Teacher Guide

# Seeing Colors

## Experimenting with color contrast

What colors are beads in different colors of light?

This resource was originally published in PhysicsQuest 2016: Currents.

This is the teacher guide for this lesson. A student-focused guide to assist learners as they perform the activity is available.

View the student guide: Seeing Colors

What colors are beads in different colors of light?

• Red LED
• Green LED
• Blue LED
• Coin battery
• Dark room
• Four sheets of white paper
• Pencil
• Tape

Students will examine the phenomenon of the color difference of the blue and black dress. They will collect observable data and draw conclusions about the photo of the dress based on their data.

• Total time
45 - 60 minutes
• Education level
• Content Area
Light
• Educational topic
Light, color, contrast

Seeing in color is no easy feat. It involves the biology of the retina, the brain, and the light around us. Many animals can’t see in color at all, while others see many more colors than the human eye can see. When we see something in color, our eyes are detecting the color of the light reflected from the object. Our brain takes that information – along with the color of the surrounding light – and processes it to determine what color the object is. Most of the time, this works fine because we are surrounded by white light. But when the color of the light around an object changes, problems can arise.

When a red bead is in white light, we see it as red. Why? Because only red light is being reflected; all the other colors of light are being absorbed. The same is true with blue beads and green beads, etc. Your brain says, “Look at that! The light all around is white and only red is being reflected. That means this bead is red!”

White things appear white because all the colors of the light around them are reflected. We perceive objects as black when all the colors of light are absorbed. If you put that red bead into a room with only red light, it will reflect all the colors of the light around it. So your brain says, “Look at that! All the colors of the surrounding light are being reflected. The bead must be white!” You see the bead as white.

This explains the famous blue-and-black (or white-and-gold) dress: it was a case of a blue dress being viewed in shaded blue light. Blue light reflecting off a blue dress made our eyes see white. Similarly, a green bead in a blue LED light will look grayish because the blue LED is producing a bit of green light, and that bit of green light is being reflected.

The LEDs you will use in this kit look like they produce red, blue, and green light. However, that’s not entirely true. The red LED produces bits of orange and yellow light. The green LED produces a bit of yellow and blue light. The blue LED produces a bit of green and purple light. Because it is important to know what colors are being produced by the LEDs, the image shows pictures of the LEDs as seen through a diffraction grating. The diffraction grating breaks up the light into different colors so you can see what’s actually being produced.

Key terms

These are the key terms that students should know by the END of the two lessons. They do not need to be front loaded. In fact, studies show that presenting key terms to students before the lesson may not be as effective as having students observe and witness the phenomenon the key terms illustrate beforehand and learn the formalized words afterwards. For this reason, we recommend allowing students to grapple with the experiments without knowing these words and then exposing them to the formalized definitions afterwards in the context of what they learned.

However, if these words are helpful for students on an IEP, ELL students, or anyone else that may need more support, please use at your discretion.

• Circuit: A circuit is a closed loop through which charges move.
• Current: Flow of positive charges. When a complete circuit is created with a battery, current flows.
• Resistance: Resistance slows current down. The more resistance something has, the less current flows through it.
• Rheostat: A rheostat is a circuit element that can change its resistance. Things like volume control knobs and light dimmer switches are examples of rheostats.
Objective

Students will experiment to understand why colors can look different depending on the contrast or light.

Before the experiment

Why do you think this dress is so confusing to our eyes and brain?

• Turn & talk protocol
1. Pair students up.
2. Give them a minute to think quietly.
3. Give students 2 minutes to discuss their thinking.
4. Have students record their answers or share out to the whole group.
Setting up
• Take your pile of beads and sort them into colors on a sheet of paper labeled “white light.” Draw a circle around each color category and label it with the color you see.

• Connect the green LED to the battery to light the LED.

• Turn off the classroom lights so that the only visible light is from the green LED.

