The short answer (rate checked 28 October 2026)
- A typical 6W LED tree set costs under 1p an evening and about 35p for the whole season, 1 December to 6 January at six hours a night, on the 26.32p per kWh electricity cap.
- The biggest 1,000-light sets that state a wattage claim 25W to 30W. That is about 4p to 5p an evening and £1.46 to £1.75 a season.
- Battery fairy lights are the expensive way to light anything. One 20-light string, on its own stated battery life, costs about 7.4p an hour in coin cells. A 6W mains tree set costs 0.16p an hour, about 47 times less.
- The audit finding: half of the first 20 unsponsored Amazon UK tree-light listings state no wattage at all. One states two, 6W in its specification table and 50W in its description. None of the first 12 outdoor inflatables says how much power its blower uses.
Every December the same question comes round: are the Christmas lights quietly running up the bill? For mains LED lights the answer is almost always no. The more useful questions are which lights cost real money, and why so many listings make it hard to tell.
Prices and specs last checked by Look Into on 28 October 2026 · next check 26 November 2026 · how we picked
The sum, and the rate behind it
Running cost is the wattage times the hours, divided by 1,000 to get kilowatt hours, times the price of a kilowatt hour. We use the Ofgem price cap for 1 October to 31 December 2026: 26.32p per kWh for electricity, paid by direct debit and including VAT. We leave out the daily standing charge, because you pay that whether the lights are on or not.
For the season we use the same yardstick as our outdoor Christmas lights guide. That is 1 December to 6 January, 37 nights, six hours a night, or 222 hours. Six of those nights fall under the January 2027 cap, which Ofgem announces on 25 November. We will rebase this page then. Until then every season figure uses the October rate. Our January 2027 price cap page tracks the announcement.
| Stated wattage | Typical set | Per six-hour evening | Per season (222 hours) |
|---|---|---|---|
| 6W | 200 to 480 LED tree set | 0.95p | 35p |
| 9W | 120 LED 15m plug-in string | 1.42p | 53p |
| 12W | Smart animated tree set | 1.90p | 70p |
| 25W | 1,000 LED multi-function set | 3.95p | £1.46 |
| 30W | 1,000 LED tree set | 4.74p | £1.75 |
| 50W | The higher of one listing's two figures | 7.90p | £2.92 |
To put the top of that table in context, a 2kW fan heater costs 52.6p for a single hour at the same rate. A whole season of a 30W tree set costs about the same as three and a half hours of that heater.
What 20 listings tell you about wattage
We read the first 20 unsponsored Amazon UK results for "christmas tree lights" on 28 October 2026. We checked the title, the About this item bullets, the description, the product overview and the specification tables for a stated power draw.
- 10 of 20 state a wattage.
- 10 of 20 state none, including sets with 400 and 1,000 lights.
- Stated figures run from 6W to 30W, and two sets with 1,000 lights from the same brand state 6W and 25W.
- One 500-light set states 6W in its specification table and 50W in its description, so its running cost is either 35p or £2.92 a season depending on which line you believe.
We also read the first 12 unsponsored results for "christmas inflatable outdoor" the same day. None states the wattage of the fan that keeps it inflated, even though it runs the whole time the inflatable is up. Without that figure nobody can tell you what an inflatable costs to run, and we have not guessed.
If a listing gives no wattage, look on the plug-in transformer itself. Most carry an output rating in volts and amps, and volts times amps gives you an upper limit in watts. An energy-monitoring smart plug will measure the real draw. Our smart plugs guide covers which ones report power use.
Battery lights cost far more than mains
Battery fairy lights look like the cheap option, because the set itself costs very little. The batteries are where the money goes. Of the first 20 unsponsored Amazon UK results for "battery fairy lights", read on 28 October 2026, only two state how long a set of batteries lasts. The others list LED lifetimes of thousands of hours, which tells you nothing about the cells.
One of the two gives enough to work with. A 20-light Jsdoin string runs on two CR2032 coin cells and claims "up to 30 hours" of constant light. Our batteries guide priced Duracell CR2032 cells at £1.11 each on 22 September 2026. Two cells for 30 hours is £2.22 over 30 hours, or 7.4p an hour. That is 44p for a six-hour evening and about £16.43 if you ran it for the full 222-hour season. A 6W mains tree set with ten to twenty times as many lights costs 0.16p an hour, about 47 times less.
Most battery strings run on three AA cells and state no battery life, so we cannot price them the same way. Use them where there is no socket, on a timer, and with rechargeable cells if you use them every night.
A whole house, priced
Add up a common setup: a 6W tree set indoors, a 7.2W connectable rope light along the front of the house and a 9W string in a front window. That is 22.2W in total, which costs about £1.30 for the whole season at six hours a night. The outdoor figures come from our outdoor lights guide, which prices each set on the same 222-hour yardstick.
Hours matter more than lights. Leave that 6W tree set on around the clock from 1 December to 6 January and it costs about £1.40 instead of 35p. A plug-in timer or a smart plug pays for itself on a large display, though it does little on a single LED tree.
Questions people ask
How much does it cost to run Christmas lights for a night?
For a 6W LED tree set, 0.95p for six hours at the 26.32p per kWh October to December 2026 cap. A 30W 1,000-light set costs 4.74p for the same six hours.
Do LED Christmas lights use much electricity?
No. The mains LED sets we found that state a wattage draw 6W to 30W. A whole season of six hours a night costs 35p to £1.75 per set at the current cap.
Are battery fairy lights cheaper to run?
No, they are far dearer. One 20-light coin cell string works out at about 7.4p an hour on its own stated battery life, against 0.16p an hour for a 6W mains tree set.
How much does an outdoor inflatable cost to run?
We cannot say, and neither can the listings. None of the first 12 we read states the wattage of its blower. Check the rating on the fan unit or plug, or measure it with an energy-monitoring plug, then use the sum on this page.
Related reading
- Best outdoor Christmas lights UK 2026
- Best smart plugs UK 2026
- Appliance running cost calculator
- UK Always-On Load Index 2026
Sources
- Look Into, Energy price cap October 2026, Ofgem's 1 October to 31 December 2026 rates: electricity 26.32p per kWh.
- Amazon.co.uk search results for "christmas tree lights" (first 20 unsponsored), "battery fairy lights" (first 20 unsponsored) and "christmas inflatable outdoor" (first 12 unsponsored), with each product page read on 28 October 2026.
- Look Into, Best batteries UK 2026, Duracell CR2032 at £1.11 a cell, read 22 September 2026.
This page carries no affiliate links. It recommends no product, and the listings above are named only as evidence.