Mixing Colors with Light

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Students experiment with different colors of lights to understand how they combine to create new colors.

Big Idea

Different wavelengths and frequencies of light correspond to different colors of light.

Context and Supplies

Building off the previous series of lessons on waves, students apply their understanding of wavelength and frequency to colored lights. They do this with a series of stations, some with actual colored lights and others with a computer simulation. Students also get to color the primary colors (blue, red and green) as well as the secondary colors (yellow, magenta and cyan). This lesson requires three colored light bulbs (red, green and blue) which can be purchased at Lowes for less than $20. For one station I have an older TV screen (with glass front) that students can put a lens against so that they can see the colored pixels illuminated to create different color combinations. Finally, this lesson requires markers or crayons and computers with internet access.

NGSS Science Practice 2: Developing and using models, Science Practice 6: Constructing explanations (for science) and designing solutions (for engineering) and Science Practice 7: Engaging in argument from evidence, as students must make observations on what they see and construct an explanation. The performance standard HS-PS4-1: Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media is also applied. Also applied is HS-PS4-5: Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy as the colored lights transmit specific wavelengths of electromagnetic radiation.

Colored Light Demonstration

10 minutes

I tell students that light is a wave and has all the properties of waves, including wavelength, frequency, and period. I pose a question to the class: "How do we perceive the differences in the wavelength or frequency of light?" Many students raise their hand and I call on one who likely gives the answer "color" or "different colors correspond to different frequencies of light". This is a well know fact by most high school juniors and seniors. I congratulate them on their knowledge and ask another question. "The color spectrum of light follows the pattern made by a rainbow. Where is pink? Where is white? How do we make colors that are not part of that rainbow pattern?"

I have three colored lights set up at the front of the room; red, green and blue. With the rest of the lights turned off, I demonstrate how different the combinations of lights mix to give different color combinations. The demonstration is similar to this video posted on Youtube by bockphysics. I shine the colored lights on the white board and use a dry erase to labels the colors. Red and green mix to give yellow, Green and blue mix to give cyan (I tell the students that cyan sounds like skyan which looks like the color of they sky) and blue and red mix to give magenta. 

Next I give the students instructions on how they are to explore the concept of color and light for the rest of the lesson.

Colored Light Stations

30 minutes

All students get the Color Basics activity sheet which they must complete in the next 30 minutes. Students work in groups of 2-3 so that they can discuss their observations and share the available supplies. The activity sheet has students going to three different stations. I inform the students that they have 15 minutes to complete station 1 and 15 minutes to complete both stations 2 and 3. Half the class does station 1 while the other half move between stations 2 and 3. After 15 minutes, I move the students at station 1 to stations 2 and 3, while the other half moves to station 1. 

Students at Station 1 use a computer to navigate to a PhET simulation entitled "Color Vision" as detailed on the front of the worksheet. Students use three different colored lights in different combinations in order to determine which colors are perceived. They answer questions such as "What are the three primary colors for addition?" and "What combination produces white light?" Again, students have 15 minutes to complete this station.

Station 2 has a computer monitor that displays a Power Point slide with several different colors including purple, red, blue, yellow and white. Students use a magnifying glass to see which pixels are illuminated for each of the displayed colors They put their answers on the Color Basics worksheet.

Station 3 has colored lights set up in the front of the room for the color demonstration and is the final part of the activity sheet. Students color in overlapping circles like the lights they see on the screen. They also label the different colors. Students have 15 minutes to complete stations 2 and 3.

Debrief on Color Combinations

10 minutes

Once the time is up, we review the answers on the activity sheets. The big idea is for them to understand that many colors that we see on our computer screens, TVs and smart phone screens come from only three colored pixels: red, green and blue. I show the series of pictures on the Camera Close-Up which shows a picture of a camera screen under different magnifications. When zoomed in, you can see that the image is composed of red, green and blue pixels.

Then I show the students the TED-Ed video, What Is Color?, which provides a good summary of the information they have learned and how it connects to waves in general. 

For homework, students watch a TED-Ed video entitled How We See Color. This video builds off of the information from today's lesson and explains how our eyes detect different colors and color combinations. On a blank piece of paper, students are to answer the 8 questions on the "Think" section of the TED-Ed video site.