Can you see heat? Can you spy what makes your skin fry? How about the energy that makes plants grow? Light has many parts that you might not be able to see with your eyes, but they still change the world around you. What happens when you put your hand out and feel the sunlight? Do you feel a tingle of warmth? Does it make you feel more awake? Let's look at the parts of light that go beyond what we can see.
Light moves through space like waves across the ocean, swelling up and down. When they hit something, they are like waves crashing on the beach, splash, splash, splash. If you look at each color of the rainbow as a light wave, you will see that the red waves are long. There is a lot of space between the swells, which means they will not hit as often. This also means red waves do not have a lot of energy. Each color that comes after "" orange, yellow, green, blue "" gets shorter and shorter, hitting more and more often, until you get to violet waves. These are the shortest and hit the beach often. They have a lot of energy! The parts of light we cannot see are even shorter than these waves. They are small enough to go through your skin! UV or ultraviolet light is light with waves that are smaller than violet light and have more energy too; we can feel them as heat, and they can even go through our cells and hurt them!
That is going to hurt.
QuinnHK at English Wikipedia, Public domain, via Wikimedia Commons
Have you ever had a nice tan? How about a bad burn from staying outside for too long? You can thank UV light for both. When you go out in the sun, a few of the light waves you cannot see can hurt your skin. Your skin can protect itself by turning darker, but it's always smart to put on sunscreen. Ultraviolet light can do good things, too. Have you ever walked through a haunted house where everything glows with a dark purple light? Another name for UV light is black light, and it can make white things like your teeth glow in the dark. So the next time you're by a black light, smile! It will look like your mouth is floating in the air by itself!
Speaking of haunted houses, let's look at some skeletons! Most cameras use light that we can see to take pictures. There are also cameras that use the parts of light you cannot see to take pictures of what is under your skin! This might not be good for family pictures . . . a picture of skeletons would be kind of strange. These cool photos are used by doctors to help you feel better or fix a broken arm. These cameras use a kind of light that you have may have heard of: x-rays.
You look like you've just seen a ghost.
X-rays are a type of light wave that is so small it can pass right through your skin and muscles but not bones or metal. If you get into a bad crash on your bike and hurt your arm, a doctor will use x-rays to see if one of your bones is broken. X-rays can damage your cells, so your doctor will lay a lead bib on your chest. This is not to keep you from spilling applesauce on yourself but to keep the x-rays from harming your other body parts while they take pictures of your arm. You will be able to see your arm without skin and muscle on a black and blue, floppy, clear picture that the doctor must hold up to the light. X-rays are also used at the airport where guards use them to look inside your bag without opening it to see if there are any metal weapons inside.
So far we have talked about parts of light that have more energy than what we can see, but the next type has the most energy. This is a kind of light that can hurt us. Gamma rays are one of the smallest parts of light, and they carry a lot of energy. They are so powerful that they can move through almost anything. Only thick stone and lead can stop them. So how high energy are these rays? You have probably heard of atomic bombs: weapons that make a very, very big explosion, wiping out everything around them. That isn't the end of their destruction. Gamma rays will move from the heat, causing cell damage to anything and everything they touch. These rays are so small and powerful, they can even damage your DNA! Bombs are a serious matter. Even after they explode.
Even though they can cause a lot of damage, we have found ways to use gamma rays for good. Can you think of what for? Let's say someone gets a terrible sickness like cancer. Doctors can use gamma rays to kill the sick parts on their body. The rays can move through skin and muscle to get to the unhealthy parts. The sick person can get better a lot faster.
Light may let us see everything that's around us. But there's a big part of light waves that do many other things, too. Sure, it can burn our skin or cause big explosions. But, it also tans our skin, shows us our bones, even fights sickness. Light has many more uses than just chasing away the dark.
References:
How Things Work. "Skin Damage and Sunburn" Discovery, 2010. <http://health.howstuffworks.com/skin-care/beauty/sun-care/sunscreen5.htm>
How Things Work. "How Black Light Works" Discovery 2011. <http://science.howstuffworks.com/innovation/everyday-innovations/black-light.htm>
Darvill. "X-rays" Darvill, 2009. <http://www.darvill.clara.net/emag/emagxray.htm>
Darvill. "Gamma Rays" Darvill, 2009. <http://www.darvill.clara.net/emag/emaggamma.htm>