Light perception extends far beyond just vision. Light is an amalgam of other components apart from the visible spectrum. Heat sensation is possible due to light’s presence, body’s Vitamin D synthesis relies entirely on the UV rays, light sets a morning alarm to wake your body and is one of the main participants in how the body manages its internal timing. It is the answer to why you get dark circles working all night on your PC or why you get tanned or sun-burnt. So, there’s pretty much light our body uses every day.
Why Screens Are Bad For Our Eyes: Melatonin Production Depends On The Wavelength
If you refer to the above experiment you will find that melatonin production is ceased or suppressed after the light’s wavelength drops down a certain value (approximately 530nm). This is the reason why looking at mobile and TV screens for long can make you hyperactive, suppressing the melatonin secretion (because they emit high amounts of blue light). This is also the reason why workers disturb their sleeping cycles during night shifts.
At the same time, lights with longer wavelengths don’t really affect melatonin secretion but can actually help you have a sound sleep.
Seeing without eyes – the unexpected world of nonvisual photoreception
Intrinsically photosensitive retinal ganglion cells
Why Do People In Different Parts Of The World Have Different Skin Colours?
Why Do We Get Dark Circles?
The skin under our eyes is very thin and sensitive. When exposed to a light coming from a screen or even to excessive sunlight, this skin can develop melanin normally as the entire body does, but it usually appears darker than usual as due to its thin structure the blood vessels are much closer to the surface and the melanin is visible through the vessels clearly. And thin structures require more protection, so more melanin is produced. (See here for details)