ALEX Lesson Plan

How does light affect sight?  In this lesson, students will observe how light reflects off objects and into the eye so we can see.  They will learn how the pupil controls the amount of light entering the eye, how we perceive color by sensing different wavelengths of light, and why objects look different in bright and dim light.

This lesson results from a collaboration between the Alabama State Department of Education and ASTA.

• Flashlight for every 2 – 4 students
• Five colors of construction paper cut in approximately 2” by 11” strips (Use a paper cutter to cut a standard piece of construction paper into 4-5 strips. Each child needs a strip of each color.)  
• Science notebooks or note-taking guides from Attachments section
• pencils
• marker board, chart paper, or interactive white board for recording student responses
• sticky notes
• scissors for each student

Optional acceleration materials:

• copies of Electromagnetic Spectrum handout for each student (included in Attachments section)
• red, orange, yellow, green, blue, indigo, and violet yarn or paint
• glue for each student (if using yarn) or paintbrushes (if using paint)

• Computers with Internet access to How Light Affects Sight. This website provides to access all the student technology resources listed in this lesson. 
• Projector 
• Sample student illustration for evaluating student responses
• Rubric for evaluating student responses (Search for rubric 2636686 if the rubric does not automatically link.)

We cannot see without light.  When our eyes adjust to a darkened room and we begin to see more, it is because our pupils dilate to allow more light to enter them.  However, we cannot see without light reflecting off an object into our eyes.  When light reflects off an object, some of the wavelengths may be absorbed while others are reflected.  We can only see the colors of the reflected wavelengths because those are the wavelengths that enter our eyes.  These wavelengths are detected by special cells in our eyes called cones, and then they are interpreted by the brain as color.

Light travels in waves in a straight line unless an object changes the direction of the light through reflection or refraction.  The colors we see as the visible spectrum are a result of the way our brains interpret differences in wavelength of light.  Red light has the longest wavelength, which means it has the least amount of energy of any color in the visible spectrum.  Violet light has the shortest wavelength and the most energy.  The colors of the visible spectrum (red, orange, yellow, green, blue, indigo, and violet) always appear in order in a rainbow because a prism breaks the white light into its component colors from the least to the greatest amount of energy.  

For more information, check out these websites:

• Science Learn.org 
• American Optometric Association

Engage (10 minutes):

1. Have students work with a partner to observe each other’s eyes, using words to describe the parts and characteristics such as color.   Have students create a word web in their science notebooks about eyes listing these descriptive terms.  (See Attachments section below for sample word web.)  Have partners share their observations with the class and create a class word web on the board.
2. Have one partner close and cover his eyes for 10 seconds.  When the student opens his eyes, the partner should observe and describe how his pupils changed (they got bigger). Repeat this procedure with the second partner.  Ask students why they think this happened.
3. Have students add ideas to their word webs, noting questions they have about eyes and pupils underneath the web.  Tell students that they should jot the answers to their questions as they find out the answers during the lesson.
4. Create a class question and answer chart (see Attachments section for an example).  Have each set of partners write down one question they both have on a sticky note and place this on the chart in the questions column.  The teacher should refer to these questions throughout the lesson, pointing out when investigations reveal the answer and/or referring students to add answers as they conduct research on the How Light Affects Sight website during the "Explain" portion of the lesson.
5. Ask students to think of a time their vision changed when going from a light environment to a dark environment (such as coming into a room with the curtains drawn after being outside) or a dark environment to a light environment (coming out of a dark movie theater into the sunlight). What happened to their vision? What happens to their pupils? Why do they think that happened? Have students write questions or "I wonder" statements to their notebooks. 

Explore (15 minutes):

1. Give each student 5 strips of construction paper (different colors).  Have them snip each strip into 2” squares. 
2. Have students shuffle their squares and tell them they will be sorting the squares into 5 different stacks by color as quickly as possible.
3. Say “Go” and give students 10 – 15 seconds to sort their squares.  Ask students whether this task was difficult or easy and why.
4. Tell students you are going to make the task more challenging.  Have them shuffle the squares again.  Darken the room as much as possible.  (You may need to hang additional sheets or paper over blinds to limit the amount of light coming in through the windows.)  Give the students the same amount of time to sort their squares.  Were there any mistakes, or were students unable to finish the task?  Why?
5. Explain that you know they need light to see so, this time, they will have flashlights.  Have students work in pairs.  One partner will be the flashlight holder while the other sorts the paper squares by color.  Darken the room and have the flashlight holders aim the flashlight at their partner’s nose.  (This will be too much light for the student to see comfortably without shining light directly into the child’s eyes.)  Repeat the task.  Was the student successful in sorting?  Why or why not?  What did the flashlight holder notice about their partner's pupils when the light was pointed at his or her nose?
6. Ask students how we could use the flashlight to complete the sorting task more efficiently (shine the light on the squares, not in the person’s eyes).  Try their suggestions.  Have students discuss how light affects their ability to see. (Light must bounce off an object and into their eyes for them to be able to see it.  They cannot see an object without light, and they also cannot see an object if light goes straight to their eyes without reflecting off the object.)

