Light & your cells
Around half of the energy in sunlight arrives as invisible infrared. A growing body of research suggests the tiny engines inside our cells were built to use it.
THE BIG IDEA
Sunlight services the engine
Food is the fuel, but it’s your mitochondria, tiny engines inside almost every cell, that turn it into usable energy. Astrophysicist Bob Fosbury compares sunlight to the oil and servicing that keep a car running well for a lifetime. Infrared light doesn’t add fuel. Instead, it seems to help electrons pass through the mitochondria’s chain of ‘locks’ more easily, so your cells make energy with less wear and tear. Without it, as in our LED-lit indoor lives, the engine still runs, just not as smoothly.
HOW IT WORKS
From the Sun to your cells, in three steps
1
Sunlight arrives rich in infrared
Counted in photons rather than energy, sunlight peaks in the near-infrared, at around 1,600 nanometres, thanks to a quirk of the Sun’s own atmosphere.
2
It travels deep into the body
These long wavelengths pass through skin and clothing and scatter through our tissues, rather than stopping at the surface like visible light.
3
Mitochondria run more smoothly
The energy of these photons closely matches the barriers electrons must cross inside mitochondria, nudging them over with less damage along the way.
WHAT THE SCIENCE SAYS
The numbers behind the idea
From the paper ‘Editing the Sun: how indoor light lost touch with biology’ by Bob Fosbury, Roger Seheult, Scott Zimmerman and Glen Jeffery.
0.7 vs 0.75 eV
The average energy barrier in mitochondria, measured across plants, fungi and animals, sits right beside the energy of sunlight’s most plentiful photons.
~100 watts
Roughly how much infrared from the Sun a person intercepts, comparable to or above the body’s resting metabolic rate.
3 minutes
One three-minute dose of deep red light in the morning improved colour vision by around 17% for up to a week, in a small UCL study.
1 bulb
When one bulb with an infrared component was added to an LED-lit office by mistake, the vision of everyone working there improved, Glen Jeffery recalls.
FROM THE PODCAST
In their own words
Bob Fosbury
Astrophysicist, European Southern Observatory
Prof. Glen Jeffery
UCL Institute of Ophthalmology
Dr Roger Seheult
Loma Linda University
WHAT YOU CAN DO
Give your cells more daylight
Get outside every day
A walk in the park beats any red light gadget, says Glen Jeffery: you get infrared and exercise, and your mitochondria love both.
Catch the morning
In Glen Jeffery’s studies, red light improved vision when given in the morning, but not in the afternoon.
Seek out green spaces
In strong sun, touch a leaf and then a brick wall. The wall is warm because it absorbs infrared; the leaf is cool because it reflects it back at you.
Rethink indoor lighting
Where you can, add a broad-spectrum lamp, such as incandescent or halogen, alongside your LEDs.
Put it into practice
Find your morning sun
Use Shadowmap to see exactly when sunlight reaches your home, your garden or the nearest spot to watch the sunrise, on any day of the year.
KEEP READING
More health guides
Explore how light shapes other parts of your health, from your cells to your sleep.
Light & mood
Why bright days and dark nights are linked to a lower risk of depression.
Read the guide →
Body clock & sleep
How morning light, dark evenings and a strong daily rhythm keep your body in sync.
Read the guide →
Sun, skin & safety
What the research says about melanin, building up exposure gradually and never burning.
Read the guide →
Sources & further listening
Fosbury R., Seheult R., Zimmerman S. & Jeffery G., ‘Editing the Sun: how indoor light lost touch with biology’ (2026). Sunlight Matters podcast episodes with Bob Fosbury, Glen Jeffery, Roger Seheult, Scott Zimmerman and Jonathan Jarecki. This page is general information, not medical advice.
