Panward Cervone

With review and contributions from Ophthalmologist Ernest Bhend, MD (Fort Mill)

Humans can see a wide variety of colors along the visible light spectrum. But the spectrum of light goes beyond red and violet, and these rays are invisible to the human eye. Today we’ll talk about infrared and ultraviolet rays, and why we can’t see them.

Before we talk about light we can’t see, let’s talk about what we can. The visible light spectrum is a section of the electromagnetic spectrum that the human eye can detect. The cones in our eyes act as receivers for radiation with wavelengths from 380 to 700 nanometers. This includes red, orange, yellow, green, blue, purple, and all the colors in between.

Infrared waves are a portion of the light spectrum that follows red. They have longer wavelengths than visible light, ranging from 700 nanometers to one millimeter. This renders them invisible to humans in almost all conditions. There are limited situations, though, when humans can see infrared light. If concentrated bursts hit the eye, they can be perceived as a flash of green light.

Infrared lights are commonly used in remote controls. They are also used in thermal imaging cameras or night vision goggles because infrared can be detected as heat. If you have ever seen the multicolored images from a thermal imaging camera, you are seeing these devices interpret infrared waves in a way that humans can see them.

Infrared light is often used in astronomy because it can perceive objects that would be too faint to detect in visible light.

While it is difficult for humans to see infrared light, some animals, like snakes and bedbugs, can detect it.

Ultraviolet light is a type of electromagnetic radiation that precedes the color violet in the light spectrum. The sun is the best-known source of ultraviolet rays.

Ultraviolet light has shorter wavelengths than visible light, with lengths of 10 to 400 nanometers. While invisible to humans, as with infrared light we can see the effects. For example, if you have ever watched a blacklight change the colors of a poster or seen a bank teller use one to detect counterfeit money, you are watching the effects of ultraviolet light. And, while you can’t see the rays themselves, ultraviolet rays are what cause people’s skin to tan in the sun.

Like infrared light, some animals can see ultraviolet rays. Bees, for example, can see this portion of the spectrum.

Even though you can’t see them, infrared and ultraviolet rays can still cause injury.

“Both infrared and ultraviolet light can damage the light receptors in the eye,” CEENTA Ophthalmologist Ernest Bhend, MD, said. “Be sure to wear proper eye protection to protect your eyes from this damage, especially good UV-blocking sunglasses if you are out in the bright sunlight.”

While infrared and ultraviolet light are invisible to the human eye, there are still plenty of things people can see. Don’t hesitate to visit a CEENTA eye doctor to make sure you can view all of them as well as possible.

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