Illuminance
According to BRE’s The essential guide to retail lighting:
Illuminance is ‘The level of light on a surface; measured in lux (lx). Previously called the illumination value. It can be used as a reference measurement of the performance of a lighting system as related to the activity.'
It is measured in lux (lx), the ‘...SI unit (the International System of Units) of illuminance or amount of light on a surface. One lux is equal to one lumen per square metre (lm/m^2)’ where a lumen (lm) is the ‘...SI unit of luminous flux, describing the quantity of light emitted by a lamp or received at a surface.’
Average illuminance is ‘The illuminance averaged over a specific area. In practice, this may be derived either from an average of the illuminances at a representative number fo points on the surface, or from the total luminous flux falling on the surface divided by the total area of the surface’
Maintained illuminance is ‘Illuminance at the time when maintenance is expected to take place. Most values of illuminance that are quoted as applicable to a store, eg 500-1000 lx, refer to this value. The time taken to reach the maintained illuminance level would depend on the lamp types and application’.
[edit] Related articles on Designing Buildings
- Ballast or control gear.
- Colour appearance.
- Colour Rendering Index CRI.
- Commercial lighting.
- Daylight benefits in healthcare buildings.
- Daylight factor.
- Daylight lighting systems.
- Dichroic reflector.
- Discharge lamp.
- Extra-low voltage lamps.
- General lighting v task lighting.
- Lamps.
- Lamp efficacy.
- Light pollution.
- Lighting.
- Lighting designer.
- Lighting energy numeric indicator LENI.
- Lighting of construction sites.
- Luminaire efficacy.
- Lux.
- Rights to light.
- Uniformity of illuminance.
Featured articles and news
We're expanding our collaborative mission by launching DB Intelligence, an exclusive market research advisory panel. Built environment professionals can now get paid to share their expertise on industry trends, products and services.
Panel members receive direct financial incentives for participating in research projects like short surveys, 1-2-1 interviews and focus groups. Register today to shape the future of the construction sector.
Planning condition discharge in England and Wales
A brief exoplanation from a building compliance expert, with further links.
Overheating guidance and tools for building designers
Guidance for dealing with element of building fabric control that have increasing importance.
Shading for housing, a design guide
From the Good Homes Alliance and British Blind and Shutter Association.
UK Standard Skills Classification (SSC)
A shared framework for describing skills needs.
Social media ban consultation comes to close
CIOB urges UK Government to consider social media’s role in careers guidance in ban debate.
The latest of eight Skills England apprenticeship units
The addition of battery manufacturing welcomed by ECA with a warning about the risks of fast-tracked apprenticeship units.
Building Control Independent Panel final report
A precis of a key report led by Dame Hackitt with full recommendations and link to the government response.
Building Safety recap April, 2026
A short and longer run-through of the month, with links to further information and sources.
CIAT May 2026 briefing.
From medieval scribes to modern word art.
ECA welcomes crackdown on late payment and push for clean energy, whilst CIOB seek fixed cladding removal timeframes.
Cyber Security in the Built Environment
Protecting projects, data, and digital assets: A CIOB Academy TIS.
Managing competence in the built environment
ITFG publishes new industry guide on how to meet the ICC principles.
The UK's campaign to reduce noise pollution: Mythbusting, articles and topic guides.