MicroWorlds Contents | Advanced Light Source | Berkeley Lab
   
 

Selective Absorption Activity

   
 

Why do you wear sunglasses on a bright day? The gift of sunglasses is that they absorb some sunlight so that it doesn't reach your eyes. If you look at a new pair of sunglasses in the store, it may have a label that reads, UV A and UV B protection.

This means that, in addition to absorbing some visible light, the glasses selectively absorb some UV rays that are harmful to your retina. It sounds so simple, but it is easy to forget that you only see the light that gets to your eyes.

The following activity allows you to explore how the appearance of things change when different colors of light are selectively absorbed.

Materials: Look around for items that can act as transparent colored filters. Collect at least three different colors such as red, blue, and yellow. Some filters that work best are thin sheets of colored cellophane or transparent plastic. However, you can also use tinted sunglasses, colored glass or plastic bottles, jars filled with water and food coloring, or any other colored, transparent object.

Action: You will use these filters to view the next picture. Look at the picture without any filters and pay particular attention to the colors of each part. Look again at the picture while holding one of the colored filters up in front of your eyes.

  • NOTE: It may be helpful to turn off or dim the lights in the rest of the room. Also, if you are color blind, you may not see the same kinds of changes in the picture as someone who isn't color blind.
    • What do you notice?
    • How do the colors change when looking through different filters?
    • Are there any colors that appear bright or others that almost disappear?
    Repeat looking through the colored filters until you have tried them all. While you are doing this, it may be helpful to make a table of your findings so that you can compare the effects from each different colored filter.

    Ask yourself some questions and see if you can discover a pattern between the color of the filter and the colors that you see. For example, when you look through a bluish colored filter, what is the dominant color you see? What parts of the picture show a dramatic color change? How do the colors change--from what color to what color?

    Explanation: To help you understand what is happening, remember that you only see the light that gets to your eyes. When the colored light from the computer screen passes through the colored filter, some of the light is absorbed and some is allowed to pass through the filter and continue to your eyes. The filter is named for the color of light that it allows to pass through. For example, red cellophane would be called a red filter. The cellophane would allow primarily the red tones of light to pass through and reach your eyes.

       
     

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