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The Dark Side Of Visible And Invisible Light

By Essilor News

Our eyes are one of the smallest organs in our bodies, yet there are more than 100 million tiny cells - called rods and cones - inside the retina alonethat are responsible for responding to light. While rods help with vision in low light, cones help us see the world in color. In fact, our eyes can visualize all colors of the rainbow through reflected light, but the colors we see are part of a very narrow band of wavelengths on the light spectrum . The question is - what can't we see?

What is Visible Light ?
Our eyes are sensitive to a narrow band of electromagnetic waves, known as the visible light spectrum . To understand how visible light is broken into various wavelengths, take a cue from Isaac Newton - shine a light through a prism. A prism separates visible white light into separate wavelengths, and each color that appears - red, orange, yellow, green, blue, and violet - is a characteristic of the distinct wavelengths.

Certain colors are seen as objects around us absorb some light and reflect the rest, depending on the properties of the object. For example, a strawberry reflects the wavelength of visible light that appears as red.

What about white and black? White is the result of a mixture of two or more colors of light. This is why visible light - or the mix of the rainbow of colors - is also referred to as white light. Black is the absence of the visible light spectrum wavelengths. Everything in a dark room appears black because there is no visible light to strike your eye as you gaze at the surrounding objects.

What is Non-Visible Light?
The human eye can only see visible light, but light comes in many other "colors" - radio, infrared, ultraviolet, X-ray, and gamma-ray - that are invisible to the naked eye.

On one end of the spectrum there is infrared light , which, while too red for humans to see, is all around us and even emitted from our bodies. Warm-blooded animals, including humans, radiate infrared light. That's why infrared cameras are helpful for thermal imaging and night vision when searching for people or animals.

On the other end of the spectrum there is X-ray light, which is too blue for humans to see. X-rays are another common light source that many of us have encountered at a doctor's office. X-rays can penetrate skin and muscles allowing doctors to look at our bones. What you might not know is that the sun also emits X-rays. Lucky for us, the Earth's atmosphere blocks X-ray light.

Non-visible light can also be found in your house, in a device that you most likely use every day - remote controls! Your remote control uses infrared light to transmit signals to the television and other electronics. While the signal is invisible to you, your television can process the light and respond.

The Benefits and Dangers of Light
Aside from helping us see, visible light is also beneficial to our bodies and overall health. Research shows that certain wavelengths of red light can penetrate the skin to reduce wrinkles and help repair skin damage; while parts of the blue light wavelength regulate the biological clock, or sleep/wake cycle, and play a role in basic functions of the human brain such as alertness, memory, emotion, and cognitive performance.

Unfortunately, not all light is safe, and particular bands of light are a hazard to our health.

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