part l lighting regulations

Part L for Lighting

In this post the lighting design studio offer an explanation of Part L lighting, and sets out the requirements your lighting needs to meet.

So what is Part L for Lighting?

It’s a UK building regulation issued by the Secretary of State which lays down specific measures for the conservation of fuel and power. It is now a general aim to make our buildings as energy efficient as possible and therefore efficient electric lighting is required in most buildings. You will have to comply with this regulation when your building has been extended or when your existing lighting system is being replaced as part of re-wiring works.

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The latest edition came into effect on 6th April 2014 and is split into four categories:

Part L Lighting
Part L Lighting

L1A New dwellings.

L1B Existing dwellings.

L2A New buildings other than dwellings.

L2B Existing buildings other than dwellings.


Both L1A and L1B documents refer to the Domestic building compliance guide which can be downloaded from the governments planning portal:


Documents L2A and L2B refer to the Non-domestic building compliance guide, again available on the governments planning portal:


Why is it important?

Building regulations are legal requirements. You have a responsibility for ensuring compliance with building regulations and could be served with an enforcement notice, prosecuted and fined in cases of non-compliance.


What are the key points & how do you comply?


In the Domestic building compliance guide, for the lighting part you can skip direct to Section 12 (page 81). To comply, in new dwellings (L1A) 75%, so 3 in every 4 of the fixed internal light fittings need to have a minimum of 45 lamp lumens per watt. They also need to an output greater than 400 lamp lumens to count.

Products that are not fixed like table and bedside lamps, light fittings under 5 watts or products located in spaces that are not used often, like store cupboards and wardrobes can be excluded.

With fixed external lighting, in new dwellings, products need to either be under 100 watts and automatically controlled with a light sensor to switch them off when daylight is sufficient. Or have a lamp efficacy greater than 45 lumens per Watt and again controlled with a light sensor, although you can also have these manually controlled if required.

Existing dwellings – (L1B) generally refers to new extensions, loft conversions and renovations. Typically the above criteria applies to the newly built or renovated area and the rest of your house would be exempt. However, this is not always the case and if you have any doubts we would advise you to check at the design stage with the lighting design studio or consult your local building controls officer.


Buildings other than dwellings

In the non-domestic building compliance guide again you can skip to Section 12 (page 65) for the lighting part. Importantly, for this section the regulation makes a clear definition between luminaire lumens and lamp lumens. Light fittings, often referred to as Luminaires, are not 100% efficient and a proportion of light is absorbed or blocked by the reflector, diffuser, or lamp shade. Luminaire lumens is the amount of light (lumens) produced by a product after you take into account these losses (us lighting designers also call this the light output ratio or LOR). This is crucial because even light fittings that use very efficient lamps (light bulbs) or LEDS can still be inefficient, particularly those with thick diffusers.

In non domestic situations (new buildings other than dwellings L2A), for lighting to comply with Part L, the sum of all general light fittings in office, industrial and storage areas need to average 60 luminaire lumens per circuit watt.

For general lighting in ‘other’ types of space, the sum of all fittings should have an average efficacy of 60 lamp lumens per watt. And 22 lamp lumens per watt for display lighting.

Lighting controls are also taken in to account and if a control system is used, the lighting can achieve a slightly lower figure depending on method of control.

Existing buildings other than dwellings (L2B) again typically applies to new extensions, renovations and change of use. As before, generally the above criteria is only applicable to the newly built or refurbished part of the building. Although this is not always the case.

There are certain buildings that have an exemption from compliance, listed buildings, monuments, places of worship, and temporary buildings for example. If you are not sure if your building needs to comply please contact the lighting design studio for guidance.



LENI (Lighting Energy Numeric Indicator) has also been included as an alternative to minimum luminaire lumens per circuit watt. So there are now two options to calculate energy use and show compliance.

LENI is a change of philosophy, looking at energy use rather than installed load. It measures predicted energy used by a lighting system over the length of a year (measured in kilowatt hours, per square metre, per year) so it looks at the complete system, rather than individual luminaires. At the lighting design studio generally we think this amendment is brilliant news. In the conventional method of calculation compliance, non domestic buildings areas that are not classed as office industrial or storage, use lamp lumen ef­ficacy as the metric.  So providing a product uses an efficient lamp, the light fitting would comply. With LENI manufacturers are being pushed to deliver more ef­ficient luminaires – which is great. Also in the amendments occupancy and daylight controls are no longer the only deliverable and measured controls, which is good because in a space with plenty of sunlight, electric light is not needed for most of the year, but the control factor of 0.9 used in the conventional method doesn’t reflect this. LENI a control system can deliver up to 30 per cent reduction on the original luminaire ef­ficacy (a control factor of 0.7) which is very important. It means we are no longer forced to use inappropriate light fittings because of their ef­ficacy. We can look at using more appropriate but less efficient products in our designs, providing we control them properly. Calculating LENI is more complex as we need to know the total installed power, the area being lit and the number of hours that electric light is required during the year. Part L uses a shorter simplified version of LENI which unfortunately doesn’t make allowance for daylight as a principal light source. Perhaps the next iteration of Part L will make this next step.


So who enforces this?

The role of checking that building regulations are being complied with falls to Building Control Bodies (BCBs). There are two types – the Local Authority Building Control (LABC) or a private sector Approved Inspector Building Control (AIBC). Customers are free to choose which type of Building Control Body they use on a project. In addition a competent person scheme has been introduced by the Government to allow individuals and enterprises to self-certify that their work complies with the Building Regulations as an alternative to submitting a building notice or using an approved inspector.

For dwellings (parts L1A & L1B) if you are carrying out any electrical work and / or adding fixed lighting to the outside of your house, in England and Wales you have to follow building regulations including Part L. You should either use an installer who is registered with the competent person scheme. Who should make sure your lighting complies with Part L and submit a SAP (Standard Assessment Procedure) or make an application to your local authority’s building control department or approved inspectors.

For Non dwellings (parts L2A & L2B) the methodology for proving compliance is the SBEM (Simplified Building Energy Model) and you will need to ensure that a Buildings Emission Rate for carbon dioxide (BER) is better than the Target Emission Rate (TER). If it fails there may be additional remedial work to ensure that the whole building complies.


As you can see from this post, Part L is complex and it can be quite hard to make sure a lighting scheme complies. At the lighting design studio we feel it’s understandable that regulations are getting tougher. We live in times where the impact of global warming and rising electricity costs is a real issue. If government regulation helps push people into using existing much more efficient technology it’s a good thing, as with most new technologies, people can be slow to adapt, most people don’t like change. If you have any questions or need help ensuring your project complies with Part L, then please do get in touch.