Making Spectra (Rainbows) with Prisms. A primer.
Prisms! We love ourselves some prisms!
Whether they are glass, acrylic, water filled, or even hollow prisms are a great way to bend light and have fun doing it.
Of course one of the more fun aspects of prisms is using them to make rainbows (or spectrum to be scientific). Some of these prisms it is easy – just put the prism in a sunny window and it will project random rainbows around the room. But for a more scientific appearance of spectra you have to use a proper prism (typically equilateral). Trouble is, it is not as easy to do as making random rainbows with water prisms. Many folks have bought prisms as came to us saying “they didn’t work”. Which is kind of like saying a ball is broken because gravity didn’t somehow pull it to the ground. It just doesn’t work that way. That being said making spectra with a prism is not as easy as dropping a ball. Here are some critical tips for making a proper spectrum with your prism.
- Darken the room
The biggest issue with making spectra is that they can get washed out by other light, or be so feeble to be unseeable. So darken the room as best as your can. Turn out the lights, draw the curtains, whatever makes the room darker. The contrast will make the spectra look better.
2. Make a Slit lamp.
OK, so you might have noticed something about that Light Crystal packaging up above. Let’s have another look:
You may notice the pretty spray of colors on the right, but look at the leftof the crystal. You might notice there is a column of light entering the prism. Note that it is almost a beam, not an entire wall of light from a bulb or sunlight. This is important:
If you try to make spectra with a bulb, flashlight or sunlight, odds are you won’t get very good results. The wash of light entering the crystal will result in a wash of light coming out of the crystal. It won’t be as good as making your own slit lamp.
How do you make a slit lamp? Well, get yourself a powerful flashlight (not too powerful…some high-power models out there can overwhelm the black construction paper you will be using) and some black construction paper. Then using the diameter of the front of the flashlight as a guide, cut out this shape from the construction paper:
You are making a circle with a slit in it to cover the front of your flashlight, so cut this circle out a little larger than the front of the flashlight. You can make multiple versions with slightly larger or smaller slits so you can see what works best (flashlight deisgns and room darkness conditions may produce differing results).
3. Shine on, you crazy spectrum maker
With your darkened room, prism in position, and slit-lamp adjusted flashlight, aim the beam of light at the side of the prism. Typically, this means hitting the side with the beam slightly below one of the edges. The angle you aim at the side will affect where the spectra appears. Aim from on high and your spectrum will appear on the floor, aim from below and you could have it on the ceiling. Which reminds us:
4. Have a good target wall/ceiling/paper
If you have a wall painted red, and project a spectrum on to it, guess what? A good portion of the colors won’t show up very well. So always aim for a white wall or ceiling, or at least put down some white paper to get the best spectra.
Enjoy the colors!