What counts as a failed lux survey?
A lux survey does not have a single pass mark. Each measured area is compared against the benchmark that applies to the task carried out there, usually the maintained illuminance, uniformity and glare values in BS EN 12464-1:2021, with HSE guidance HSG38 Lighting at work as the minimum floor and the legal duty in regulation 8 of the Workplace (Health, Safety and Welfare) Regulations 1992 that lighting must be “suitable and sufficient”. An area “fails” when one or more of those values is not met under normal operating conditions.
In practice a report rarely says “the building fails”. It flags specific rooms, zones or workstations, explains which parameter fell short and by how much, and prioritises what to fix. If you want a primer on how readings are taken first, see how lux is measured.
The seven failures we see most often
1. Average illuminance below the recommended level
The most obvious failure. A general office should achieve a maintained average of 500 lx on the task area; a corridor 100 lx; a manned warehouse rack gangway 150 lx. Common causes are failed lamps or drivers, luminaires spaced for a previous layout, ceiling heights raised in a refit, or simply a design that never achieved the target. A shortfall of 10–15% is often recoverable by cleaning and replacing failed units; a shortfall of 40% or more usually means the installation itself is under-specified.
2. Poor uniformity
Uniformity (Uo) is the ratio of the minimum reading to the average. BS EN 12464-1:2021 asks for 0.60 on most office task areas and 0.40 in circulation spaces. A room can have a healthy average and still fail because desks between luminaires sit in dark bands, or because one row of fittings is out. Uniformity failures are especially common after partitions or tall storage are added without moving the lighting.
3. Glare (UGR too high)
The Unified Glare Rating limit for offices is 19; industrial and circulation spaces allow higher values. Bare LED battens, high-output panels without suitable diffusers and fittings moved to awkward positions are the usual culprits. Glare is assessed from the luminaire data and room geometry rather than a single meter reading, which is why a good survey records fitting types and photometry, not just lux. We cover this in detail in can an LED upgrade reduce compliance?
4. Dark walls and ceilings
The 2021 edition of BS EN 12464-1:2021 places more emphasis on illuminance reaching walls and ceilings, because a room lit only at desk height feels gloomy even when the task numbers pass. Narrow-beam downlights and high-output panels pointed straight down are the typical cause.
5. Emergency escape lighting below BS EN 1838:2024
Escape routes up to 2 m wide need at least 1 lx along the centre line, and open (anti-panic) areas at least 0.5 lx, measured with normal lighting off. We regularly find fittings that pass the monthly flick test but whose batteries no longer last the rated duration, or new partitions that leave a corridor end unlit. Testing regimes are set out in BS 5266-1:2025 and the duty sits under the Regulatory Reform (Fire Safety) Order 2005. See our emergency lighting lux survey service.
6. Flicker and poor colour rendering
Cheap LED drivers can produce visible flicker or stroboscopic effects near rotating machinery, a genuine safety issue in workshops. Colour rendering below Ra 80 in offices, or below the higher values needed for inspection and colour-matching tasks, is another frequent finding after budget retrofits.
7. Lighting that no longer matches the use
A storeroom becomes a packing bench; a meeting room becomes a drawing office. The lighting was right for the original purpose and is now wrong. Change-of-use is behind a large share of the failures we report.
Typical failure causes and fixes
| Finding | Usual cause | Typical fix |
|---|---|---|
| Average 10–20% low | Dirt, failed lamps/drivers, ageing output | Clean, replace failed units, re-survey |
| Average 30%+ low | Under-designed or re-planned space | Add or re-space luminaires, redesign |
| Uo below 0.60 (office) | Fitting spacing, partitions, outages | Re-position fittings, add infill lighting |
| UGR above 19 (office) | Unshielded or high-luminance fittings | Low-glare optics, diffusers, re-orientation |
| Escape route below 1 lx | Battery failure, layout changes | Replace batteries/fittings, add points |
| Visible flicker | Low-quality LED drivers | Replace drivers or luminaires |
Sector-specific patterns
Offices
Uniformity and glare are the usual problems rather than raw lux. Hot-desking layouts that ignore the lighting grid leave some desks well under 500 lx. See office lighting standards.
Warehouses and industrial units
Racking that has grown taller or been re-aligned blocks light from high-bay fittings, so the aisles fail even when the open floor passes. Loading bays and yard areas are often forgotten entirely. Our warehouse lux survey covers rack faces, gangways and external areas.
Schools, care homes and healthcare
Here failures tend to be about suitability rather than quantity: glare at whiteboards, night lighting that is too bright or too dim, and examination areas that lack the higher illuminance and colour rendering they need.
Why it matters
A documented shortfall is not automatically a breach of the law, but once you know about it you are expected to act. Insurers, landlords and HSE inspectors look for evidence that lighting has been assessed and that failures have been dealt with. A short remedial plan, followed by a re-check of the affected areas, is usually enough to close the issue.
Book a survey to find your failures first
It is far cheaper to find a lighting failure yourself than to have it raised after an accident, an inspection or a tenant complaint. Polarity Lux carries out lux surveys across London and the South East, including Hertfordshire, Essex, Kent and Surrey. A spot check starts from £90 and a full single-floor office or retail survey from £175. Book your lux survey and we will tell you exactly which areas fall short and what to do about it.
Frequently asked questions
What is the most common reason a lux survey fails?
Poor uniformity and low average illuminance are the most common, usually caused by failed fittings, dirt, or luminaire layouts that no longer match the room layout.
Is a failed lux survey a breach of the law?
Not automatically. The legal duty is for suitable and sufficient lighting under regulation 8 of the Workplace Regulations 1992, but once a shortfall is identified you are expected to assess the risk and put it right.
Can cleaning luminaires fix a failed survey?
Sometimes. Where the shortfall is modest and caused by dirt or failed lamps, cleaning and replacing units can bring readings back within range, but a re-check should confirm it.
Do you re-test after remedial work?
Yes. We can re-survey only the areas that failed, so you have documented evidence that the issue has been resolved.