A NASA astronaut has shown how the Earth has changed over 23 years: previously, night cities from space looked yellow, but now they are blue-white. It is all due to megacities switching from sodium lamps to LED lighting to save money. Phone and laptop screens also emit blue light. In the evening, such light can suppress the production of melatonin — a hormone that helps the body prepare for sleep. This makes it harder to fall asleep.
Once, night cities glowed from orbit primarily with a warm yellow-orange light. Today, they increasingly look cold and white-blue. The reason is the mass transition of megacities from sodium lamps to LED lighting.
And this change is noticeable not only in photographs of Earth from space.
For our bodies, not only the brightness of light is important, but also its spectrum. There are special light-sensitive cells in the retina connected to our internal biological clocks. They react particularly actively to short-wavelength light — roughly in the blue-cyan part of the spectrum.
It is precisely this light that has a stronger effect on the production of melatonin — the hormone that helps the body understand in the evening that night is coming and it is time to prepare for sleep.
Therefore, the problem really isn't just with the phone.
Yes, smartphones, tablets, and laptops also emit light with a significant blue spectrum component. But around us, there are also bright LED lamps at home, street lighting, shop windows, advertising signs, office buildings, and light from the windows of neighboring houses.
As a result, in the evening, a person can literally be in an environment that, from the brain's perspective, still resembles daytime.
Cold white light is used particularly actively in modern cities because LED lamps are economical, durable, and illuminate streets well. However, it is these cold shades that typically have a stronger effect on the circadian system than warm yellow light.
At the same time, it is important to understand: a single streetlamp outside the window will not necessarily deprive you of sleep on its own. Sleep is affected by a combination of factors — brightness, duration of exposure, time of day, and the light spectrum.
But if there is bright cold light on at home in the evening, a screen in front of your eyes, and streetlamps and signs shining outside all night, the body receives several signals at once that "the day is still continuing."
And then it really can be harder to fall asleep.
It turns out to be somewhat paradoxical: cities have become more economical and technologically advanced, but the nights have become significantly brighter.
For the brain, however, darkness remains an important signal. It is the reduction in light levels in the evening that helps switch from activity mode to rest mode.
Therefore, one of the simplest ways to improve your evening lighting routine is to reduce the brightness of the lights an hour or two before bed, choose warmer bulbs, avoid keeping bright overhead lights on, and, where possible, limit the light entering the bedroom from the street.
So the phone may indeed not be the only one to blame.
Sometimes the whole city, along with it, simply forgets to turn off the day.
