Science · 8th Grade · Waves and Information Transfer · Weeks 10-18

Absorption and Transmission of Light

Students will explore how materials absorb and transmit light, leading to the perception of color.

• Common Core State Standards
• MS-PS4-2

About This Topic

The color we perceive is determined by which wavelengths of visible light an object reflects, absorbs, or transmits. An apple appears red because its surface absorbs most visible wavelengths and reflects those in the red range back to our eyes. A green leaf reflects green wavelengths. A transparent blue glass transmits blue wavelengths and absorbs others. These interactions follow consistent rules that 8th graders can investigate directly.

MS-PS4-2 connects this lesson to the broader framework of how waves interact with matter. Students explore why opaque objects appear colored (they reflect specific wavelengths), why transparent objects are colored (they transmit specific wavelengths), and why white and black objects behave differently from colored ones. They also investigate what happens when colored lights are mixed -- additive color mixing -- which is counterintuitive: mixing red, green, and blue light produces white, not a muddy color.

Active learning is especially productive here because the phenomena are visually striking and directly testable with simple materials. Using colored filters, flashlights, and paint mixtures lets students discover the difference between additive and subtractive color mixing through experiment. Predicting what color a red object will appear under blue light and then testing that prediction -- and resolving the cognitive dissonance when the result is black -- builds durable conceptual understanding that textbook descriptions cannot match.

Key Questions

1. Explain how materials absorb and transmit specific wavelengths of light.
2. Analyze how the interaction of light with matter determines the color we perceive.
3. Predict the color of an object under different colored lights.

Learning Objectives

• Explain how the absorption and transmission properties of materials determine the wavelengths of light that reach an observer's eye.
• Analyze how the selective absorption and transmission of light by an object result in its perceived color.
• Predict the resulting color of an object when illuminated by different colored light sources, based on its absorption and transmission characteristics.
• Compare and contrast the phenomena of additive color mixing with subtractive color mixing.

Before You Start

Introduction to the Electromagnetic Spectrum

Why: Students need a basic understanding of different types of electromagnetic waves and that visible light is one part of this spectrum.

Properties of Waves

Why: Students should have a foundational understanding of wave characteristics like wavelength and frequency to comprehend how different colors of light are represented.

Key Vocabulary

Wavelength	The distance between successive crests of a wave, especially points in the electromagnetic wave, such as light. Different wavelengths correspond to different colors.
Absorption	The process by which a material takes in light energy, converting it into other forms of energy, such as heat.
Transmission	The process by which light passes through a material without being absorbed or reflected.
Reflection	The bouncing of light off the surface of an object. The color we see is often the light that is reflected.
Visible Spectrum	The portion of the electromagnetic spectrum that is visible to the human eye, consisting of the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet.

Watch Out for These Misconceptions

Common Misconception

Students think a red object produces or contains red light.

What to Teach Instead

Objects do not produce or contain colored light -- they selectively reflect certain wavelengths from white light that hits them. A red apple reflects red wavelengths and absorbs the rest. In darkness or under monochromatic light of a different color, the apple does not appear red. Active experiments with colored lights help students discover this; it is nearly impossible to convey convincingly through description alone.

Common Misconception

Students believe mixing colored lights works like mixing paint -- that red and green make brown or a darker color.

What to Teach Instead

Mixing light is additive: combining red, green, and blue light makes white light. Mixing paint is subtractive: each pigment absorbs additional wavelengths, so more pigments produce darker, muller colors. The physical mechanism is different. Demonstrating both side-by-side -- light mixing on a screen and paint mixing on paper -- makes the contrast immediate and memorable.

Common Misconception

Students think white objects reflect all light and black objects absorb all light with no exceptions.

What to Teach Instead

This is accurate for ideal cases but real white and black objects deviate somewhat. More importantly, the principle needs nuance: 'white' means reflecting all visible wavelengths approximately equally; 'black' means absorbing them. An object that appears white in visible light might absorb or reflect differently in infrared or UV. This connects back to the full electromagnetic spectrum and why different sensors see different colors in the same scene.

