It’s common knowledge that humans have largely become an indoor species, spending upwards of 90% of their time inside. However, few have given much thought to the ways this shift toward indoor living might be affecting our health.
That may be about to change. A growing number of scientists believe the indoor environments we’ve built for ourselves are having some unintended consequences – with serious implications for public health.
Some seemingly innocuous developments of the last two decades may be at the root of some of the biggest health risks of lives spent mostly indoors. Mounting research suggests that the light environments we’ve created in the last 15 years could be playing a significant role in the soaring rates of chronic disease.
One especially detrimental effect of all the time we spend inside: How little full-spectrum light most of us now get.
The narrowing of our light environment
Sunlight – the light all life on Earth evolved under – contains a wide range of wavelengths, including the visible light spectrum, shorter ultraviolet rays, and longer infrared rays. The wavelengths human vision can perceive fall in the range of 380 to 740 nanometers, while the infrared spectrum ranges from about 750 to 1 million nanometers.
In their efforts to make lighting more energy-efficient, lighting engineers logically sought to produce as much light as possible using the least amount of electricity. This meant designing bulbs that produced abundant visible light and didn’t waste energy on wavelengths we can’t see.
According to Glen Jeffery, Professor of Neuroscience at University College London, in contrast to the full spectrum of light found in sunshine or even the broad spectrum emitted by incandescent bulbs, LED bulbs emit a far narrower band of wavelengths. They have an especially prominent output in the range of 420 to 440nm, which Jeffery describes as “really problematic” for their impact on health. Others have called the dominance of these wavelengths “toxic.”
Further limiting our exposure to full-spectrum light, infrared-filtering films are now routinely applied to modern windows to limit heat gain and reduce the energy needed for cooling. While this innovation saves significant amounts of electricity for air conditioning, it also means that the spaces so many of us live and work in offer a far more restricted range of light than they did just a few decades ago.
Are LED lights bad for you? Biology and the light spectrum
How is something as seemingly straightforward as indoor lighting affecting human health? Scientists in a variety of disciplines have only recently begun seeking answers to this question.
Researchers posit that human physiology, which evolved under the full spectrum of wavelengths produced by the sun, depends on receiving this broader range of light exposure. Research suggests that molecules in our cells absorb infrared wavelengths, influencing numerous biological and chemical processes.
One of the most-studied ways infrared light affects bodily processes is via our mitochondria. These critical organelles, often referred to “powerhouses of the cells,” are responsible for producing energy and regulating many physiological processes, including our immune response, death and cleanup of damaged cells, hormone production and many other vital functions. Research has found that the trillions of mitochondria found throughout the body communicate with each other to direct these processes.
Because of their central role in so many cellular processes, researchers believe that mitochondrial dysfunction affects the development of numerous chronic conditions, including heart disease, metabolic disorders and neurological issues. Mitochondria are thought to play a significant role in the aging process as well.
Jeffery has been at the forefront of research exploring how different wavelengths of light affect mitochondrial health. He’s found that under the wavelengths of light that predominate in our now ubiquitous LED bulbs, mitochondrial health suffers, while infrared wavelengths improve their function significantly.
Your body on LED lighting
Jeffery’s ongoing work adds to a growing body of research showing that animals – humans included – don’t respond well to light wavelengths in the range produced by LEDs.
His experiments with animals have shown that restricting exposure to wavelengths in the 420–440 nanometer range dominant in LEDs slows down mitochondria and harms numerous aspects of health. Insects become disoriented when exposed to these wavelengths for short periods, and when kept under them for longer, they die prematurely.
Animal experiments have shown that mice restricted to light environments in the range of 420–440 nm show rapid weight gain. Researchers speculate that increasing rates of metabolic disorders may be linked to our insufficient exposure to the broader spectrum of light.
Studies suggest that blue wavelengths of light like those emitted by our devices and LEDs may damage eye health, increasing risk of macular degeneration and cataracts. Additional research has found that blue light from devices can accelerate skin aging.
Robert Fosbury, an astrophysicist with an interest in the effect of light on biology, contends that “We made a huge unconscious mistake when we decided to change the lighting in the built environment.” In his collaborations with scientists in diverse disciplines, Fosbury reports, “What we’ve realized increasingly is that the removal of non-visible light from indoor lighting has been a catastrophe of the first order.”
Fosbury likens what he views as “infrared starvation” caused by indoor environments devoid of infrared wavelengths to scurvy, a disease caused by a vital missing nutrient. In this case, the nutrient is infrared light.
