Running cost depends on the lamp's power draw, how long you use it and your electricity unit rate. You can estimate it with a simple calculation. The purchase price and the lux figure do not tell you how much electricity the lamp uses.
The calculation
Cost in pounds = watts ÷ 1,000 × hours used × electricity price in pounds per kWh.
For example, a hypothetical 20-watt lamp used for half an hour consumes 0.01 kWh. At an illustrative rate of £0.30 per kWh, that session costs £0.003, or 0.3p. Thirty identical sessions would cost 9p.
The rate here is an example, not a statement of the current UK price cap or your tariff. The wattages below are also examples, not verified DAYARC consumption figures.
Worked examples: 30 minutes per day
- 10 watts: 0.005 kWh per session; 0.15p per session; 4.5p for 30 days.
- 20 watts: 0.01 kWh per session; 0.3p per session; 9p for 30 days.
- 40 watts: 0.02 kWh per session; 0.6p per session; 18p for 30 days.
All three use the same illustrative 30p-per-kWh rate. These calculations cover active use only. They do not include any standby consumption or your household's standing charge.
Where do you find the right numbers?
- Check the manual or manufacturer specification for the lamp's input power or measured consumption.
- Check your electricity bill for the unit rate in pence per kWh.
- Convert your instructed session length into hours: 30 minutes is 0.5 hours.
- Multiply by the number of sessions you expect to use.
An adapter's maximum output rating is not necessarily the lamp's actual power draw. If the only number available is on the adapter, ask the manufacturer for a consumption figure rather than presenting it as a precise running cost.
What else belongs in your budget?
Consider purchase price, delivery, suitable placement and replacement parts alongside electricity. A cheap-to-run device is not a good purchase if it does not fit the required position in your home. Do not shorten or extend a session solely to match the illustrative examples here; follow the lamp's instructions.
See Rise and Mini for current purchase prices, then use our UK buying checklist to compare the practical details.