Active Learning Ideas

Collaborative Problem-Solving: Colored Filters and Objects

Students place colored cellophane filters over a white light source and illuminate objects of different colors. They record what color each object appears under each filter, then write a rule explaining which wavelengths the filter transmits and which wavelengths the object reflects. A red filter over a blue object is the key test case that challenges intuition.

40 min·Pairs

Demonstration + Prediction: Additive Color Mixing

Using three flashlights with red, green, and blue filters (or a color-mixing LED board), project circles of colored light that overlap. Students first predict what color the overlapping regions will be, record predictions, then observe the actual result. The class discusses how this differs from mixing paint, building toward the distinction between additive and subtractive mixing.

25 min·Whole Class

Think-Pair-Share: Why Is the Sky Blue?

Students individually write a hypothesis for why the sky is blue and sunsets are red/orange, then compare with a partner. Groups share explanations, and the teacher guides the class toward the concept of differential scattering of wavelengths -- shorter wavelengths scatter more. This connects absorption and transmission principles to a familiar, visible phenomenon.

20 min·Pairs

Concept Mapping: Absorption, Reflection, Transmission

In small groups, students create a concept map connecting the terms: opaque, transparent, translucent, absorbed, reflected, transmitted, wavelength, and color. They must include at least one everyday object example for each connection. Groups share maps on the board and the class identifies common structures and resolves any conflicting connections.

30 min·Small Groups

Real-World Connections

• Stage lighting designers use colored gels and filters to control the colors projected onto a stage, influencing the mood and focus of a performance. They must understand how different colors of light mix to create specific visual effects.
• Manufacturers of paints, dyes, and pigments utilize principles of light absorption and reflection to create specific colors for products ranging from automobiles to clothing. The choice of pigments directly impacts how the final product appears under various lighting conditions.
• Opticians and lens manufacturers design eyeglasses and camera lenses that selectively transmit or block certain wavelengths of light. This is crucial for correcting vision problems or enhancing image quality by filtering out glare or specific colors.

Assessment Ideas

Exit Ticket

Provide students with a red piece of construction paper and a green filter. Ask them to write: 1. What color light does the red paper absorb most? 2. What color light does the red paper transmit or reflect most? 3. What color will the red paper appear when viewed through the green filter? Explain why.

Quick Check

Present students with three flashlights: one with a red filter, one with a blue filter, and one with a green filter. Ask them to predict what color will be produced when they shine the red and blue lights together. Then, have them test their prediction and explain the observed result using the terms absorption, transmission, and reflection.

Discussion Prompt

Pose the question: 'Why does a white shirt appear white under sunlight, but might look slightly yellow under a warm incandescent bulb?' Guide students to discuss how the spectrum of light emitted by different sources affects the wavelengths that are absorbed, transmitted, or reflected by the shirt's material.

Frequently Asked Questions

Why do objects appear to have color?

Objects appear colored because they selectively absorb some wavelengths of light and reflect others back to our eyes. A yellow banana absorbs blue and violet wavelengths and reflects red and green, which our brain combines as yellow. A white object reflects all visible wavelengths roughly equally; a black object absorbs nearly all of them. The color we perceive depends on what light is available and which wavelengths the object reflects.

What happens to an object's color under colored light?

An object can only reflect wavelengths that are present in the incoming light. A red apple under red light still appears red because red wavelengths are available to reflect. But under blue light, the apple appears black -- there are no red wavelengths to reflect, so it absorbs the blue light and reflects nothing visible. This is why stage lighting can make costumes change apparent color dramatically.

What is the difference between additive and subtractive color mixing?

Additive mixing combines light of different wavelengths: red + green + blue light creates white. This is how screens and stage lights work. Subtractive mixing combines pigments, each of which absorbs certain wavelengths: mixing paint removes wavelengths from the total, producing darker results. Cyan, magenta, and yellow are the primary subtractive colors used in printing for this reason.

How does active learning help students understand light absorption and color?

Color perception is deeply intuitive but the physics behind it is counterintuitive -- especially that objects do not contain color but rather reflect it. Experiments with colored filters, where students predict and then observe what a red object looks like under blue light, create the cognitive conflict that drives genuine conceptual change. Students who have seen an apple go black under a blue filter have an experience that anchors the correct model far better than any diagram.