As we enter the 21st century, perhaps no area of science touches our lives and the lives of our students more directly than optics. We speak on the telephone without realizing that our voices have been converted into digitally-encoded flashes of light that travel over miles of thin optical fibers. Information, whether it be music, images or text, stored digitally on CDs and DVDs is recorded and retrieved optically. At concerts and sporting events, giant screens consisting of thousands of light emitting diodes provide ultra-bright, high-resolution images of figures too small to be seen on the stage or field. State of the art infrared cameras send eerie nighttime images of battles thousands of miles away to our living rooms almost instantaneously.

Our understanding of outer space as well as much of the micro-world has been gained through optical exploration. The production of the color images that appear on television, computer, and movie screens relies heavily on optical and perceptual principles. And perhaps most importantly, over 80% of the information we receive from our environment is obtained through the most marvelous optical instrument of all, the eye. The study of light and color has always been the highlight of the year for my students. Optical effects are immediate, captivating, and as we have seen, incredibly relevant to our students' daily lives. Allowing students to explore with light, and our perception of it, produces a level of engagement that has to be seen to be believed!

This collection of laboratory experiences will take your students on a journey through the world of light, color and perception. The learning cycle approach will be employed to allow your students direct experience with optical phenomena and visual perceptual mechanisms. By way of hands-on experiments, your students will learn how light may be beamed, blocked, bounced, bent and even "stored." They will find out how soot can be transformed into silver and why the myriad colors on your television screen are really just in your head. Through some visual foolery, they will experience the perceptual paradoxes that occur when the brain is unable to make sense of sensation. And in the end, find that they have learned a new way of "seeing the light."

Key Concept: The slow emission of stored energy in the form of visible light is called phosphorescence. "Glow in the Dark" phosphorescent materials with long decay times are used to cause watch dials, safety markers, and many children's toys to glow long after the lights go out.

Setup Instructions:
In a darkened room, provide students with any camera flash and a sheet of Phosphor Glow Paper. If a small fan is available, students may "freeze" the motion of the fan blades by placing the fan between the Glow Paper and the camera flash.

Station Instructions:
Turn on the flash unit. Place your hand or other object (keys, pen, etc…) on the shadow screen. Direct the flash toward the shadow screen and activate the flash. Remove the object from the screen.

Key Concept: Curved reflecting surfaces are capable of producing both real and virtual images.

Setup Instructions:
Hang a colored ball from the Virtual Reality Mirror so that the ball hangs in the center of the mirror.

Station Instructions:
Pull the colored ball attached to the silvered hemisphere towards you and release it. Watch the images produced by the concave reflecting surface. Describe the changes in the image as the ball swings back and forth and side to side.

Stop the ball and allow it to hang straight down. Where is the image now?

How does the size of the image of the ball compare to the size of the ball?

Look at your reflection in the convex (back) side of the hemisphere. How do you look?

Now hold your finger or other object in front of the convex surface. Describe the image formed. For example, is it right side up or upside down? Is it larger or smaller than the actual object?

Give some everyday uses for convex mirrors.

Key Concept:
As white light passes from one material into another, the constituent wavelengths (colors) travel at different speeds, sometimes causing the white light to break up into a spectrum of colors.

Setup Instructions:
Place a clear plastic (the clearer, the better) box of water on the overhead projector. Close or cover the top lens so that no light is projected forward out of the projector. Arrange the projector so that students can see the spectra that come out of the sides of the box.

Station Instructions:
Examine the array of colors produced by the water-filled plastic shoebox. Can you think of two things that this array of color has in common with an actual rainbow?

List the colors, starting from the inside, present in this rainbow.

How do suppose this rainbow is formed?

How is an actual rainbow formed?

Are colors originally present in white light or is the water the source of the spectral colors in both cases?

Key Concept: Anamorphic images are purposely distorted during their creation and require reflection in a cylindrical or conical mirror to make them intelligible.

These distorted pictures are examples of an art form known as anamorphosis. A small group of artists began working with anamorphic art during the Renaissance. Anamorphic drawings appear strange and almost unrecognizable to the unaided eye, while a reflecting cylinder reveals an image of normal proportions. This technique is essentially the reverse of a fun-house mirror, which creates a distorted image of a normally proportioned person.

