Light and Color Lab

Add all the colors of light together and you get white? But add all the colors of paint/ink together and you get black? Really? These concepts are often a bit difficult for students to grasp. I introduce this lab asking if students have ever printed off an images from their computer but the colors were all wrong. That's because monitors use additive colors and printers use subtractive. 

This lab consolidates labs on subtractive and additive color. I knew there was a difference, but when studying color, I didn't find a lab that helped students to compare the two. So I wrote my own. (Free printable of student handout along with teacher answer key at the end of this post!) This lab is not a high level of inquiry--instead it is collection of several demos and activities to help students solidify what is true about color and light. I used this lab with middle/high school students, but used parts of it with my 5 year old! If you have a class of 25 or more, you might choose to set this this lab up in stations where they rotate to various activities.  

Comparing additive and subtractive colors

You don't need any materials for the section on comparing additive and subtractive colors. This is a chart that students fill in as they learn about the properties of these two color systems. Here is a look at the answer key. 

Refraction of Light activity

Materials needed

• three beakers or mason jars
• 3 straws

Light moving through a Prism

Materials needed

• Flashlight
• prism
• white paper

Here's another simple one. Give students a flashlight, white piece of paper, and a prism, and tell them to play, and see what cool artistic images they can come up with. If they don't already know, they'll see a rainbow, and then work the light around different places on the prism to get the best view! 

Effects of colored light on what we see

Materials needed:

• Swatches of red, green, white, and black paper or felt 
• Colored lights (white, black, red blue, and green)  

This is the part of the lab I like best. I taped up our color color swatches on the wall in a closet, and the used a lamp with different colored bulbs to do this lab. You could also use white light and colored cellophane, but I found it was a lot cheaper and easier to buy the party bulbs.   

My students were amazed at what a difference the colored bulbs made in some instances. Its good to have black as a comparison, because with the green light, the green swatch looks black. For many of the the others, the colors are just tinted by the bulb, not completely changed. Consider too having students predict what sort of changes they anticipate with the colored bulbs. Students learn about reflection and absorption of light, and how those make the colors we see.

My favorite take-away for students in this section is that a color isn't "technically" the color you think it is! Its actually every color BUT that color. 

For example, when you look at green paper (with white light) all of the colors of light approach the green paper. The paper absorbs all of the colors EXCEPT green. Green is the one color "rejected" (I use this word as a way to make the process seem all the more dramatic) and therefore is the color reflected into our eyes. Here our brain is perceiving this color and we identify it as green.

Here are the results we got doing this portion of the lab.    

In down time, before moving on to subtractive colors, I also had these Color Paddles out on the table for students to play with. They held these up to the window and then overlap them to see how colors combine. One the right is a color wheel I use when scrapbooking, and I had that available for the next section in mixing colors.  

Mixing Color Activity

Materials Needed

• art colors (chalk, water colors, acrylics or what ever you have)

Like the other sections of this lab, the application of the concepts are simple, even elementary, however, I did this lab with high school boys. The idea is to provide them with experiences of lights of color to compare it to mixing of artist colors. I had an array of art supplies available for them (my science room doubles as an art room, so that was easy!) And I let them play. The student handout has a place for them to mix two colors, and then describe what they see. A space for 3 colors, and then 4. Its good practice for both scientists and artists to be able to accurately describe what they have created.   

The challenge is the last two tables where I ask them to "mix colors to make the color black without using black" and then to "mix colors to make the color white, without using white." Most students can get a color close the black. But mixing white, stumps them, and it should. They can't do it, its a trick question. (he-he) 

Perceiving Color

The last section of the lab is called Perceiving Color, and ties back to my prelab question, "Is seeing always believing?" Depending on the level at which your students like to talk philosophy, neurobiology, and perception, this can be a fun discussion. Is our perception reality, or only how we perceive it? If science evidence supports something that doesn't seem to be the way we see it, which is right? You see what I mean. Let students help guide this discussion, or leave it out entirely! Up to you!

Light and colors are introduced at very young ages. My 5 year old enjoyed all of these demonstrations and activities. But the science behind it is really neat. Do you like discussing the philosophical applications of science....like the comment I made about green not actually being green? I find students respond to that sort of thing. And that's the thing they'll share with their friends...therefore that's the cool part of science. I figure if I got them talking about it when they're not in class, I won! :)

Download the free student printable with Teacher Answer Key!