• Again, sort the LEDs into colors on a white sheet of paper labeled “green light,” using only the green light from the LED. The number of groups may be different from what you found on your “white light” paper.

• Label each category with the color you see – not the color you think they are in white light, but the color you see in green light. These new colors may include things like gray and black.

• Turn on the lights again. Write down what color beads appeared to be what colors in green light. So if you had a circle labeled “gray,” write down what color beads were in that circle when you turned on the lights.

• Repeat steps 2 - 6 using the blue and red LEDs.

During the experiment
• Make sure students are put into intentional groups. See teacher tips below.

• Students will complete the experiment using the Student Guide where we have outlined the experiment for students and along the way, they record results and answer questions.

• In the Student Guide, they will answer questions that help them understand color.

• Continue to listen in on each group’s discussion; answer as few questions as possible. Even if a group is off a little, they will have a chance to work out these stuck points later.

Teacher tip
1. Suggested STEP UP Everyday Actions to incorporate into activity:
1. When pairing students, try to have male/female partners and invite female students to share their ideas first.
2. As you put students into groups, consider having female or minority students take the leadership role.
3. Take note of female participation. If they seem to be taking direction and following along, elevate their voice by asking them a question about their experiment.
2. Consider using white boards so students have time to work through their ideas and brainstorms before saying them out loud.
3. As students experiment, roam around the room to listen in on discussion and notice experiment techniques. If needed, stop the class and call over to a certain group that has hit on an important concept.

Consider using the RIP protocol (Research, Instruct, Plan) for lab group visits and conferring.

Consider culturally responsive tools and strategies and/or open ended reflection questions to help push student thinking, evidence tracking, and connections to their lives.

Conclusion
• Use the claim-pass protocol to have students share and refine their thinking.

1. One person in each group writes a claim (can be provided by the teacher or not) at the top of a paper with the following question: In what color light do you think the blue black/white gold dress was photographed? Why?
2. Pencil in response to a recent observation of a phenomenon.
3. The student who wrote passes the paper and the pencil to the left.
4. The person with the paper writes one piece of evidence that supports the claim.
5. Pass the pen and pencil to the left.
• After students have had a chance to discuss key ideas from the lesson and complete their student guides, you can now clarify and give concise definitions to the forces they experimented with.

• Real world connections:
• In order to see color, humans have three cones in their eyes. For more information about cones and vision, see How Cones and Rods Function in the Eye and Seeing Color. Based on this, and what you learned about seeing colors in this activity, what do you think happens when people are color blind? What about animals that have more cones in their eyes – what do they see?
• Suggestions for drawing, illustrating, presenting content in creative ways:
• Have students create a drawing similar to the blue-black dress in groups. Then put the images in different lights, and have students try and guess what colors the drawing is actually in.
• Engineering and design challenges connected to the content:
• Continue exploring this content using these PhysicsQuest 2023: Making Waves activities about multiplexing: Slinkys, ChromaDepth Glasses, Energy of Light, Multiplexing Messages.
• MS-PS4-3-applications
CCC: Influence of Science, Engineering, and Technology on Society and the Natural World. Technologies extend the measurement, exploration, modeling, and computational capacity of scientific investigations. (MS-PS4-3)
• MS-PS4-3-nature-of-science
CCC: Science is a Human Endeavor. Advances in technology influence the progress of science and science has influenced advances in technology. (MS-PS4-3)
• MS-PS4-1-empirical-evidence
SEPs: Scientific Knowledge is Based on Empirical Evidence. Science knowledge is based upon logical and conceptual connections between evidence and explanations. (MS-PS4-1)

### Credits

Created by Rebecca Thompson, PhD, David Ellis, Amanda J Ellis

Activity layout by Donna Giachetti

Images by James Roche

Updated in 2023 by Sierra Crandell, MEd, partially funded by Eucalyptus Foundation

Extension by Jenna Tempkin with Society of Physics Students (SPS)