Introduction: The Color Mixing Puzzle

About: I am a hobbyist with an interest in open-source software, 3D printing, science and electronics. Please visit my store or Patreon page to help support my work!

White light is made up of many colors of light. This Instructable shows how you can split up, redirect and recombine colored light using prism cubes in a mini "puzzle" that challenges you to think about white light in terms of its constituents parts.

Step 1: What's an X-Cube?

In digital projectors, prisms are assembled into a cube that combines independent red, blue and green images into a full-color image for projection. When used in this application, they are called cross dichroic prisms (X-cubes) or an RGB combiner/splitter. Such cubes can separate white light into red, green and blue components by directing each at right angles.

These cubes are quite expensive when new, you can salvage them from broken projectors or obtain small packages of chipped and/or damaged cubes on eBay.

Step 2: Making a Board and Pawns

Making a board and some pawns is extremely easy in TinkerCad. You can try designing your own from scratch, or you can start with my design for 20 mm cubes!

Then, simply print the results on a 3D printer using some white filament. If you don't have a 3D printer, you could make a board and some pawns easily using some paperboard.

Step 3: Thinking in Technicolor!

Now, set out the cubes and the pawns on the base. Move them around and shine a small flashlight from the sides of cubes. Challenge yourself to come up with interesting variations by rearranging the cubes. Here are a few ideas and questions to ponder:

  • What happens if you rotate the cubes 90 degrees?
  • What happens when you turn a cube upside down?
  • Can you arrange the cubes to make the "color mixing" and "left to right cross" examples I have shown?
  • Is there a way to change the direction of green light?
  • Can you make a pawn glow purple? How about cyan? Or yellow?
  • Can you come up with rules to make this into a mini-board game for two players?
Puzzle Challenge

First Prize in the
Puzzle Challenge