A Wake-Up Call: We Are Designing Light Against Human Biology

Last week, Jan Denneman had the opportunity to speak at Light + Building in Frankfurt as Chair of the Good Light Group.

What continues to strike him is this: we spend around 90% of our time indoors, yet the light around us is fundamentally misaligned with our biology. The impact is not subtle. It shows up in poor sleep, low energy, reduced wellbeing, and long-term health risks.

And still, we treat this as normal.

The reality is simple. During the day, most indoor environments are far too dim to properly stimulate our circadian system. In the evening, they are often too bright, sending the wrong signals to our body when it should be preparing for rest. On top of that, artificial light differs significantly from natural daylight in its spectral composition. We are, quite literally, designing light against human biology.

Science has already given us clear guidance. During the day, we need around 500 to 1,000 lux at eye level to properly stimulate our circadian system. In the evening, light levels should drop below 20 lux, and at night to almost complete darkness. Yet in practice, most people receive only a fraction of the light they need during the day, unless they are sitting right next to a window. The result is a continuous disruption of our internal clock.

The consequences are significant and well documented. Light affects how we sleep, how we feel, how we perform, and how healthy we are over time. If we improved sleep alone through better lighting, the economic value would be enormous.

So why is this not happening at scale?

Because we are still optimising for the wrong thing.

The 3–30–300 rule makes this painfully clear. For every €3 spent on energy and €30 on the building, organisations spend around €300 on the people inside (per 0.1m² per year). Yet lighting decisions are still largely driven by saving a fraction of the €3, while ignoring the much larger impact on the €300.

This is where the real opportunity lies. Not in squeezing out another percentage of energy savings, but in improving human health, wellbeing, and performance through better light.

Indoor lighting should not be treated as a purely technical or efficiency-driven system. It is a health intervention hiding in plain sight.

That means this is not just a topic for the lighting industry. It is a responsibility across the entire ecosystem shaping our indoor environments, from designers and architects to installers, building owners and investors, and not least employers who care about the wellbeing of their people.

In this short clip, Jan explains why it is time to rethink how we design light indoors, and why the cost of inaction is far greater than we tend to assume.

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