Human-centric lighting: what buildings get wrong

The phrase human-centric lighting now appears in a great many commercial specifications. Architects know it, lighting designers use it and facilities teams have heard it. Yet a lot of what is installed under that name is still designed in the traditional way: for visual comfort and for light on the desk.

That is not a criticism of the people doing the work. The research has moved quickly, and standards and products are still catching up.

What human-centric lighting actually means

The term is used loosely. Sometimes it means little more than dimming with daylight sensors, or fittings that shift between warm and cool white. Those features can be useful, but they are not the point.

Human-centric lighting starts from the people in the building. It considers visual comfort, but also the non-visual effects of light, above all its role as the main timing signal for the body clock. That signal comes from specialised light-sensitive cells in the eye that are separate from the ones we use to see. Design for them, as well as for vision, and you are doing human-centric lighting. Design only for vision, and you are not, whatever the label says.

For the basics of how light sets the body clock, see our guide Circadian lighting explained.

Where specifications fall short

1. Measuring at the desk, not at the eye

Most lighting calculations focus on horizontal illuminance on the working plane. The body clock responds to light entering the eye, which depends on vertical light, room surfaces and where people look. A room can meet its desk targets comfortably and still deliver very little of the signal that matters for the body clock.

2. Treating colour temperature as a biological measure

Correlated colour temperature, or CCT, describes how warm or cool white light looks. It is a visual measure. Two sources with the same CCT can differ noticeably in how strongly they act on the body clock, because what matters is the make-up of the light, not its apparent colour. Programming a schedule of colour temperatures across the day is a reasonable start, but on its own it does not tell you what the occupants receive.

3. Static schemes in dynamic buildings

People need different light at different times of day, and different people need different things. Daylight changes by the hour and by the season. A fixed installation, however carefully specified, cannot respond to any of that.

4. Forgetting the evening

Good human-centric design considers when to reduce stimulating light, not only when to add it. This matters most in places people use late in the day or overnight, such as hospitals, care settings and hotels.

Tunable white is a tool, not a solution

Tunable white fittings shift between warmer and cooler white. They can be part of a good human-centric scheme. But a fitting that changes colour temperature on a timer is not, by itself, circadian lighting. Before treating a product as a circadian solution, ask the manufacturer for its melanopic data across its settings. If they cannot provide it, the product was designed for appearance, and the circadian claim came later.

The measures that matter

In 2018 the International Commission on Illumination published CIE S 026, which defines how to measure the non-visual effects of light. Its melanopic equivalent daylight illuminance, often shortened to melanopic EDI, is now the reference measure for how strongly light acts on the body clock. The WELL Building Standard includes a circadian lighting feature based on melanopic light at the eye, and other frameworks are moving the same way.

For specifiers, the practical change is simple to state: design to melanopic targets at eye level, not only to lux on the desk.

What good specification looks like

• Start with the people and the hours they keep, not the fitting schedule.
• Model and measure light at the eye, using melanopic measures alongside photopic ones.
• Plan how light should change across the day and into the evening.
• Integrate daylight, and let artificial light adapt to it.
• Ask suppliers for melanopic performance data, and test claims against it.

The opportunity

Healthier buildings are becoming an expectation for occupiers, investors and certification schemes. Specifiers who understand the science now will be better placed as requirements tighten, and better able to tell genuine human-centric lighting from a label.

At Sensio BioLabs we study the light people actually receive, at the eye and through the day. If you work in lighting, building design or research and would like to compare notes, get in touch.