Today’s Wonder of the Day was inspired by Jennifer. Jennifer Wonders, “why cant we see ultraviolet light?” Thanks for WONDERing with us, Jennifer!

Think of the brightest colors you’ve ever seen. Maybe you’ve stared into a crisp blue sky. Perhaps you picture bright green grass. You might even think of a beautiful sunrise or sunset

If you’ve been WONDERing with us for a while, you know where the colors you see come from. They’re made by waves of light bouncing off other objects. But would you believe there are some light waves that can’t be seen by the average human eye?

It’s true! Generally, humans can see light with wavelengths between 380 and 700 nanometers (nm). All the colors of the rainbow—from red all the way down to violet—fall within that range. But ultraviolet (UV) light has wavelengths shorter than 380 nm. That means they go undetected by the human eye.

Are you WONDERing where the name “ultraviolet” comes from? You might already know that violet light has the shortest wavelength of all the visible colors. That means it travels faster and has more energy than the other colors of light. The prefix “ultra-” means “beyond.” UV light waves move faster than violet ones. So, “ultraviolet” means this type of light is beyond violet, which is the fastest color we can see.

Just because humans can’t see UV light doesn’t mean it doesn’t affect us. Most of the UV rays are absorbed by the Earth’s atmosphere. However, those that reach us can cause sunburn and other damage. This is one reason why the ozone layer is so important. Without it, more UV light would reach the Earth’s surface.

Is UV light invisible to everyone? Actually, no. People with a condition called aphakia can see UV light waves. Those with aphakia are missing an eye lens, often due to surgery or genetics. The lack of this lens enables them to see beyond the visible spectrum of light, but it also causes blurry vision and farsightedness. 

Additionally, some animals can see UV light. Scientists have known for a long time that bees have this ability. Many birds and reptiles can, too. Until recently, experts believed that UV light was invisible to all mammals. However, a recent study found that most mammals probably can see these waves of light, including dogs, cats, and reindeer. It found that the lenses in their eyes allow UV light to pass through.

How about the other end of the spectrum of visible light? Red light has the longest wavelength commonly visible to humans. Light with longer wavelengths than red is called infrared. Scientists once believed no one could see infrared light. However, experts today think many humans can do so, especially if more than one infrared photon hits the eye at once.

 How do you think the world might look different if you could see UV light? Would you see a deeper shade of violet? Maybe it would be a whole new color altogether!

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Wonder What's Next?

Tomorrow’s Wonder of the Day pays a visit to a colorful little critter!