The shock revelation that light bulbs are wrecking your metabolism | New Scientist

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Red light is missing from much of our lives<br>Emanuel Santos

Take a flashlight – the one on your phone will do – turn it on and place the pad of your index finger over the bulb. See that red glow? You might think it’s something to do with blood, but you’d be wrong. It’s photons of red light bouncing around inside your finger, looking for somewhere to land.

This simple experiment is a doorway to one of the most profound and surprising biological discoveries of recent years. “Light is a nutrient,” says Bob Fosbury, who was an astrophysicist at the European Southern Observatory before he turned his attention to the biology of light. That’s obviously true for plants, which use light to make carbohydrates. But it turns out it’s also true for animals and fungi, all of which exploit light in a hitherto unappreciated way. All living organisms – including us – are solar-powered.

Sunlight has long been understood to be critical to life on Earth. But the fact that light is also used to oil the wheels of metabolism is only just, er, coming to light. Long wavelengths, which come from red and infrared (IR) light, are particularly beneficial for creating energy, and are readily available from sources including sunlight and incandescent bulbs.

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But changes in lighting intended to help save energy have inadvertently deprived us from this crucial supply. The irony is that just as we have discovered the benefit of red light, we are unintentionally starving ourselves of it.

Read more<br>A fresh understanding of tiredness reveals how to get your energy back

How modern bulbs starved us of red light

The story begins in the early 2000s with the widespread adoption of two now-ubiquitous energy efficiency technologies. The first was the light-emitting diode (LED), which largely replaced energy-guzzling incandescent bulbs. Although this change helped conserve energy, it had other unforeseen consequences. The second was window glass that filters out IR, designed to prevent heat leaking into or out of buildings. Together, these dramatically narrowed the spectrum of light we are exposed to indoors, an environment where most humans spend up to 90 per cent of their time. “We lost about 95 per cent of the spectrum,” says neuroscientist Glen Jeffery at University College London. “Suddenly, without warning, boom, the long wavelengths go. And that’s a problem.”

For the vast majority of human existence, those long wavelengths of light were unavoidable. Daylight is rich in visible red light, which has wavelengths of about 650 to 750 nanometres. It also emits vast and invisible (to us, at least) quantities of IR, which extends out to about 2500 nanometres.

People who spend much of the day outside are naturally exposed to these long wavelengths, even when fully clothed. When long-wavelength light hits a human body, it sails through clothing and penetrates deep into tissues (short-wavelength light such as UV, in contrast, is absorbed by clothing, which is why covering up helps prevent sunburn). Red and IR are also abundant in moonlight and in the glow of a campfire. Indoor light, too, used to be full of these wavelengths, either from sunlight streaming through windows or light sources such as open fires, candles and oil and gas lamps. The invention of the electric light didn’t change that, as the spectrum of an incandescent light bulb closely matches that of the sun.

But the adoption of energy-efficient lighting and windows robbed us of longer parts of the spectrum. Glass that filters out IR obviously blocks that portion of sunlight, and while LEDs throw out a lot of visible light, they produce nothing beyond about 750 nm. “LEDs are completely dark in the infrared,” says Fosbury. Scott Zimmerman, founder of the lighting company Silas Inc. in New Jersey who collaborates with Fosbury and Jeffery, calls LED light “ultra-processed”, an analogy with ultra-processed food. The combined effect of ultra-processed light and modern glass means that the average human today receives much less long-wavelength light than their ancestors did.

Campfires, as well as candles and incandescent bulbs, emit red light<br>ClassicStock / Alamy Stock Photo

At the same time, conditions such as obesity, type 2 diabetes, dementia and early-onset cancers are on the march. The usual suspects for this are poor diet and lack of exercise. But according to Fosbury, Jeffery and others, these are only a piece of the puzzle; another reason, perhaps the principal one, is red-light deprivation. “There’s not a single cause, but I do increasingly think that light is the most fundamental and dominant one,” says Fosbury. “And it’s...