“We believe this is one of the main contributors to the gradual peaking in decline in public health that we’ve noticed over in the last decade or so,” he explains. “The increase in type 2 diabetes and obesity, in all the diseases of aging, and many of these things can be attributed to mitochondrial dysfunction.”
Jeffery notes that the effects of limiting one’s exposure to this narrow range of light build up over time. “All the damaging things that come from blue light come from longer term blue light exposure,” he says. “If I want to undermine your mitochondria with blue light, I have to expose them for quite a long time consistently.”
Bringing back balance
Jeffery’s experiments adding back in the wavelengths of light missing from LEDs suggest that introducing infrared and near infrared wavelengths have beneficial impacts on mitochondria and “can improve system function from fly through to human.”
In human studies, he’s found that longer wavelengths stimulate mitochondrial metabolism and have a beneficial effect on blood sugar. Additional experiments have revealed that sessions of exposure to infrared help improve retinal function.
One recent experiment involved workers in an office lit by LEDs with no sources of natural light. Half of the workers had a 60-watt incandescent lamp added to their work space, while the other half did not. After two weeks, Jeffery’s team measured the visual acuity of both groups and found a 25% improvement in the vision of the workers with the incandescent bulbs compared to the control group. This improvement lasted several weeks after the incandescents were removed, which study authors believe points to the beneficial impact of broader spectrum light on the overall health of mitochondria in these workers’ eyes.
Other researchers have found that infrared light exposure can improve neurological health and are exploring it as a therapy for Parkinson’s, dementia and traumatic brain injuries.
A 2024 study monitored two groups of college students while they performed “cognitively demanding tasks,” one group under standard LED lights, and one group under bulbs with added infrared wavelengths. Researchers found beneficial effects on heart rate variability and subjects’ feelings of pleasure during the tasks, supporting other research suggesting that “lighting influences humans at a psychological and physiological level, with implications for health and well-being that need to be balanced with energy-saving considerations.”
Broadening your spectrum
While no one has definitive data about exactly how much broad-spectrum or infrared light exposure is necessary to support human health, researchers agree that most modern humans would be better served by getting a great deal more.
How to do that? Jeffery suggests spending time outside when you can and increasing the amount of infrared light you get indoors. “People can counter the effects of blue light,” he says, “by bringing more long-wave light into their environment.” He recommends using incandescent bulbs where you can and suggests adding small lamps with incandescents to spaces lit by LEDs or fluorescent lights to help you get a better balance of wavelengths.
When your windows were made can also affect which wavelengths of light you’re exposed to. If the buildings where you live and work were built before 2010, your windows aren’t as likely to have coatings with infrared filters, which take out 80-90% of infrared light, Jeffery explains. In contrast, he says, “Lots of infrared will come through a normal sheet of glass.” If a window feels hot when sunlight hits it, Jeffery reports, it’s letting in those infrared wavelengths, and spending time in rooms with such windows will help you get more beneficial infrared light exposure.
Jeffery advises spending time outdoors whenever possible, whether that’s walking to work or taking your lunch break in the park. “It doesn’t take a lot to add correction to the problem,” he counsels.
Fosbury points out that you don’t need to bake in the sun to get infrared exposure. While clothing shields you from UV rays, infrared light penetrates cloth. Further, he notes, the leaves of trees are extremely effective at reflecting infrared wavelengths. “Sitting in the shadow of a sun-illuminated tree is about the healthiest place you could be for metabolic/mitochondrial health,” he says. One more reason to seek out the benefits of time in nature, whether you try forest bathing or take more meals outdoors.
Though you’ll see countless red light therapy products for sale online, Jeffery warns that most don’t emit the long wavelengths we’re missing. After testing numerous devices sold online, he’s found just a few actually produce these infrared wavelengths. It’s much more certain you’ll achieve a healthier balance of light from an incandescent or halogen lamp attached to a dimmer switch, which lets you regulate the energy these less-efficient bulbs use and significantly prolongs their life.
Though Jeffery calls these measures “sticking plasters” (British for band aids), he says they help. To better address this pervasive problem, he and his colleagues are working with architects and lighting experts to innovate ways we can balance energy efficiency with our need for broader spectrum light. He predicts the future of lighting will look very different as research continues to uncover the negative health effects of restricting the wavelengths we’re exposed to and engineers design lighting that both saves energy and protects human health.
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