Beyond what we see – exploring the biological role of light

In conversations around wellbeing and the health of the human body, some researchers are beginning to ask whether light may influence the body in ways that extend beyond vision alone.

One of those researchers is neuroscientist Professor Glen Jeffery at UCL’s Institute of Ophthalmology, whose research explores the relationship between light, mitochondria, ageing and visual function, including the potential biological role of longer wavelengths beyond the visible spectrum.

This interview explores his research, insights, and the growing conversation about how modern indoor environments may be changing humanity’s relationship with light - not just visually, but biologically as well.

The Evolution of Humans Under Daylight

At the centre of Glen’s thinking is a relatively simple idea: the human body evolved under the full spectrum of sunlight over millions of years. “So many parts of your body and systems in your body were set over exposure to sunlight over millions of years,” he explains. “Your body has lost contact with your evolutionary history.”

He explains that this evolutionary perspective is central to understanding why light may matter biologically. Human physiology developed in outdoor environments where daylight exposure was continuous, dynamic and spectrally rich. Modern indoor life, by comparison, represents a dramatic environmental shift.

This does not mean modern lighting is inherently harmful, but rather society may only now be beginning to understand how profoundly modern environments have changed the way humans experience light.

Beyond the Visible Spectrum

When it comes to designing light, conversations often focus on what people can see: brightness, colour temperature, contrast, glare and visual comfort. Glen’s research, however, explores the possibility that wavelengths outside visible vision may also influence the body. “You only see a minute amount of the spectrum of sunlight, between roughly 400 nanometres (nm) to 700nm,” he explains.

Visible light occupies only a relatively narrow band within the wider electromagnetic spectrum. Beyond it sit ultraviolet wavelengths on one side and infrared wavelengths on the other - both largely invisible to the human eye.

Much of his recent work has focused on longer infrared wavelengths and their potential relationship with mitochondria - the structures within cells responsible for energy production.

He argues that much of the sunlight exists beyond the visible spectrum that humans experience with the naked eye. This is where the conversation begins to move beyond traditional lighting discussions and into broader biological territory.

Mitochondria, Energy and Ageing

A significant portion of his recent work has explored how longer wavelengths of light - particularly around 670nm and near-infrared ranges - may influence mitochondrial performance and age-related decline in both animals and humans.

A term many people may be unfamiliar with, but one that plays a fundamental role in the human body, is mitochondria. Often described as the body’s energy systems, mitochondria are essential to almost every biological process. “Everything you’re doing is relying on mitochondria,” Glen says. “Whether that’s using your muscles to kick your legs out of bed, or reach out for that cup of coffee.”

In simple terms, mitochondria produce ATP, the molecule that powers cellular activity. His research explores how longer-wavelength light beyond 700nm may influence the efficiency of this process. “Long wavelength light lubricates each point where there’s a slight bit of resistance,” he explains, describing how photons may help support electron transfer within cellular energy pathways.

While much of the science remains under investigation, Glen believes mitochondria may sit at the centre of broader questions around ageing, metabolism and human health. “The theory that sticks to the wall hardest is called the mitochondrial theory of ageing,” he says - the idea that ageing is closely linked to the gradual decline of mitochondria over time.

As mitochondria become less efficient, the body’s ability to produce energy and maintain healthy function may also deteriorate. It is, however, important not to overstate conclusions. He emphasises that this is an evolving field with many unanswered questions, and believes the relationship between light, biology and human health deserves greater attention than it currently receives.

Modern Indoor Life

Whilst humans evolved under natural daylight, modern life is very different. People now spend much more time indoors than previous generations, fundamentally changing daily exposure to natural light.

He points not only to artificial lighting, but to indoor lifestyles more broadly. Modern life increasingly takes place inside controlled environments, often with limited exposure to the full spectrum of daylight under which humans historically evolved. “We are making ourselves vulnerable because we’re living inside,” he says, “and we’re exacerbating that vulnerability with LED lighting.”

Importantly, Glen does not separate modern indoor living from lighting technology itself. Instead, he sees them as interconnected parts of a much wider environmental shift.

Beyond Circadian Lighting?

Over the past decade, the lighting industry has increasingly explored circadian rhythms and human-centric lighting - particularly the role of light timing and blue wavelengths in regulating sleep and alertness.

Glen does not see his research as contradicting that work, but rather broadening the conversation. In his opinion, it would be a mistake to think that light only does one thing.

While circadian research largely focuses on visible wavelengths associated with the body clock, Glen’s work looks further into the infrared end of the spectrum and its potential biological effects. “These are two things that run hand in hand,” he explains.

For him, the growing interest in circadian lighting reflects a wider shift towards understanding that light may influence people in multiple ways beyond visibility alone.

A Conversation Still Emerging

Glen believes researchers may now be approaching an important moment - not because all the answers exist, but because the questions themselves are beginning to change.

For decades, conversations around light have understandably focused on visibility and visual performance. Increasingly, however, researchers are exploring whether light may also influence the body in broader biological ways that remain only partially understood.

Exactly where this research may lead remains uncertain. But discussions around daylight, wavelength, and human biology are beginning to open new conversations about the relationship between people, light, and the environments they spend most of their lives in.

In Part 2, we explore what these emerging ideas could potentially mean for lighting design, architecture and the future of healthy indoor environments.