Are We Missing Red Light? How Modern Indoor Lighting May Be Affecting Our Mitochondria

We spend more time indoors than ever before, surrounded by artificial light. But emerging research suggests that it may not simply be how much light we receive that matters, the wavelengths within that light may matter too.

For most of human history, our primary source of light was the sun.

Sunlight contains a remarkably broad spectrum of wavelengths, extending from ultraviolet through visible light and into red and near-infrared wavelengths. Our biology evolved within this environment.

Modern life looks very different.

We work under LEDs, illuminate our homes with LEDs and spend hours looking at LED screens. At the same time, increasingly sophisticated glazing can alter the spectrum of sunlight reaching us indoors.

LED technology has brought enormous advantages in energy efficiency and longevity. But researchers are beginning to ask an intriguing question:

Has changing our light environment also changed something biologically important?

Recent research into mitochondria, metabolism and photobiomodulation suggests that red and near-infrared wavelengths may play a more significant role in human physiology than was previously appreciated.

Sunlight Is More Than Visible Light

When we think about sunlight, we tend to think about what we can see.

But visible light represents only part of the solar spectrum.

Sunlight reaching us contains wavelengths extending beyond visible red into near-infrared and infrared light. Unlike shorter wavelengths, longer wavelengths can penetrate relatively deeply into biological tissue.

Researchers at University College London and collaborating institutions have been investigating what happens when these wavelengths interact with our cells.

A 2025 study published in Scientific Reports examined the ability of longer wavelengths in sunlight to pass through the human body and produce systemic effects. The researchers reported that longer-wavelength red light could penetrate tissue and was associated with changes in mitochondrial function and ATP production.

This matters because mitochondria sit at the centre of one of the most fundamental processes in human biology: producing energy.

Why Mitochondria Matter

Almost every cell in the body requires energy.

Much of that usable cellular energy is produced by mitochondria in the form of adenosine triphosphate, or ATP.

ATP powers an extraordinary range of biological processes, from muscle contraction and cellular repair to nerve signalling and normal cellular maintenance.

Mitochondria use oxygen and nutrients, including glucose, as part of this energy-producing process.

Research into photobiomodulation (PBM) suggests that particular wavelengths of red and near-infrared light can interact with mitochondrial processes and influence cellular energy production.

This is the science that underpins much of modern red light therapy.

And researchers are now asking whether our everyday light environment could also influence these mechanisms.

The Problem With the Modern Light Spectrum

LED lighting is exceptionally efficient because it produces the wavelengths required to create visible illumination without generating large quantities of energy elsewhere in the spectrum.

From an engineering perspective, this is a major achievement.

Biologically, however, it means that the light produced by many LEDs is very different from daylight.

A 2026 study by Edward Barrett and Professor Glen Jeffery, published in Scientific Reports, compared conventional LED lighting with broader-spectrum illumination extending into longer wavelengths.

The researchers describe modern LEDs as being concentrated predominantly between approximately 350 and 650 nanometres, whereas natural daylight extends much further into infrared wavelengths.

Their study investigated whether supplementing an LED environment with broader-spectrum light could influence visual function.

After two weeks of supplemental broad-spectrum lighting, participants demonstrated improvements in colour contrast sensitivity, an effect that remained measurable for two months after the supplemental lighting was removed.

The researchers proposed mitochondrial function as an important mechanism behind these effects.

It is an intriguing finding.

It doesn't mean that LED lighting is inherently dangerous, nor does it establish that LEDs cause metabolic disease.

But it does raise a much bigger question:

Could the absence of certain wavelengths from our indoor environment matter to our biology?

Red Light and Blood Glucose: A Fascinating Human Study

One of the most interesting pieces of research comes from scientists at City, University of London and University College London.

Published in the Journal of Biophotonics in 2024, the study investigated whether stimulating mitochondria with red light could influence blood glucose.

Researchers exposed healthy participants to 670 nm red light for 15 minutes before giving them an oral glucose tolerance test.

The results were striking.

Compared with the control condition, exposure to 670 nm light was associated with a 27.7% reduction in the overall rise in blood glucose during the following two hours, alongside a 7.5% reduction in the maximum glucose spike.

The proposed explanation was increased mitochondrial activity.

If mitochondria increase their production of ATP, they require energy to do so. One potential consequence is increased glucose utilisation.

It is an elegant demonstration of something that would once have sounded rather unlikely:

Light applied to the body may influence metabolism elsewhere in the body.

However, this needs important context.

The study involved healthy participants and examined an acute response to a glucose challenge. It does not demonstrate that red light therapy treats diabetes, nor does it establish what repeated exposure would mean for long-term metabolic health.

