Have your kids ever asked you what makes a rainbow?

Or why we only see rainbows when it is raining?

The answers all come down to how light reflects and refracts through matter.

And, in the case of rainbows, through the water. As light is refracted through the tiny droplets of water, it separates into colors. We need the white light from the sun, and the droplets of water, to make all of this happen.

Imagine light as a super great track star.

Better yet, imagine it as a stellar track team. The team has billions of runners, but to keep it simple, let’s just look at a few runner: red, orange, yellow, green, blue, and purple.

In the air, these guys are all running at the same speed, even though purple is a big heavyweight runner and red is a wispy waif.

Now, let’s pretend our crew is running the pinnacle of steeplechases and enters an area they call glass alley.

Glass alley is full of big balls of glass that runners have to weave in and out of. The balls are in a nice structure, like dots on the edges of a square, for example. 

Our thin waify red and easily navigate through these dots, although red will slow down some, and have to change their direction to keep on running. Purple, on the other hand, is going to have a whole lot more trouble getting through all of these glass balls. Purple will have to go a lot slower and turn a lot more to make it around all of the glass balls.

Now, this isn’t a perfect analogy, but what happens is the red travels faster in glass alley, and barely needs to bend to get around the obstacles. Purple travels much more slowly and has to bend a lot. At the end of glass alley, two things will happen: red will emerge first, and will also emerge going along the straightest path. Purple will emerge last and will also emerge at a bent angle compared to what it went in at. 

Thus red emerges on top, purple on bottom, and I will let you guess where the other colors fall into place. 

In a rainbow, we have mist alley instead of glass alley, but again, red can move through the water the fastest, while purple is the slowest. Red moves through without having to bend too much, while purple has to bend around a lot. Thus on the other side of the water droplet you don’t have white light, but instead red on top, then orange, yellow, green, blue, and finally purple on bottom. 

Want to see the process of bending light in your own home? You can make edible optics! You won’t need too much, and we outlined it for you below!

Get started making your own edible optics

We have an in-depth guide to making the gelatin you will need to make your edible optics, but for the most part, you need 1oz Jello, 0.25oz Knox gelatin, and 1/3 cup of water.

Making lenses out of Jello.

Now that you have thick Jello made you can make your own lenses. This is where the round cookie cutters come in. Optics we use in our everyday lives, like glasses, have nice smooth curves to them. While you can cut your Jello at various jagged angles and watch how the laser beam enters and exits the Jello, you can get a better idea of how lenses work if you have smooth curves.

There are two main types of lenses, convex and concave. Basically, lenses that bubble out, or lenses that cave in. 

Using a square of Jello and your round cutters see what kinds of shapes you can make. Below is an image of a few types of lenses. Using your lasers, and noting how it affects the path of the beam, can you figure out what converging lenses do? What about diverging lenses?

Challenge yourself to make each type of lens above using your round cutters – can you see where the circular shapes are? You’ll need to add or subtract the circles to get each shape, so this is a fun lesson in geometry as well!

What lenses could you make? What happens to the laser beam if you have a curved piece versus a straight piece of Jello? What happens when you point the laser down a long skinny piece of Jello?