LED lighting and your commercial EPC rating
Updated 19 October 2026 · SEO Dons Editorial
Lighting can carry a lot of weight in a commercial EPC because the calculation models the lighting in every zone, and in some non-domestic buildings lighting accounts for more of the modelled carbon emissions than heating. An LED upgrade improves the rating only as far as the assessor can record it, and that depends on evidence: the efficacy of the fittings in lumens per circuit-watt, and the controls that switch or dim them. Without that evidence the assessor has to fall back on a generic lamp type.
Why does lighting carry so much weight in a commercial EPC?
Lighting is one of the core inputs. The government guide to EPCs for non-dwellings lists it among the key factors in the rating, alongside the construction, the zones and their occupancy, and the heating, cooling, ventilation and hot water systems. The carbon-based rating a building receives depends on the energy used for space heating, water heating, ventilation and lighting.
The official National Calculation Methodology (NCM) website, which hosts the SBEM calculation tool, makes the point directly: in some non-domestic buildings, heating is responsible for only a small proportion of total carbon dioxide emissions compared with lighting, so further insulation can have a limited effect on the result. How much lighting matters in your building depends on the activities in it, because the guide notes that different activities carry different requirements for lighting as well as for heating and hot water.
Two quirks are worth knowing. First, lighting does not decide whether a building needs an EPC: the trigger is fixed heating, mechanical ventilation or air conditioning, and the guide says the same argument that rules out hot water applies to electric lighting. Once an EPC is needed, though, the lighting counts in full. Second, the rating assumes standardised use, so lighting hours come from the activity assigned to each zone, not from your switching habits. A switch-off campaign saves money but does not change the score. Automatic controls that the assessor can record are a different matter.
What is lighting efficacy, and how does the assessor enter it?
Efficacy is the light delivered for the electricity used, expressed in lumens per circuit-watt (lm/cW). Approved Document L defines circuit-watts as the power consumed in lighting circuits by the lamps and, where applicable, their control gear, including transformers and drivers. That is why a figure for the complete fitting tells the model more than a lamp wattage on its own.
The Non Domestic EPC Conventions for England and Wales, which accreditation schemes issue to non-domestic energy assessors, set out three ways to enter lighting in SBEM:
| Route | What the assessor needs | What the model uses |
|---|---|---|
| Full lighting design | The building's original lighting design, with wattage and lux values that match the lighting seen on site, or wattage and lux recorded accurately by the assessor | The installation's own design values |
| Efficacy and light output ratio | Both the lumens per circuit-watt and the light output ratio (LOR) of the fittings, with the source of the figures recorded in the site notes | The products' stated performance |
| Lighting parameters not available | Only the lamp type in each zone | A standard lamp type rather than your products' data |
The conventions rule out shortcuts. Wattage and lux values cannot be entered separately, and assessors may not use assumed values from reference publications or accept software-suggested defaults. Lux readings taken by an assessor only count if they were recorded in line with the Society of Light and Lighting's Code for Lighting 2009, with evidence of a complete blackout of windows.
For LED fittings, the light output ratio matters. If the lumens per circuit-watt figure is known for the entire fitting, including integral LED chips, the LOR is taken as 1. If the figure is only known for the lamp, the luminaire's LOR must also be obtained, unless it is a directional downlight-type lamp not shielded by the luminaire or a diffuser. A non-directional bulb-type lamp cannot be assumed to have an LOR of 1, even without a shade.
How do lighting controls affect the rating?
The assessor records the lighting and its controls zone by zone, so controls are part of what the model credits. Daylight is handled through zoning: the NCM website confirms that dividing zones according to daylight is part of the NCM zoning rules, and that the assessor can enter the percentage of each zone where lighting responds to daylight. Entering 100% means the whole zone has daylight-responsive lighting controls.
Display lighting is treated separately from general lighting, which matters for shops and showrooms. Where a zone's activity assumes display lighting but none is fitted, its efficiency is entered to match the general lighting in that zone. Where display lighting is present, the conventions accept that calculating its efficiency is not usually practical in existing buildings and set a default: for lamp types other than tungsten or tungsten halogen, the assessor enters 50 lm/cW unless a lighting design gives a specific figure. An efficient LED display scheme is therefore modelled at that default unless a lighting design supplies its actual efficacy.
What evidence does the assessor need to see?
Information has to be checked on site. The government guide says that, even where detailed plans exist for an existing building, the assessor must validate them through a site inspection. Documents can fill gaps, but only if they can be tied to what is there: the conventions' general rule is that there must be a demonstrable link between visual observations on site and the documentary evidence used, such as a model number on a fitting that matches a manufacturer's data sheet.
