Everyone has read that lighting affects how people feel. Few things about our trade turn up in magazines. This one does. The useful question on a real project is narrower: which parts of it can you actually specify, and which parts are still a magazine sentence?

Here’s where we think the line sits. You can specify more of this than you might expect, and less than the magazines imply.

What the research supports, and how firmly

The clearest finding is about intensity. Research by Alison Jing Xu and Aparna Labroo, published in 2014 in the Journal of Consumer Psychology, found that more intense and bright the lighting the stronger the emotional response, in both directions. Bright light doesn’t make people happy. It makes them more of whatever they already were.

Colour temperature is the other half of the popular story, and it deserves more caution than it usually gets. Warmer light is associated with positive affect and cooler light with alertness, but the measured effects are modest and depend heavily on context: time of day, task, how long someone has been in the space. Real effect, weak lever. Copy that states it flatly is overselling it.

The workplace claim is worth restating properly too. Poor lighting does degrade how people work, but the mechanism is an ordinary one: glare, flicker, and too little light on the task cause visual fatigue and headaches. That’s a design failure with known causes and known fixes. Tell a client that, rather than a productivity percentage.

The part you can actually measure

Underneath the mood conversation is something harder-edged. The eye has a set of receptors that aren’t really for seeing. They respond most strongly to the blue end of light, and what they drive is the body clock rather than vision.

That matters for a practical reason. A light meter measures brightness the way your eye judges it, and those receptors don’t work the same way. Two fixtures can put the same amount of light on a desk and have a very different effect on how awake somebody feels. There’s a separate way of measuring the second thing, and it’s the one worth asking about if a project cares about this.

WELL puts real numbers on it

This is where it stops being a conversation and becomes something you can specify. The WELL Building Standard sets targets a design can be measured against, and the shape of them is more useful than the exact figures:

  • A high dose during the day, and the measurement is taken at eye level, facing the way people face — not on the desk.
  • A low dose in the evening, measured lower down, for spaces people occupy late.
  • Good colour rendering throughout — the same 80-and-up baseline that applies to everything else.

A lone worker seated at a desk in a large open-plan office lit only by computer screens, the rest of the room in darkness

Note what those measurements have in common. They are vertical, at eye height, facing the way the occupant faces. That isn’t how lighting is usually calculated, and it changes the answer.

Why the vertical plane changes the design

A ceiling grid can hit its horizontal target on the desk and still leave the eye in a dim room, because most of that light is travelling downward past the face. This is collected at the eye, not on the desk, so the design moves toward brighter walls, indirect light, and light arriving from where people are actually looking.

Which is a familiar conclusion arriving by an unfamiliar route: wash the vertical surfaces. Washing the walls is what makes a room feel bright, and it turns out to be what the body clock reads as well.

A woman smiling as she sits at a counter beside a large window in a daylit office entrance with a potted plant

Seasonal light, said carefully

Winter depression is the one place where light is used as a treatment rather than a design input, and the evidence there is genuinely strong. The Can-SAD randomized controlled trial, published in the American Journal of Psychiatry in 2006, compared bright light therapy against fluoxetine for winter seasonal affective disorder and found both effective, with no significant difference between them.

That is clinical light therapy: a prescribed device, a set duration, medical supervision. It isn’t a building lighting system, and nothing on this page is medical advice. We wouldn’t put a therapeutic claim on a luminaire, and neither should anybody else. What it does tell you is that the dose response is real enough to have survived a controlled trial, which is a reasonable argument for taking daylight access seriously in a floor plan.

A room at the Flux Lighting showroom in Ottawa taken down to a very low light level

What we would actually do

On a project where this matters, the work is sequencing rather than fixture selection. Tunable white gives you a colour temperature and an intensity that move through the day, and the value is entirely in the schedule behind it. A tunable system left at one setting is an expensive fixed system. That’s the failure mode we see most.

So: hold the brighter, cooler setting through the working morning, ease it back through the afternoon, and drop it hard in the evening for any space people occupy late. Then measure it on the vertical plane and see whether the room does what the drawing said. We run the calculation, and we’d rather run it before the ceiling is ordered.

Sources for the underlying research can be found here.

Common questions

Does lighting really change how people feel, or is that marketing?

Both, and the useful part is separating them. The eye carries a set of receptors that aren’t really for seeing, and what reaches them through the day genuinely affects alertness and sleep. That’s the substantiated half. Claims that a particular fixture will make a team happier or a room calmer are the marketing half, and they aren’t measurable.

What is human-centric lighting?

The name covers lighting designed around the daily rhythm rather than around a light level — brighter and cooler by day, dimmer and warmer in the evening. The idea has real evidence behind it. Plenty of product gets sold under the name that does nothing of the sort, so ask what specifically changes through the day, and when.

Is tunable white worth it?

Only if somebody is going to run it. Tunable white gives you a colour temperature and an intensity that move through the day, and the value is entirely in the schedule behind it. A tunable system left at one setting is an expensive fixed system.

Keep reading

  • Colour Temperature — Kelvin, colour rendering, and why one batch of fixtures can look different from the next.
  • Acoustic Lighting — what it fixes, and where it stops being the answer.

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