What is blue light?
Visible light is more complex than you might think.
Stepping outdoors into sunlight; flipping on a wall switch in your house; turning on your computer, phone or other digital device — all of these things result in your eyes being exposed to a variety of visible (and sometimes invisible) light rays.
Most people know sunlight contains visible light rays and also invisible ultraviolet rays that can tan or burn your skin. But what many don’t know is that sunlight contains a wide range of different-colored visible light rays that contain different amounts of energy.
Sunlight contains red, orange, yellow, green and blue light rays and many shades of each of these colors. The color of individual light rays depends on their energy and wavelength. Combined, the full spectrum of colored visible light rays creates what we call “white light” or sunlight.
Digital electronic devices emit blue light.
Without getting into complicated physics, there's an inverse relationship between the wavelength of a light ray and the amount of energy it contains. Light rays that have short wavelengths have more energy and those with longer wavelengths contain less energy.
Rays on the blue end of the visible light spectrum have short wavelengths and high energy. Those on the red end of the spectrum have long wavelengths and less energy.
Invisible rays just beyond the red end of the visible light spectrum are called infrared radiation. The “warming lamps” you see in restaurants emit infrared radiation. (But these lamps also emit visible red light so people know the lamps are on! The same is true for other types of heat lamps.)
On the other end of the visible light spectrum, blue light rays with the shortest wavelengths (and highest energy) are sometimes called blue-violet or violet light. This is why the invisible rays just beyond the visible light spectrum are called ultraviolet (UV) radiation.
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The perils and benefits of UV
UV rays have higher energy than visible light rays (including blue light), which makes them capable of producing changes in the skin that create a suntan. The bulbs in tanning booths emit a controlled amount of UV radiation specifically for this reason.
But too much exposure to UV rays causes a painful sunburn — and even worse, can lead to skin cancer. These rays can also cause sunburned eyes — a condition called photokeratitis or snow blindness.
In moderation, however, UV rays have beneficial effects — such as helping the body manufacture adequate amounts of vitamin D.
