Lighting running costs: watts, operating hours and a comparison worksheet
Lighting energy use is a calculation of power and time. Compare products at a suitable light output and quality, then apply operating hours and your actual electricity tariff.
How is annual lighting electricity use calculated?
Annual electricity in kWh equals watts per lamp multiplied by the number of lamps and annual operating hours, divided by 1,000. The calculation uses the electrical power of the complete equipment being compared. Include separate control gear or standby consumption when relevant rather than silently excluding those loads.
The EU light-source labelling regulation displays consumption per 1,000 operating hours. A household still needs its own operating schedule to turn that label figure into an annual estimate.
| Example input | Existing arrangement | Proposed arrangement |
|---|---|---|
| Lamp count | 10 | 10 |
| Input power per lamp | 8 W | 5 W |
| Annual operating hours | 1,500 | 1,500 |
| Calculated annual use | 120 kWh | 75 kWh |
The calculated difference is 45 kWh per year. The table is an illustrative comparison, not a claim that every 5 W product replaces every 8 W product. Check output, distribution, colour quality and controls before treating two products as alternatives.
How much money does the energy difference represent?
The monetary difference equals the calculated kWh difference multiplied by the variable electricity price that applies to the household or premises. A fixed standing charge normally remains even if the lamps use less electricity. The tariff scenarios below are chosen examples and are not national electricity-price statistics.
| Example variable tariff | Annual difference for 45 kWh |
|---|---|
| EUR 0.20/kWh | EUR 9.00 |
| EUR 0.30/kWh | EUR 13.50 |
| EUR 0.40/kWh | EUR 18.00 |
Where electricity prices vary by time, calculate each operating period separately. Retain whether the entered price includes tax. Comparing a net business tariff with a tax-inclusive household tariff would produce a misleading result.
Why is the energy class not an annual cost prediction?
An energy class describes the regulated efficacy band of a light source, while annual cost depends on the installed quantity, electrical input, hours and tariff. The EPREL label guide explains the adjusted efficacy calculation and the source-type factor used for the class.
Record the exact model identifier and its EPREL entry. Similar packaging or a shared family name does not establish identical power, output or lifetime. A replacement schedule should preserve the product evidence so that a substitution can be checked without reconstructing the original quotation.
What should a lighting quote include besides electricity use?
A lighting quote should separate product purchase, installation, controls and any maintenance assumptions from the operating-energy estimate. The energy worksheet does not assess glare, illumination at the task, electrical compatibility or the cost of access equipment for replacement.
- Match the proposed light output and distribution to the task.
- Confirm the fitting, dimmer and control-gear compatibility.
- Enter a documented operating schedule and tariff.
- Calculate operating energy separately from purchase costs.
- Review the workplace lighting requirements where the installation serves a workplace.
Download the worksheet
The CSV worksheet contains the comparison rows from this page and can be opened in a spreadsheet. Save a dated copy with the source documents, replace illustrative inputs with the project figures, and keep the assumptions visible when sharing a calculation.
Questions and answers
Does a class A lamp guarantee the lowest annual bill?
No. Annual electricity use also depends on input power, the installed quantity and operating hours.
Are the example tariffs market averages?
No. EUR 0.20, 0.30 and 0.40 per kWh are illustrative inputs. Replace them with the applicable tariff.