To introduce the roles of the eye and brain in the perception of objects, including color.
Many middle-school students do not think of light as something that travels from one place to another, and most tend to identify light with its source (e.g., light is in the bulb) or its effects (e.g., a patch of light). As a result, students have difficulty explaining the direction and formation of shadows, as well as reflection of light by objects.
Middle-school students usually understand that mirrors reflect light, but have a hard time believing that of objects which do not reflect their image. Many students do not believe that their eyes actually receive light when looking at an object. Students' ideas of vision vary from the notion that light fills space and the eye sees without anything linking it to the object, to the idea that light illuminates surfaces that we can see by the action of our eyes upon them. The notion that the eye can see without a link to the object is a notion that can even persist after basic instruction in optics. (Benchmarks for Science Literacy, pp. 338-339.)
There are three Science NetLinks lessons in this series on light:
Light 1: This lesson is an introduction to light, preparing students to address issues like those discussed above. This lesson introduces students to the electromagnetic spectrum (focusing on visible light) and the wave nature of light.
Light 2: This lesson focuses on the idea that we can see objects because they either emit or reflect light. It discusses the way light is reflected, absorbed, and scattered to allow certain wavelengths to reach the eye, leading to a perception of different colors.
Light 3: This lesson includes an Internet exploration that focuses on the roles of the eye and brain in the perception of color. It includes an introduction to the anatomy of the eye, including the functions of rods and cones.
Ask the following questions to generate student interest in this lesson, as well as review basic concepts:
- What are some "sources" of light? (Examples include the sun, fluorescent lights, and incandescent bulbs.)
- Have you ever noticed that objects look different colors in different light? (For example, a fluorescent bulb produces a bluish colored light while an incandescent bulb produces reddish light.)
- In what ways can light be reflected when it hits a surface? (If the surface is smooth, the light is reflected at the same angle it came in. If the surface is rough, the light is scattered in all directions. When the surface is somewhere in-between, it reflects light close to the same angle it came in.)
- Is anyone colorblind?
- If you have ever watched the sun set, you may have noticed that as it gets darker, it becomes more difficult to distinguish the colors of the objects around you. What might cause the colors to be less distinct? (As there is less light from the sun, less light is reflected from the surfaces around you. Therefore, your eyes are less able to distinguish color.)
In this section, students will read information online and answer questions on the student sheet, All Those Seeing Color, Say Eye! Depending on the number of available computers, students could work alone or in small groups.
Distribute the student sheet and have students complete Part I. As outlined on the student sheet, students will view a slideshow, An Eye on Color, from The Tech Museum of Innovation, and answer questions.
After students finish, discuss the questions listed on the student sheet in class:
- What happens when waves of light enter your eye? Discuss the role of the pupil, retina, and optic nerve. (Light comes in through the pupil and splashes inside your eye on the retina. Optic nerves carry information about the light to your brain.)
- Where are rods and cones located? (Retina.)
- What are rods and cones? What do they allow you to see? (Rods let you see black and white only; cones let you see color.)
- In what area of the retina are cones concentrated? (Center.)
- When do cones work best? (When there's a lot of light, like during the day.)
- In what area of the retina are rods concentrated? (Edge.)
- When do rods work best? (In dim light, like late in the evening.)
- You've just read what happens in the eye: light goes through the pupil, then hits the rods and cones and causes a chemical reaction. What understands this reaction and carries the message to the brain? (Optic nerve.)
- What causes the blind spot? (You don't have rods or cones where the optic nerve connects to your retina; there you have a blind spot. You can't see light that hits your blind spot.)
- Why do certain animals (like the owl and bee) see colors differently than humans? (They have different cones.)
Now have students complete Part II on the student sheet. This requires students to continue their exploration of the eye, light, and color. They'll read in more detail about the anatomy of the eye, optic nerve, and how messages are transmitted to the brain.
When they are finished, discuss the questions on the student sheet in class:
- What are functions of the eyelid and blinking? (Blinking allows the eyelid to help keep the eye clean.)
- What is a function of eyelashes? (Eyelashes work with the eyelid to keep dirt and other stuff out of the eye.)
- Draw a diagram of the eye labeling the sclera, cornea, iris, and pupil.
- What part of the eye lets light in? (Pupil.)
- What happens to the pupil as you enter a dark room? Why? (It gets larger, in order to let more light in.)
- Once light enters through the pupil, what part of the eye focuses light on the retina? (Lens.)
- What carries messages from the eye to the brain? (Optic nerve.)
Use the student sheets and class discussions to assess student understanding. In addition, have students draw a diagram illustrating the movement of light from outside the eye, into the eye, and finally to the brain. Have students label at least the following in their diagrams: light source, object that is seen, pupil, lens, retina, rods, cones, optic nerve, and brain.
The Science NetLinks lesson Nearsightedness gives students an opportunity to examine the nature of scientific research in the context of research pertaining to myopia, or nearsightedness.
The National Eye Institute has educational materials for kids, available in PDF format. Find teaching tools, materials on how the eye works, common vision disorders and diseases, and eye safety.