You replaced the old bulbs. Your electric bill went down. The new lights last for years.
It sounds like an easy win.
But researchers are raising a troubling question: Did making our lighting more efficient remove something our bodies need?
University College London neuroscientist Professor Glen Jeffery is sounding a particularly strong alarm. He has compared LED lighting to “the new asbestos” and called it a “clear and present public health emergency.”
His concern reaches beyond tired eyes or trouble sleeping…
He and colleague Bob Fosbury argue that spending much of our lives under LED lighting, with little natural daylight, could undermine cellular energy production and contribute to metabolic problems, including diabetes.
Quick answer
Researchers warn that conventional LED lighting’s restricted spectrum could impair mitochondrial function, affecting metabolism and healthy aging. Animal experiments have revealed damaging effects from short blue wavelengths, while human studies have found improvements in blood sugar responses and vision when longer wavelengths are added. Long-term human studies have yet to establish the broader disease risks the researchers warn about.
Their most accessible recommendation: Make outdoor daylight a regular part of your day.
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Why researchers are concerned about LED lighting
Mitochondria turn the fuel from food into ATP, the energy that keeps your cells working. Their output declines with aging and illness.
But these tiny energy generators also respond to light — and different wavelengths can have different effects.
Certain longer wavelengths, spanning deep red and near-infrared, can increase mitochondrial energy production. Short blue wavelengths have produced damaging effects in animal experiments.
Sunlight delivers a broad spectrum containing both. Conventional white LEDs provide a narrower spectrum, with little or no near-infrared.
Fosbury, an astrophysicist and honorary professor at UCL’s Institute of Ophthalmology, describes LED-dominated indoor environments as “infrared darkness.” He argues that we have removed wavelengths that help keep the body’s metabolic machinery running.
That matters because mitochondrial changes may affect more than the tissue directly exposed to light. The researchers point to changes in cellular signaling that can carry those effects throughout the body.
The health concerns researchers are raising
Their concerns include:
- Impaired mitochondrial function: Reduced cellular energy production could affect tissues throughout the body.
- Disrupted metabolism and diabetes risk: Jeffery warns that prolonged exposure to blue-heavy lighting without balancing longer wavelengths could disrupt blood sugar regulation and undermine healthy lifespan.
- Weight gain, reduced activity and fatty liver: Jeffery reports these effects in mice exposed to LED lighting, alongside difficulty using glucose normally.
- Reduced visual performance: Their human workplace experiment found significant improvement in color contrast sensitivity after broader-spectrum lighting was introduced.
- Greater vulnerability with aging or illness: The researchers identify older adults and debilitated patients as groups of particular concern because mitochondrial function may already be compromised.
These warnings draw on a series of experiments investigating both sides of the issue: what short wavelengths can disrupt and what longer wavelengths can restore.
What the experiments reveal about light and metabolism
Some of the evidence behind the warning comes from animal research.
In a fruit-fly study published in PLOS ONE, researchers tested a specific wavelength of violet-blue light within the short-wavelength range emitted by conventional white LEDs. Repeated exposure reduced mitochondrial enzyme activity, while a longer exposure reduced cellular energy production and mobility.
Those findings help explain the researchers’ concern about cellular harm. But could changing light exposure also produce a measurable metabolic effect in people?
A 2024 study published in the Journal of Biophotonics tested that question using red light.
Researchers recruited 30 healthy adults. Half received 15 minutes of red light on their backs before a glucose tolerance test, which measures how the body handles a sugary drink. The others underwent the same procedure without the light being switched on.
The red-light intervention reduced the rise in blood glucose over the following two hours by 27.7%. Maximum glucose peaks fell by 7.5% in comparison with the same participants’ earlier tests.
The researchers proposed that increased mitochondrial activity raises glucose demand, helping remove it from the bloodstream.
This experiment involved healthy volunteers and a specific light treatment. It demonstrated a connection between light exposure and glucose regulation; it did not test whether changing household lighting prevents or treats diabetes.
Nevertheless, Jeffery sees the findings as a warning about what prolonged exposure to an unbalanced light spectrum could mean for metabolic health as we age.
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What happened when researchers restored the missing wavelengths?
The researchers’ concerns gained further support from a human workplace study published in January 2026 in Scientific Reports.
Jeffery and fellow UCL researcher Edward Barrett tested a practical question: Could adding the broader spectrum missing from conventional LED lighting produce measurable improvements in people?
The study involved 22 healthy adults aged 23–65. Eleven worked under LED lighting supplemented with incandescent tungsten lamps, which supplied longer wavelengths, including infrared. Eleven controls continued working under similar LED lighting without the added lamps.
After just two weeks, color contrast sensitivity improved by approximately 25% in the supplemented group. The control group showed no significant change. The improvements persisted at follow-up testing after the lamps were removed.
The significance goes beyond simply finding that one kind of lighting improved vision. Adding wavelengths largely absent from the participants’ everyday lighting improved how their visual systems functioned.
The study measured vision rather than diabetes, liver health or other long-term outcomes. But it provides human evidence supporting the researchers’ central concern: The spectrum of light surrounding us can affect biological function—and restoring missing wavelengths can make a measurable difference.
How to bring daylight back into your routine
The most accessible starting point is to consider how much of your day happens indoors, especially as shorter days make it easier to miss daylight altogether.
Attach outdoor time to something you already do: Take your morning coffee outside, walk during a lunch break or spend part of the evening on the porch while daylight remains.
Jeffery recommends outdoor exposure, particularly in the morning and evening, while avoiding excessive ultraviolet exposure. Fosbury also points to the near-infrared reflected by tree leaves, making time beneath trees another way to experience these wavelengths.
Jeffery suggests adding an incandescent or halogen source to LED-lit rooms where appropriate to restore some of the missing wavelengths.
Saving energy makes sense. But the researchers are raising a question that belongs in the conversation: Could lower electric bills come at the expense of our health? Their findings give us reason to look beyond what a bulb saves — and consider what our bodies may be missing. Making daylight part of your daily routine is a practical place to start.
Sources:
LED lighting (350–650nm) undermines human visual performance unless supplemented by wider spectra (400–1500nm+) like daylight — Scientific Reports
Light stimulation of mitochondria reduces blood glucose levels — Journal of Biophotonics
Red light can reduce blood glucose levels — University College London
Mitochondria are specifically vulnerable to 420nm light in drosophila which undermines their function and is associated with reduced fly mobility — PLOS ONE
“The new asbestos”: UCL researchers warn LED lighting may be damaging our health — The European, researcher interview
Are LED lights bad for us? Study claims they’re “new asbestos” — Talker News
FAQ: About LED lighting and health
They argue that its restricted spectrum, particularly the lack of near-infrared, can impair mitochondrial function.
Jeffery warns that prolonged exposure could disrupt glucose regulation. A human experiment found that adding specific red light reduced the glucose response.
Long-term human studies have not established that link. Diabetes is among the broader risks the researchers warn about.
Adding incandescent lighting improved color contrast sensitivity by approximately 25 percent in the intervention group.
Spend more time outdoors in natural daylight, particularly in the morning and evening, while avoiding excessive UV exposure.
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