Power factor for lamps
According to BRE’s The essential guide to retail lighting:
The term ‘power factor’ is ‘…A measure of the phase difference between the voltage and current in an alternating current (AC) supply. For lamp types other than incandescent, the voltage and current waveforms are not exactly in phase with one another: thus the volts multiplied by the amperes in the circuit may be higher than the Watts. In such cases, the Watts represent the active power, and the volts multiplied by the amperes represent the apparent power. The power factor is the ratio of the absolute value of the active power to the apparent power. Ideally, the power factor should be as close to unity as possible. A low value of the power factor increases the current load and the energy consumption. Most high-wattage lamp circuits are designed to have a power factor greater than 0.85.’
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
- Ballast or control gear.
- Colour appearance.
- Daylight benefits in healthcare buildings.
- Daylight factor.
- Daylight lighting systems.
- Dichroic reflector.
- Discharge lamp.
- Extra-low voltage lamps.
- General lighting v task lighting.
- Illuminance.
- Lamp.
- Lamp efficacy.
- Light pollution.
- Lighting.
- Lighting energy numeric indicator LENI.
- Lighting of construction sites.
- Luminaire efficacy.
- Rights to light.
- The Future of Electricity in Domestic Buildings.
- The UK’s low-carbon future is increasingly electric.
Featured articles and news
The history of building regulations
A story of belated action in response to crisis.
Moisture, fire safety and emerging trends in living walls
How wet is your wall?
Current policy explained and newly published consultation by the UK and Welsh Governments.
British architecture 1919–39. Book review.
Conservation of listed prefabs in Moseley.
Energy industry calls for urgent reform.
Heritage staff wellbeing at work survey.
A five minute introduction.
50th Golden anniversary ECA Edmundson apprentice award
Showcasing the very best electrotechnical and engineering services for half a century.
Welsh government consults on HRBs and reg changes
Seeking feedback on a new regulatory regime and a broad range of issues.
CIOB Client Guide (2nd edition) March 2025
Free download covering statutory dutyholder roles under the Building Safety Act and much more.
AI and automation in 3D modelling and spatial design
Can almost half of design development tasks be automated?
Minister quizzed, as responsibility transfers to MHCLG and BSR publishes new building control guidance.
UK environmental regulations reform 2025
Amid wider new approaches to ensure regulators and regulation support growth.
The maintenance challenge of tenements.
BSRIA Statutory Compliance Inspection Checklist
BG80/2025 now significantly updated to include requirements related to important changes in legislation.