Why the average lux level is only part of the picture
When people ask “how many lux does my office need?” they usually mean the average. BS EN 12464-1:2021 does specify an average – the maintained average illuminance – but it pairs every value with a uniformity requirement. A space can hit its average comfortably and still fail because light is unevenly spread. To judge lighting properly you need three numbers: the average, the minimum and the uniformity.
Average, minimum and uniformity explained
Average illuminance (Ē)
The mean of all readings taken across the measurement grid for an area. It describes the overall quantity of light. In BS EN 12464-1:2021 the target is a maintained value, meaning the average must not fall below it at any point before scheduled maintenance. For how the grid is set out, see how is lux measured?
Minimum illuminance (Emin)
The lowest single reading on the grid. It identifies the darkest spot in the working area, often between luminaires, behind racking or beside a failed fitting.
Uniformity (Uo)
Uniformity is the minimum divided by the average: Uo = Emin ÷ Ē. A value of 1.0 would mean perfectly even light. BS EN 12464-1:2021 sets minimum uniformities, typically 0.40 for circulation and storage areas and 0.60 or higher for tasks requiring sustained concentration. Poor uniformity forces the eye to keep adapting between bright and dark patches, which causes fatigue and makes hazards harder to spot.
A worked example
Consider an open-plan office measured on a grid of 40 points. The readings give an average of 520 lux and a minimum of 260 lux.
- Average: 520 lux against a target of 500 lux – pass.
- Uniformity: 260 ÷ 520 = 0.50 against a target of 0.60 – fail.
Overall, the area does not comply, even though the headline average looks fine. This pattern is very common after an LED upgrade where new fittings have a narrower beam than the originals, or where luminaires have been spaced too far apart. Raising the average by adding light everywhere would not fix it; repositioning or changing the optics would.
Average lux levels by industry
The figures below are selected maintained illuminance and uniformity values from BS EN 12464-1:2021. Each task has its own table entry, so always check the specific activity rather than relying on a building type.
| Sector | Area or task | Average (lx) | Uo |
|---|---|---|---|
| All buildings | Corridors and circulation areas | 100 | 0.40 |
| Offices | Writing, typing, reading, data processing | 500 | 0.60 |
| Warehousing | Storage areas | 100 | 0.40 |
| Warehousing | Packing and dispatch | 300 | 0.60 |
| Retail | Sales areas | 300 | 0.40 |
| Education | Classrooms (general) | 300 | 0.60 |
| Hospitality | Commercial kitchens | 500 | 0.60 |
| Healthcare | Examination and treatment | 1000 | 0.70 |
For a fuller list by sector, use our recommended lux levels chart.
Offices
500 lux on the task area with Uo 0.60 is the standard benchmark for desk work. The immediate surrounding area can be one step lower. CIBSE LG7 adds guidance on wall and ceiling brightness, which strongly affects how bright an office feels. See office lighting standards.
Warehouses and logistics
Storage aisles may only need 100 lux, but picking from labels, packing and dispatch need 300 lux. Vertical illuminance on racking faces matters as much as the floor, because that is where labels are read. High-bay fittings spaced for an empty shell often fail once racking is installed.
Schools
Classrooms generally need 300 lux with Uo 0.60, rising to 500 lux for evening classes and adult education. DfE BB90 adds guidance on daylight and lighting design for schools.
Healthcare
General areas in surgeries and clinics are lower, but examination and treatment tasks need 1000 lux with higher uniformity. Healthcare lighting is also guided by HTM/HBN and SLL LG2.
HSE minimum lux levels
HSE guidance HSG38 Lighting at work gives a separate, lower set of figures. These are minimums intended to protect health and safety, not recommended design levels. Each has an average and a minimum measured value.
| Activity (HSG38) | Average (lx) | Minimum measured (lx) |
|---|---|---|
| Movement of people, machines and vehicles | 20 | 5 |
| Movement in hazardous areas; rough work | 50 | 20 |
| Work requiring limited perception of detail | 100 | 50 |
| Work requiring perception of detail | 200 | 100 |
| Work requiring perception of fine detail | 500 | 200 |
Meeting HSG38 shows the absolute floor has been cleared. Meeting BS EN 12464-1:2021 shows the lighting is suitable for the task, which is the stronger position if lighting is ever questioned. See HSE lighting requirements.
Common reasons averages mislead
- Too few readings: a handful of points under luminaires overstates the average and misses dark spots.
- Daylight included: a sunny afternoon can flatter results that fail after dark.
- Wrong height: floor readings in an office understate desk illuminance; desk readings in a corridor are irrelevant.
- Whole-room averaging: averaging a bright desk zone with a dim storage corner hides failures in both.
Find out your real average lux levels
Polarity Lux measures average, minimum and uniformity for every area against the correct BS EN 12464-1:2021 entry, for premises across London and the South East. Book a lux survey with a fixed price confirmed in advance.
Frequently asked questions
What is a good average lux level for an office?
BS EN 12464-1:2021 recommends a maintained average of 500 lux on the task area for writing, typing, reading and data processing, with a uniformity of at least 0.60.
What is lighting uniformity (Uo)?
Uniformity is the minimum illuminance divided by the average illuminance across an area. A higher value means more even light; BS EN 12464-1:2021 typically requires 0.40 for circulation and storage and 0.60 for concentrated tasks.
Can a room pass on average lux but still fail?
Yes. If the darkest point is too low relative to the average, the uniformity requirement fails even when the average meets the target. This is common after LED retrofits with narrow-beam fittings.
What is the HSE minimum lux level?
HSE guidance HSG38 sets minimums by activity, for example an average of 200 lux and a minimum measured value of 100 lux for work requiring perception of detail. These are safety minimums rather than recommended design levels.