Explain (40 - 60 minutes):

Depending on the availability of technology and the needs of your students, you may want students to work individually or in pairs at computers, or you may want to project the How Light Affects Sight website for whole-class viewing and discussion.  This site contains links to videos about sight, interactive animations about the eye, and explanations of optical illusions. As students watch the videos and animations, they should write answers to their initial questions in their science notebooks.  If they find the answer to a question written on the class question chart, they should write the answer on another sticky note and post it in the answers section on the class chart.

Elaborate (15 - 20 minutes):

1. Remind students about the seeing in the dark activity in the “Explore” phase of the lesson and have them describe how seeing in dim lighting is different from seeing in bright light. 
2. Display or distribute printed copies of the article and infographic from Live Science.  Discuss wavelengths and how our eyes detect some wavelengths of the electromagnetic spectrum but not others.  We can see light, but we cannot see x-rays, microwaves, or radio waves.  Have partners or small groups discuss these questions and jot down their answers in their science notebooks based on evidence from the article and infographic.
   
   • Why do colors look different in dim light than they do in bright light? 
   • Which cells in our eyes help us to detect color?
   • We cannot see any colors in complete darkness.  Does that mean the colors are not there, or just that we cannot see them?
   • Do all people see the same colors? Do animals see the same colors as people?
   • Why do bananas look yellow?
3. Students should continue to post answers to questions on the class question chart using sticky notes as appropriate.

Evaluation: Have students draw and label a diagram of how an object can be seen when light reflected from its surface enters the eyes.  Instruct students to include a light source, object, and eyes.  They should draw arrows to show the direction the light travels, and they may include color if they choose.  A sample illustration is included here.  After constructing the model, students should write a paragraph to explain how light helps us see.  Use the rubric to evaluate student responses.

Acceleration (optional activities for increasing rigor):

• Have students investigate how and why devices cause eye strain.  They should relate their findings about blue light to their understanding of the way light enters our eyes.  Websites for research include CBS News, Vision Council Info-graphic on Digital Eye Strain, and Kids and Computer Eye Strain article.  There are computer glasses that block some of this light, and students can engage in a debate over whether they feel these glasses are helpful or necessary based on the evidence they collect.
• Have students research the similarities and differences in color perception among animals and individuals with color blindness. People who are colorblind may not be able to detect the difference in every wavelength of light, so there may be some colors that look alike to them. Color Matters has a good article about animal vision, and there are several online color blindness tests students may wish to investigate.  Students can then present their findings to the class through a book, digital presentation, or poster.
• Have students read about the electromagnetic spectrum (see handout in the Attachments section) and construct a model of the wavelengths of the different colors of light using yarn (using the Visible Spectrum handout included in the Attachments section).  Have them measure yarn to create the waves for each color.  (If yarn is not available, they can also trace these wavelengths with paint or markers.) Students may also use the yarn to model what happens when we see an object in the classroom.  All the wavelengths of light hit the object in the form of white light.  All the different wavelengths or colors of light are included in white light, so stretch all the colors of yarn from a flashlight to the object.  All objects (except for mirrors or other objects that reflect all light rays) absorb some light rays and reflect others. The light that is reflected from the object to your eyes is how your brain perceives color. Stretch the color of yarn that matches the object from the object to your eye.  Ask students why white and black are not in the rainbow and explain that we see white when all the colors or wavelengths of light are reflected and black when all the colors of light are absorbed.

Intervention:  The following strategies may be helpful for students struggling with the science concepts, fine motor skills required for drawing the diagram, or note-taking:

• Show the videos from the  How Light Affects Sight website in small groups, so you can pause them and discuss confusing concepts at appropriate points. 
• Give students the note-taking guide (see Attachments section) to guide their work in their notebooks.
• Install and use the Readability extension in your web browser when displaying text or preparing Live Science article for printing. This extension will remove the ads and distracting material from the webpage, making it easier for students to concentrate on the important information.
• Provide clip art for students with drawing difficulties to cut and paste in creating a diagram.  Sample clip art is included as the second page of the note-taking guide in the attachment section.