visible spectrum on hand

As you look at the horizon after a rainstorm, you see it in looming in the distance. It’s a rainbow. Of course, there’s no pot of gold at its end, but there is a wealth of knowledge that the rainbow can teach us about wave diffraction.

How about a more man-made phenomenon? As you spin a CD back and forth between your fingers, the back of the disc flashes a brilliant array of colors. Why does the CD react like this? It’s simple: the principles of interference and diffraction are at work, causing you to see these gleams of color.

Have you ever wondered how these kaleidoscopes of colors are produced? They are all around us. Not only do you see them in rainbows and CD’s but you can also observe them in bubbles, glass, and holographic stickers (just to name a few). So what exactly is this phenomenon?

Understanding the Science of Light

Before we consider interference and diffraction, we have to take a moment to consider what light is and how it travels. Waves are part of the electromagnetic spectrum, and they carry information from one place to another. Waves can carry different types of information, like light and sound. Some of these waves we are able to discern, but others are beyond our abilities to process.

Waves can be used many different ways. Radio stations transmit their signal via sound waves. Microwaves cook our food through the power of (unsurprisingly) microwaves. X-rays are harnessed by special machines that allow us to view inside our bodies. Waves are everywhere!

Right in the middle of the electromagnetic spectrum are light waves. These waves travel from a source and help us discern both light and color. So where does interference and diffraction come into this picture?

What Happens When Light Waves Bend

When light waves travel to our eyes on a straight and unimpeded path, we discern colors in a fairly straightforward fashion. However, it’s when light waves take a detour on the way to our eye that they react in unique and colorful ways. When waves are diverted by particles in the air or other light waves, their path and even their wavelength can change. This effect is called interference or diffraction.

rainbow over farmland

So, is there a difference between interference and diffraction? The scientific answer is this: not really. They are designations that don’t have a firm difference between the two. However, when most scientists talk about a small amount of sources diverting light waves, it’s usually called wave interference. When there are many different sources, it’s usually called wave diffraction. In the end, though, the two names describe the same concept.

The Effect of Interference and Diffraction

Let’s imagine for a moment that we’re looking at the evening sky after a pouring rain. As the sky starts to clear, a beautiful rainbow appears in the distance. How does interference and diffraction play into this beautiful natural phenomenon?

As you stand on your front lawn and see the clouds move away, the rain slows down and eventually comes to a stop. However, as you look to the horizon, you can likely see that, although it’s no longer raining where you are standing, there is still precipitation coming from the clouds. If these water droplets are in between your position and the sun, they represent an opportunity to see wave diffraction at work.

As light waves travel through the rain falling in the sky toward your eye, they can’t travel in a straight path. Imagine the light waves travelling through the rain like a pinball, bouncing around back and forth before they finally make their way back to your eye. What is the result of this? You end up seeing all seven colors of the visible spectrum in the natural wonder we call a rainbow. All of this is brought to you thanks to the work of interference and diffraction.

Everyday Observances of Interference and Diffraction

Of course, we don’t have the opportunity to see rainbows of a regular basis. Conditions in the atmosphere have to be perfect for us to witness one. But that doesn’t mean interference and diffraction are rare. In fact, we witness it so often that we probably don’t even realize it.

If you look at a piece of glass on your home, car, or even your smartphone, you can often see the array of colors that flash as your point of view changes. This is wave diffraction at work. Sometimes merchandise sold at stores have holographic stickers attached to them. These stickers are hard to duplicate, so they are a way to show that the item you are buying is authentic. As you turn the tag back and forth, you’ll see the variety of colors that pop and flash.

Even something as simple and beautiful as a suncatcher shows the practical use of interference and diffraction. As light waves travel through the opaque colored panels of the suncatcher, the light waves change and allow us to see a variety of colors. Stained glass windows work on the same principle as well. As light waves from the exterior of the building travel through the pieces of colored glass, the result on the interior of the building is a breathtaking display of colors and light.

stained glass cathedral

As you go about your day, can you find other examples in nature of interference and diffraction? When you look at your home, do you see ways that this phenomenon produces an array of colors? Once you begin to look, you’ll see it all around you.

However, if you always want to have access to the rainbow spectrum no matter where you are, or if you would simply like to give someone else the colors of the rainbow, then consider picking up a pair of our diffraction glasses, rave glasses, or our diffraction grating slides to bring the color spectrum to life!