![]() ![]() Some studies suggest a link between exposure to light at night, such as working the night shift, to diabetes, heart disease, and obesity. Charles Czeisler of Harvard Medical School showed, in 1981, that daylight keeps a person's internal clock aligned with the environment. The circadian rhythm of people who stay up late is slightly longer, while the rhythms of earlier birds fall short of 24 hours. Light and sleepĮveryone has slightly different circadian rhythms, but the average length is 24 and one-quarter hours. And the proliferation of electronics with screens, as well as energy-efficient lighting, is increasing our exposure to blue wavelengths, especially after sundown. Blue wavelengths-which are beneficial during daylight hours because they boost attention, reaction times, and mood-seem to be the most disruptive at night. Not all colors of light have the same effect. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity. At night, light throws the body's biological clock-the circadian rhythm-out of whack. Now, in much of the world, evenings are illuminated, and we take our easy access to all those lumens pretty much for granted.īut we may be paying a price for basking in all that light. Until the advent of artificial lighting, the sun was the major source of lighting, and people spent their evenings in (relative) darkness. As a result of this increased amount of scattering, the dominance of blue light is decreased and so we see an increased amount of white light.What is blue light? The effect blue light has on your sleep and more.Īlthough it is environmentally friendly, blue light can affect your sleep and potentially cause disease. The Earth's surface also plays a role in scattering and reflecting this light. This is because the light from the horizon has had further to travel through the air and so has been scattered and rescattered. You might also notice that the sky tends to be most vibrant overhead and fades to pale as it reaches the horizon. Why does the blue fade towards the horizon? The blue light that gives the sky its colour, is sufficiently bright to make all the stars that we see at night disappear since the light they emit is much dimmer. ![]() This is because there isn't as much violet in sunlight to start with, and our eyes are much more sensitive to blue. You might wonder why the sky doesn't actually look purple since the violet light is scattered even more strongly than blue. Shorter wavelengths (violet and blue) are scattered the most strongly, so more of the blue light is scattered towards our eyes than the other colours. This effect is called Rayleigh scattering, named after Lord Rayleigh who first discovered it. Because these molecules are much smaller than the wavelength of visible light, the amount of scattering depends on the wavelength. When the Sun's light reaches the Earth's atmosphere it is scattered, or deflected, by the tiny molecules of gas (mostly nitrogen and oxygen) in the air. At one end of the spectrum is red light which has the longest wavelength and at the other is blue and violet lights which have a much shorter wavelength. We can think of light as being a wave of energy, and different colours all have a different wavelength. Although light from the Sun looks white, it is really made up of a spectrum of many different colours, as we can see when they are spread out in a rainbow. To understand why the sky is blue, we first need to understand a little bit about light. ![]()
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