Lighting by building type: what changes, and what does not

The physics does not change between building types. What changes is which constraint governs — and that single question reorders every decision after it.

In an office the governing constraint is a standard. In retail it is a contrast ratio. In a museum it is conservation. Get that right and the scheme almost designs itself; get it wrong and you can meet every number in the code and still produce a room nobody wants to be in.

Office

Governed by: EN 12464-1 and the energy code, simultaneously.

The numbers. 500 lx maintained on the task area, UGR ≤ 19, Uo ≥ 0.60, Ra ≥ 80. The 2021 edition also asks for cylindrical illuminance ≥ 150 lx and walls ≥ 75 lx, ceiling ≥ 50 lx — requirements a downlight-only scheme quietly fails.

The mistake. Treating it as a lux problem. A room at 500 lx with dark walls and a dark ceiling reads as oppressive, scores badly on UGR because the background luminance is low, and fails the new vertical requirements. Lighting the walls fixes all three at once, and usually costs less than adding more downlights.

The thing everyone forgets. Video calls. Faces are lit from above by a downlight-only scheme, which produces eye sockets in shadow and a shadow under the chin. Vertical light from in front — a wall wash on the wall people face — is the cheapest fix there is.

Retail

Governed by: contrast ratio, not illuminance.

The numbers. EN gives 300 lx for the sales area as a floor, but nobody designs to it. The working figures are ratios: feature to ambient between 3:1 and 10:1, with 15:1 reserved for genuine drama. Ra ≥ 90 and R9 ≥ 50 as a minimum, higher for food and cosmetics.

The mistake. Raising the ambient. Every increase in the general level flattens the contrast that makes merchandise read, so the room gets brighter and less effective at the same time. If a display is not standing out, lower the surroundings before raising the accent.

Fitting rooms deserve their own paragraph. High Ra with strong R9, soft, vertical and from the front, at around 500 lx. A downlight over a mirror gives every customer eye bags and a double chin, and clothes go back on the rail.

Hospitality

Governed by: atmosphere, which is not a metric — so the constraint is the control system.

The numbers. Deliberately sparse. EN 12464-1 does not regulate restaurant dining because there is no visual task. Reception is 300 lx, kitchens 500 lx. Everything else is judgement.

What actually decides it. Scenes. A lobby needs at least four states — morning, day, evening, night — and a restaurant the same. Write the scene schedule in detailed design: room, name, groups, levels, CCT, fade time, trigger. Without it, commissioning becomes improvisation and the space ends up permanently at one setting.

The mistake. Specifying tunable white without deciding who changes it. An unmanaged tunable installation is a fixed installation at whatever CCT it was left on, at a substantial premium.

And the detail that carries the whole room: 2700 K, Ra ≥ 90 with real R9, dimmed low, with the sources hidden. Warm, high-quality, low-level light on faces is what people remember as “nice lighting” without ever being able to say why.

Museum and gallery

Governed by: conservation. This is the one typology where the limit is the artefact, not the viewer.

The numbers. Exposure is what damages, and exposure is lux × hours:

Material	Limit
Textiles, works on paper, dyed leather	50 lx, ≤ 15,000 lx·h/year
Oil and tempera, undyed leather, bone	150–200 lx, ≤ 600,000 lx·h/year
Metal, stone, glass, ceramic	No limit

Ra ≥ 90 throughout, and UV must be excluded entirely.

Why the annual figure matters more than the instantaneous one. 50 lx for eight hours a day, 300 days a year is 120,000 lx·h — eight times over budget for a textile. Either the object is rotated out of display, or the lighting is on occupancy control, or both. That is a curatorial conversation, and it belongs at concept stage.

The mistake. Ignoring adaptation. A 50 lx gallery entered directly from a daylit lobby reads as pitch black, and visitors will report that they “cannot see the objects” even though the level is correct. Design the transition — 300 lx, then 100 lx, then 50 lx — and the same gallery reads as intimate.

Healthcare

Governed by: multiple conflicting requirements in the same room, which is what makes it hard.

The numbers. A single ward bed needs at least four states: general 100 lx, reading 300 lx, examination 1000 lx at Ra ≥ 90, and night-watch ≤ 5 lx. Each needs separate control, and the examination scene needs genuinely good colour because tissue colour is diagnostic.

The mistake. Treating the night scene as a dimmed day scene. A 4000 K source dimmed to 5% still has high melanopic content per lux and keeps both patients and staff alert. The night state should be warm — 2200–2700 K — and mounted low, so it lights the floor rather than the patient’s eyes.

Staff matter as much as patients. Night-shift workers are the population most affected by circadian disruption in the whole building, and staff bases are where a considered scheme does the most good.

Residential and high-end apartments

Governed by: the fact that nobody is being paid to operate it.

The numbers. Almost none apply. This is a typology of judgement.

What decides it. Layers on separate circuits, and controls simple enough that a guest can use them. Four keypad buttons labelled in plain language beat forty addressable groups nobody understands.

The mistake. Over-specifying control. A system that needs an app, a login and a firmware update will be bypassed within a year, and the client will leave every light on one circuit at 100%.

In Vietnam specifically: balconies, light wells and semi-outdoor spaces blur the line between interior and exterior. Fittings in those positions are exterior fittings — IP rating, corrosion resistance and surge protection all apply, even though the space reads as indoors.

What stays the same everywhere

Four things do not change with typology, and they are worth holding onto when a project’s specific demands start crowding everything else out.

Light the vertical surfaces. Walls, not floors, are what people see. This is true in every building type without exception.

Hide the source. Glare is the failure people actually complain about, and cut-off is the most reliable tool against it.

Layer, and put the layers on separate control. Any room worth lighting needs at least two independently controlled layers.

Mock up anything where a material is doing the work. No calculation predicts how a specific stone reads under a specific grazing angle, in any typology.