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Poking Fun at Color Mixing

Science Snack
Poking Fun at Color Mixing
Enlarge your perspective on color.
Poking Fun at Color Mixing
Enlarge your perspective on color.

Mix red, green, and blue light using a pinhole viewer and conduct simple scientific investigations into human color perception.

Tools and Materials
  • Cardboard tube measuring approximately 2 to 3 inches (5 to 8 centimeters) in diameter and 4 to 7 inches (10 to 20 cm) in length (such as from a roll of paper towels or gift wrap; poster tubes and PVC tubes will also work)
  • Aluminum foil
  • Wax paper (or a white translucent plastic bag)
  • Two rubber bands
  • Pushpin
  • Red, green, and blue screw-in light bulbs, one of each color (can be CFL, LED, or incandescent)
  • Three screw-in light sockets
  • Power strip with at least three parallel outlets
  • Power source (and extension cord if needed)
  • Darkened room
  • Partner
  • Optional: black construction paper, two additional rubber bands

Build your pinhole viewer:

  1. Cut the wax paper to a size slightly larger than the diameter of the tube. Do the same with the aluminum foil.
  2. Cover one end of the tube with the cut piece of aluminum foil, folding the ends over tightly and securing the foil in place with a rubber band.
  3. Cover the other end of the tube with the cut piece of wax paper, also folding the ends over tightly and securing in place with a rubber band. Make sure the surface of the wax paper is as smooth and wrinkle free as possible; this will be your viewing screen.
  4. Optional: for better viewing, you may want to add a shade to your screen (wax paper). Roll the black construction paper around the wax paper end of the tube, leaving the foil end exposed by a few inches (10 cm). Secure the construction paper in place with rubber bands.

Put together your light source:

  1. Screw the red, green and blue bulbs into the light sockets.
  2. Plug all three sockets into the power strip and plug the power strip into the wall, but don’t turn the lights on yet. Place the power strip on a table or other surface.
To Do and Notice

With a pushpin, make a small hole in the center of the foil on your pinhole viewer. Next, use your finger to enlarge the hole. The hole should be a few centimeters in diameter. It can be ragged or circular in shape.

Make the room as dark as possible, then have your partner turn on the red and green lights that are mounted on the power strip while you position yourself about six feet (2 meters) away.

Orient the viewer so the foil side is facing the light source and the wax-paper side is facing you. Hold the viewer up to the light, about 8–10 inches (20 centimeters) from your face, and look at the light being projected onto the wax paper.

Try to get the light from the green and red bulbs to overlap. What do you notice? What techniques or modifications produce overlapping colors? Make sure you can get the colors to overlap before continuing.

Next, ask your partner to switch off the green light and turn on the blue light (leaving the red light on). What do you notice?

Ask your partner turn off the red light and turn on the green light and the blue light. What do you notice?

What do you see where the images of the colored bulbs overlap? Use this document to record your findings.

What you will see when all three lights (red, green, and blue) are turned on and overlapping? Try it and record your observations!

What's Going On?

Did the combinations surprise you? We have millions of light receptors in our eyes, but we have only three types for seeing color—each sensitive to certain wavelengths of light corresponding to the red, green, or blue part of the spectrum—that’s it! These receptors, located in the back of the eye, are called cones.

All the colors we see in the world around us are caused by different wavelengths of light stimulating one, two, or all three types of cones. When our cones are stimulated, our brain receives a signal and processes the information in ways that allow us to perceive color. Depending on how much stimulation each of our RGB cones receives, we perceive a different color:

  • We don’t have yellow cones in our eyes. Although yellow light exists (or wavelengths that correspond to yellow), our eye-brain system causes us to perceive yellow when our red-sensitive and green-sensitive cones are stimulated in roughly equal proportion.
  • We don’t have cyan (or aqua blue/turquoise) cones (although there is a range of light wavelengths that correspond to cyan)….again, this color is made up in our heads by light activating both the blue-sensitive and green-sensitive cones.
  • We don’t have magenta (or purple/pink) cones, nor is there even a wavelength of visible light that corresponds to this color. The eye-brain system totally makes this color up when our red-sensitive and blue-sensitive cones are activated together!
  • Overlap and activate all three cones and what do you see? White light! That’s the way our eye-brain system works.
Going Further

Many significant technologies rely on our ability to perceive all the colors of the visible spectrum using only RGB lighting. Investigate and see which ones you can discover.

Try dimming down one or more of your RGB lights. If you have dimmer sockets, try changing the intensities of the lights or block some of the light by using your hands. Can you make other colors this way?

Did you notice that as the pinhole got bigger, the image got brighter, but also blurrier? Is there a better way to get a bright and sharp image? Try some other designs with your viewer and bulb apparatus.