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Mix red, green, and blue light using a pinhole viewer and conduct simple scientific investigations into human color perception.
Build your pinhole viewer:
Put together your light source:
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!
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:
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.
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Attribution: Exploratorium Teacher Institute