In this post, we are going to spend a bit more time with color--light and pigments. By now when you hear the words
reflect and
absorb, each should have new meaning to you. Now what happens when we mix colors from either type?
Have you ever wondered why a stage looks white when all the stage lights are not white?
Perhaps, you were able to use the color mixing guide for light in the image above this one to answer my question.
Transmission, Reflection, and Absorption
We already know that the color of an opaque object is the color that it reflects. The color of a transparent or translucent object is the color that it transmits. What exactly does this mean? This means that the color of an object depends on the light that shines on the object and the light that that bounces off or is transmitted through the object.
Look at the two windows below. The first window (which is transparent) is only transmitting white light because it allows all colors of light to pass through. However, the stained glass handles light a bit differently. The color of the glass determines what colors will be transmitted through. In other words, green blades of grass in the stained glass only transmit green light and absorbs all others.
So what colors of light are transmitted through the trophy in the stained window glass?
This takes us into the topic of color filters. I am sure you have seen color filters one time or another, but what happens when a color filter is placed in front of an object? A couple of things actually occur. Can you tell from the pictures below what happens? (These pictures should look familiar as they were taken from the textbook.)
The images show the red filter only allows red light waves to transmit or pass through while it absorbs all others. As a result, the red on the apple is reflected and still looks quite red behind the filter. However, the apple leaves don't appear green behind the filter. Instead they appear black. You can see what happens when the color filter is changed to green and then blue.
In these cases what colors would be absorbed, transmitted, and reflected?
I guess before I wrap this subject up we should just address two more things. Is there really such a thing as black light? What happens to objects when there is no light?
For question one, check out this
informative website. As far as the second question is concerned, let's revisit the first image on this post. When you mix any or all of the colors of light, none of the combinations make black light. So why do objects appear black, especially at night? Well the answer is simple. Objects appear black because there is an absence of light. What? That's right! This means that there are no available colors of light reflecting off of the object, therefore, the object will appear to look black. Remember to see color, the cones and rods in our eyes need to absorb and focus the light waves to determine the colors we see. Without the light filtering into our eyes, our eyes will not be able to pick up the colors on the object.
Over the last final days of this semester, we will be engaging in light lab activities. You will need to take all that you have learned and connect it to the activities. Before I wrap up, I spent some time sharing these images created with an iPhone, a prism, and a spectroscope. How about you share what you learned about these items and what they have to do with light with your parents. You can also make your own spectroscope by following the directions found
here.
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| Created with a spectroscope (The light is focused and then passes through a prism inside the spectroscope.) |
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| Created with an iPhone and an equilateral prism (The objects are located to the sides of the front-facing camera.) |
