How much do festoon / string lights cost to run?
About 0.39p an hour in the UK and 0.28¢ an hour in the US. Festoon / string lights draw about 15 W for as long as they are on. Mains festoon lighting still pays the inverter idle penalty — 12 V strings do not.
What they cost, by how long they run
| Running for | kWh | UK | US |
|---|---|---|---|
| 10 minutes | 0.002 | 0.07p | 0.05¢ |
| An hour | 0.015 | 0.39p | 0.28¢ |
| An 8-hour night | 0.12 | 3.2p | 2.2¢ |
| A full day (24 hours) | 0.36 | 9.5p | 6.6¢ |
| A month at 8 hours a day | 3.6 | 95p | 66¢ |
UK prices use the Ofgem price cap for 1 October to 31 December 2026 (direct debit, average across England, Scotland and Wales, with no VAT on electricity this winter): 26.32p per kWh (Ofgem). The standing charge of 54.83p a day is paid whatever you run, so it is left out. US prices use the US average residential price for June 2026 from the Energy Information Administration: 18.34¢ per kWh (EIA). Your own tariff is on your bill; scale the figures by it.
Measure your own
These are typical figures for a typical unit. A plug-in energy monitor between the socket and the appliance shows the real watts and adds up the kWh, so after a day or a week you know exactly what it costs on your tariff.
Compared with similar appliances
| Appliance | Average W | UK per hour | US per hour |
|---|---|---|---|
| LED camping lights | 10 | 0.26p | 0.18¢ |
| Festoon / string lights | 15 | 0.39p | 0.28¢ |
| 12 V compressor cool box (Dometic CFX5, Alpicool) | 18 | 0.47p | 0.33¢ |
| Car fridge (12 V, 40 L) | 18 | 0.47p | 0.33¢ |
| Heated jacket battery | 20 | 0.53p | 0.37¢ |
| Heated blanket, 12 V | 23 | 0.59p | 0.41¢ |
| Thermoelectric cool box | 48 | 1.3p | 0.88¢ |
| E-bike charger | 150 | 3.9p | 2.8¢ |
Running it in a power cut
See which power station will run festoon / string lights, and for how long.
Appliance draw modelled on web.archive.org. The US Department of Energy retired this page in 2025; the link is the Internet Archive's June 2024 capture. The figures remain typical ranges for a typical unit, not a specification.
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