Evidence the conventions list as acceptable includes:
- manufacturer's technical data sheets
- technical design information, including the lighting design
- purchase orders and delivery notes
- installation, service and maintenance records
- operation and maintenance manuals or user guides
- letters or emails from the architect, engineer or manufacturer's technical support
- building control sign-off sheets
Where the assessor relies on the design team's documents, they must be as-built: the conventions say design documentation alone is not acceptable. Two further conventions show how gaps are filled when evidence is missing:
- Older fluorescent tubes: T8 lamps are only entered as high-frequency if images or documents support it; otherwise the worst case, low-frequency operation, is assumed.
- Empty fittings: where no lamp is fitted, the assessor selects CFL for fittings that will take one, or the least efficient lamp type the fitting can house. If no fittings are present, or the lamp type cannot be established, CFL is the default.
In practice, before the survey: make sure every area is lit and accessible, keep a schedule of fitting types by area with model numbers, gather the data sheets and any lighting design, and have commissioning records for presence and daylight sensors to hand. The guide to heating and cooling controls applies the same evidence principle to plant.
Does Part L set its own standard for new lighting?
Yes, and it is a separate test from the EPC. In England, Approved Document L, Volume 2 (2021 edition incorporating 2023 amendments) covers fixed building services installed in existing buildings as well as new ones. For general lighting it expects an average luminaire efficacy of 95 luminaire lumens per circuit-watt, or use of the Lighting Energy Numeric Indicator (LENI) method, and for display lighting an average light source efficacy of 80 light source lumens per circuit-watt or one of the alternatives. It also expects automatic controls such as presence detection to switch general lighting off in unoccupied spaces, daylight controls such as photo-switching and dimming where occupied spaces get high levels of natural light, and metering of general and display lighting.
A 2026 edition has been published and takes effect on 24 March 2027 for building work in England that is not connected with higher-risk building work. It raises the general lighting figure to greater than 105 luminaire lumens per circuit-watt. Earlier editions continue to apply to buildings subject to previous standards, so confirm which edition applies with the installer or building control body. Meeting Part L does not change the EPC by itself; the rating only moves when a new EPC records the new installation.
Will an LED upgrade be enough to change the band?
It depends on the building, which is why the recommendation report is the place to start. If it lists lighting measures, it shows which payback group each falls in and its potential impact on carbon emissions. For buildings rated F or G, the usual order of improvements is covered in Rated F or G? What it means and how to fix it, and possible funding routes for the works are on the grants and funding page.
Whatever the works, the published rating only changes once a new EPC is lodged, because until then the existing certificate stays the valid one. When the upgrade is finished and the evidence is gathered, you can ask for quotes for a reassessment through this site's form, and the enquiry is passed to companies that carry out commercial EPCs.
Sources
- A guide to Energy Performance Certificates for the construction, sale and let of non-dwellings, Ministry of Housing, Communities and Local Government (GOV.UK), checked 19 October 2026.
- NCM and SBEM frequently asked questions, uk-ncm.org.uk (BRE, official NCM and SBEM website), checked 19 October 2026.
- Non Domestic EPC Conventions for England and Wales, Issue 9, NDEPC Conventions Group, published on uk-ncm.org.uk, checked 19 October 2026.
- Approved Document L, Volume 2: Buildings other than dwellings, 2021 edition incorporating 2023 amendments, Department for Levelling Up, Housing and Communities (GOV.UK), checked 19 October 2026.
- Approved Document L, Volume 2: Buildings other than dwellings, 2026 edition, Ministry of Housing, Communities and Local Government (GOV.UK), checked 19 October 2026.
- Approved Document L: Energy and greenhouse gas emissions (2026), Ministry of Housing, Communities and Local Government (GOV.UK), checked 19 October 2026.
- The Energy Performance of Buildings (England and Wales) Regulations 2012, regulation 9, legislation.gov.uk, checked 19 October 2026.
Common questions
Do LED lamps in old fittings count the same as new LED luminaires?
Not necessarily. Under the EPC conventions, a lumens per circuit-watt figure for the whole fitting, including integral LED chips, is used with a light output ratio of 1, but a figure for the lamp alone also needs the luminaire's light output ratio, unless it is an unshielded directional downlight. Without either, the assessor enters a generic lamp type.
Will switching lights off more often improve the EPC?
No. The model uses standard hours for each zone's activity, so behaviour is not an input. Automatic controls such as presence detection or daylight dimming are different, because the assessor records the controls fitted in each zone.
Can the assessor take light readings instead of using data sheets?
Only under strict conditions. The conventions allow lux readings taken by the assessor only if they were recorded in line with the Society of Light and Lighting's Code for Lighting 2009, with evidence of a complete blackout of windows and the grid calculations used.
If the lighting is upgraded after the EPC, does the certificate update itself?
No. Once an EPC is registered it cannot be altered, and it stays the valid certificate until it is 10 years old or a newer EPC is lodged. A new assessment is needed for the upgrade to show.