Further research and larger clinical trials are needed.

But it provides compelling evidence that light and metabolism may be more closely connected than we once assumed.

Light Doesn't Necessarily Act Only Where It Shines

Perhaps one of the most fascinating developments in this field is evidence suggesting that the biological effects of red and near-infrared light may not be entirely local.

In other words, light doesn't necessarily have to reach a particular organ directly to influence it.

Research published in Scientific Reports in 2025 explored this systemic effect using vision as a model.

The researchers investigated whether longer wavelengths passing through other areas of the body could influence retinal function. Their findings supported the possibility that mitochondrial responses to light can generate signals that affect tissues elsewhere.

Exactly how these systemic effects occur is still being investigated.

But if confirmed through further research, the implications for photobiomodulation could be significant.

Have We Changed Our Light Environment Too Quickly?

This is where the science becomes particularly thought-provoking.

Humans evolved outdoors under a broad solar spectrum.

Yet within only a tiny fraction of our evolutionary history, many of us have moved into environments dominated by artificial illumination.

The transition to LED lighting has accelerated this change dramatically.

Professor Glen Jeffery and other researchers working in this area have raised the possibility that reducing our exposure to longer red and near-infrared wavelengths could have physiological consequences.

Research groups elsewhere are also examining the relationship between the indoor environment and metabolism.

At Maastricht University, for example, researchers in thermophysiology and metabolism are studying how environmental factors including light and temperature interact with human physiology and metabolic health.

This is still a developing field.

There is not currently enough evidence to conclude that modern indoor lighting causes metabolic disorders or that simply adding red light to our homes will prevent them.

But the emerging research challenges a long-held assumption that indoor lighting is biologically neutral.

Light may be doing considerably more than helping us see.

Where Does Red Light Therapy Fit?

Red light therapy, more formally known as photobiomodulation, deliberately delivers specific wavelengths of red and/or near-infrared light to the body.

Depending on the device and intended application, these wavelengths commonly sit within regions of the spectrum being investigated for their interaction with mitochondrial and cellular processes.

This is fundamentally different from simply installing a red-coloured bulb.

Therapeutic devices are designed to deliver defined wavelengths at controlled intensities and doses.

Research into photobiomodulation now spans areas including cellular energy production, exercise and recovery, skin health, inflammation and other physiological processes.

The strength of evidence varies considerably between applications, and research is continuing.

What makes the emerging research into our everyday light environment so interesting is that it places photobiomodulation within a much wider biological context.

Rather than asking only:

“What can red light therapy do?”

Researchers are beginning to ask:

“What role has red and near-infrared light always played in human biology?”

That may prove to be the more important question.

Perhaps We Need to Think Differently About Light

We carefully consider what we eat, how much we exercise and how well we sleep.

Increasingly, we monitor temperature, air quality and other aspects of our environment.

Light has traditionally been considered primarily in terms of vision and circadian rhythm.

The emerging research into mitochondria suggests the picture could be considerably broader.

Our cells evolved in an environment filled with wavelengths that are now substantially reduced in many indoor spaces. Whether this change is clinically important, and how much exposure to different wavelengths humans actually require, remains to be established.

But the research gives us another reason to value something remarkably simple:

natural daylight.

And it gives scientists an increasingly compelling reason to continue investigating red and near-infrared light, mitochondria and photobiomodulation.

The relationship between light and human health may turn out to be far more fundamental than simply what allows us to see.

The Research

Powner MB, Jeffery G. (2024)
Light stimulation of mitochondria reduces blood glucose levels.
Journal of Biophotonics, 17(5), e202300521.
DOI: 10.1002/jbio.202300521

Jeffery G, Fosbury R, Barrett E, Hogg C, Rodriguez Carmona M, Powner MB. (2025)
Longer wavelengths in sunlight pass through the human body and have a systemic impact which improves vision.
Scientific Reports, 15, 24435.
DOI: 10.1038/s41598-025-09785-3

Barrett EM, Jeffery G. (2026)
LED lighting (350–650 nm) undermines human visual performance unless supplemented by wider spectra (400–1500 nm+) like daylight.
Scientific Reports, 16, 3061.

Further reading

This article was inspired in part by Graham Lawton's feature in New Scientist, “The shock revelation that light bulbs are wrecking your metabolism”, published in August 2026.

Important note

Research into photobiomodulation and the biological effects of different light wavelengths is developing rapidly. Findings discussed here should not be interpreted as evidence that red light therapy can diagnose, prevent or treat metabolic disease. Red light therapy should not replace medical assessment or treatment.