a sealed fitting needs to be rated for enclosed use, and the very cheapest bulbs are more likely to fail early.