Project:
Use the grids to create your own anamorphic art. Draw a figure of your choice on the square grid, then transfer your drawing, point by point, to the cylindrical grid. Color your work if you wish. To transform your distorted figure into a recognizable object, just look at its reflection in the cylinder!

Download the anamorphic art grid sheet

Key Concept: Dyes contained in these beads are sensitive to ultraviolet light. When exposed to UV light, they change color.

Setup Instructions:
Provide UV Beads, a small UV tube (black light), and other sources of light, including sunlight.

Station Instructions:
Examine the beads and describe their color.

Now place a few beads near the "black light" tube. What happens to the beads when they are exposed to black light?

Can you suggest an explanation for this behavior?

What happens when the beads are now longer exposed to light from the tube?

Hold the beads near a TV screen or computer monitor. If possible, take the beads outdoors so that they are exposed to sunlight. Try other sources of light. Which of these sources of light cause the beads to change color? Why do you think this happens?

Suggest an experiment that you could perform with the beads to test the effectiveness of suntan lotions.

Key Concept: Passing light waves through a polarizing filter results in light waves that vibrate in a single plane. Two polarizing filters with their polarizing axis crossed, that is, at right angles, will pass no light.

Does the ball pass through or bounce off the wall?

Can you explain this mysterious behavior?

If you are totally baffled, you may take the lid off the box. To discover why the "bogus barrier" exists, look through each of the windows with one of the square Polaroid filters provided at this station. You may find rotating the filter while looking through each window quite revealing!

Notice the direction of the polarized film panels.
Box drawing is shown without the lid on!

Image shows  a plastic fork, protractor, and an empty cassette case under the polarizing film.

Key Concept: Placing certain transparent materials, such as plastic, between two polarizing filters produces colored patterns that are indicative of stress in the material.

Key Concept: With the proper illumination, a concave face may appear convex. This is due in no small part to the expectation we have that human faces are always convex.

Key Concept: Three colors of light-generally red, green, and blue- known as the additive primaries can be mixed together to obtain any other desired color.

Setup Instructions:
Cover three gooseneck or flood lamps with red, green, and blue color filters. Attach each lamp to an adjustable power supply. (Adjustable power cords are available at home improvement centers.) Train the beams from the three lamps on a white screen so that they overlap.

Station Instructions:

Adjust the intensity of lamps until their combined effects produce white light. Red, green, and blue are called the additive primary colors. Why?

Block one lamp at a time with a piece of paper and observe the resulting color on the screen. In your own words describe the color produced in each case.

The use of color dots to form images on television or computer screens is referred to as partitive mixing. Partitive mixing relies on the eye's inability to resolve closely spaced objects. In the case of a TV screen, the objects are red, green, and blue light-emitting phosphors. Phosphors for each of the primary colors are clustered together in groups of three. In all, there are over 200,000 of these primary clusters. At a sufficient distance from a TV screen, the eye interprets each triad of colored dots as a single color.

Which phosphors are emitting light when a television screen or computer monitor is white? Black?

green + cyan = _______________

green + yellow = _______________

green + magenta =_______________

red + cyan =_______________

red + yellow =_______________

red + magenta =_______________

blue + cyan =_______________

blue + yellow =_______________

blue + magenta =_______________

red + green =_______________

red + blue = _______________

green + blue =_______________

Your observations may now be used to deduce the transmission characteristics of cyan, yellow and magenta filters. In terms of red, blue, and green, list the colors that are transmitted by each of the following filters:

cyan:______________________________

yellow:______________________________

magenta:______________________________

cyan + yellow + magenta:______________________________

Cyan, yellow, and magenta are called the "subtractive primary colors." A cyan filter may be thought of as a "minus red" filter because it absorbs red light.

What color does a yellow filter absorb?

A magenta filter?

Many times students miss some important aspect of an activity. Therefore, it is often good for the teacher to repeat some of the activities done by the students as class demonstrations. In this way the teacher can focus student attention on the essential element of selected activities. Drawing on students to explain what they see and why they think it happens gets them actively involved in a communal learning process while allowing the teacher to assess understanding.

In addition to revisiting smorgasbord activities, the teacher can further amplify basic principles through the use of novel demonstrations. These demonstrations may be used to further clarify concepts and illustrate real-world applications of the basic principles being studied.

Color Subtraction Demo