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Physics of Media Arts: Conceptual Physics for Students of the Media Arts

Aaron Wong

Lab Activity 13.5.1 Colored Lights and Shadows

Introduction.

This lab is an exploration of colored lights and shadows. We will be playing around with different types of setups to help us understand what colors are being created and why.

Equipment List.

  • Red, green, and blue flashlights
  • Plain white paper (whiter is better) for a "wall"
  • Index card, paper, or thin cardboard to cast shadows
  • A couple pencils or other similarly-shaped objects
  • Scissors
  • [Optional] Camera (photo or video) for capturing visual data.

Procedure.

For this lab, we are going to start by using a set of red, blue, and green lights to get a white light. Then we will create shadows and various colors and try to understand the ways that lights are combining to create those colors.
  1. Create a "wall" using the white paper. You need a place to shine your lights and create shadows. This could be a piece of paper leaning against a book or a binder, or even just folded in half. It only needs to stand a few inches tall.
  2. Using the paper for the shadows, create two thin strips that are a few inches long and an inch wide. You will want a clean side edge where the two strips can be brought together like a curtain. The exact dimensions are not important. In one of the strips, create a slit that is about a quarter inch in width. Use the diagram below as a model.
  3. Line up the three flashlights side-by-side pointing towards the wall. Make a note of which light is in which location.
  4. Darken the room as much as possible and turn on the lights. (Note: If the flashlights have multiple settings, pick the brightest non-blinking option.) Position them so that they combine into a white light in the middle. There may be other colors on the edges, but we’re not going to worry about that. From this point forward, you may want to take pictures or video of the lab for future reference.
  5. Hold the strip of paper with the slit in it between the lights and the wall. You should see three lines of light of different colors if you move it close enough to the wall. Identify the colors and think about why the colors appear in the order that they do.
  6. Hold the pencil between the lights and the wall. You should see three shadows of different colors. Identify the colors and think about why the colors are what they are. Then take the paper with the slit in it and place it between the pencil and the wall to create the three lines from before. Move the pencil so that its shadows cross the slit (one at a time) and make a note of your observations. Think about what is causing these outcomes.
  7. Put two strips of paper end-to-end like a closed curtain and position them between the lights and the wall. Slowly separate the strips to reveal a thin slit. You should see three light lines similar to the paper with the slit. Continue pulling the papers apart and watch how the lines spread out. When the lines touch each other, make a note of the colors that are created. As they continue to get further apart, you will see a number of different color patterns. Make note of each one. You will eventually have just two sets of shadows, one from each piece of paper. Think about what is causing these outcomes.

Discussion.

After you’ve completed the tasks, answer the following discussion questions. Some simple diagrams have been included to help you to explain your observations.
  1. In the first phase, you created three lines of light. Explain why the lights appear in the order that they do.
  2. In the first part of the second phase, you created a set of three colored shadows. Explain why you see the colors that you saw in the order that you saw them.
  3. In the second part of the second phase, you created an interaction of three colored shadows with the slit. Explain the relationship between the color of the shadow and which line disappeared.
  4. In the third phase, you created a sequence of several different color patterns. Draw them and explain how each color pattern was created.

Conclusion.

As you went through this lab, you should have started to develop a stronger sense of how colors of light mix together. There is also a connection to be made between the additive and subtractive interpretation of colors. In the first phase, you were displaying the additive nature of light by allowing certain colors to shine through to the black shadow. In the second phase, you were displaying the subtractive nature of light by blocking certain colors from hitting the white wall. And in the third phase, you exhibited how the two perspectives are part of the same underlying reality of colors.

Lab Write-Up Guidance.

Use the following outline to help you write up your lab report completely and correctly.
  • Title and Header.
    What is the title of the lab and who was in the lab group?
  • Introduction.
    In your own words, what was the purpose of the lab activity? You should be able to condense the core purpose to just a few sentences.
  • Equipment List.
    List the equipment that you actually used. Try to be clear in your description. For example, did you use a pen, pencil, or something else? How large were the papers you actually used? And what material were they (office paper, index cards, etc.)?
  • Procedure.
    Write down the steps that you executed. This should be similar to the given procedure, but it’s possible you may have done something out of order, or perhaps you skipped something or did some additional experiments. The important thing is to just be sure you captured your actual activity.
  • Results and Data.
    Your information should be organized by the three phases of the lab activity. If you took photos or videos, this would be a good place to include those images. If you didn’t, then you’ll need to describe the results in words. Make sure to present the information in a way that is easy to understand. For example, avoid using a wall of text to describe something that might better be presented as a picture.
  • Discussion.
    Answer the questions in the discussion. Be sure to include diagrams that are helpful for explaining what’s happening.
  • Conclusion.
    Write a paragraph or two that summarizes the lab and what you learned from it. You should reference additive and subtractive colors in some form. Be sure to include information about any particular moments of insight (or intrigue) that you had.
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