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Light and Color

This activity is designed for grades K-3 and is expected to take 1-2 hours. The lesson plan consists of several short activities which complement each other but are independent of each other. If student response to an earlier part of the lesson is enthusiastic, go ahead and spend extra time on that activity. Don't worry about needing to "cover the material." On the other hand, this lesson plan was put together with very young children, and hence very short attention spans, in mind. This way, if one activity does not hold the students' interest, you can move quickly on to the others.

Guiding Questions

What is light?
What do we mean by "optics?"
Where does light come from?
What can we learn by looking at light?
What occupations involve using or studying light?

Objectives

Learn that every day white light contains many colors, through the use of prisms, diffraction gratings, and color filters.
Learn something about the way our eyes perceive light, through observation of contrasting shades, patterns and colors.
Light is a form of energy that travels through space.
Light travels in a straight line and the obstruction of lights path results in shadows.

Concepts

Energy. Energy is the capacity for work or vigorous activity. You can experience energy through the mechanical energy reqired to throw a ball, the electrical energy required to operate a flashlight or the chemical energy required to digest your food. Heat energy causes your ice cream to melt and water to boil.
Light. Light is a form of energy. It enables us to see. It comes in many different colors, red, orange, yellow, green, blue, indigo, violet, white and black.
Science. Science involves the observation, identification, description, experimental investigation and theoretical explanation of events.
Optics. Optics is a science, the science of the study of light.
Vision. Vision is the ability to see or observe events with our eyes.
Perception. Perception is how we become aware of an event and understand through the use of our senses. We sense light with our eyes and our brain interprets the light we sense with our eyes in order to perceive colors ,shapes, and the brightness of objects.

Principles

Color. Colors result from different energy levels of visible light. We see the different colors of the rainbow because each color has a different level of energy.
Color Spectra. A color spectra is a broad range of colors, such as those of a rainbow, red, orange, yellow, green, blue, indigo, and violet.
ROYGBIV. Is an acronym used to remember the colors according to their energy level. Acronyms are formed from the first letter of a group of worlds-Red,Orange, Yellow, Green, Blue, Indigo, Violet.
Brightness. The amount of light that reflects from an object.
Shade. The degree to which a color is mixed with black.
Shadow. A shadow is made when an object blocks the path of light. Your shadow on a sunny day is made because your body is blocking the path of light between the sun and the ground. Notice how the location of your shadow is different at different times of the day.
Wavelength. The distance between repeating waves of light. This distance is very short ranging from for red light to for violet light.
Primary Colors. Primary colors or Additive Primaries are the basic colors that when mixed form other colors.
Primary colors for paints. The Additive Primaries for paints are Red, Blue and Yellow. For example Blue mixed with Yellow make Green.
Primary colors for light. The Additive Primaries for light are Red, Blue and Green. For example Blue and Green make Yellow.
White Light. White light is made of, composed of all colors mixed together, ROYGBIV and all shades in between. We see white objects because white material reflects all colors of light.
Black Light. Black light is made by an object that absorbs all colors of light without reflecting any color.
Filter. filter is a object used to separate gases, liquids, or light.
Prism. A prism usually made of crystal or see through plastic separates white light into a broad range of colors, ROYGBIV.
Diffraction Grating. A diffraction grating is used to change the direction of light or to filter, to remove certain bands of light. Certain bands of light are known as colors.

Experiments

Taking Light Apart
Putting Light Together
Color Contrast
Colors and Pictures
More on Contrast
White Light Contains Many Colors

Materials

Taking Light Apart
- Halogen Lamps
- lamps (60W light bulbs)
Putting Light Together
- Construction paper or oragami paper in the following colors: yellow, purple,green, blue (two sheets), and orange (two sheets).
- Select pieces of paper of the same size.
- Paint sample cards
- Glue
Colors and Pictures
- Several different colors of different plastic (enough for each group of 3-5 students) such as acetate report covers, theatrical light filters, etc.
- Assorted colored pictures (from magazines, old wall calendars, etc.)
- Crayons, colored pencils, or colored pens
More on Contrast
White Light Contains Many Colors
- Diffraction grating for each student
- Small lamp
- 3 Extension cords
- 3 Light Sockets
- Light bulbs: one 60 W white light, plus a variety of colored 'party' lightbulbs (strings of holiday lights work well)
- A large roll of white drawing paper (or several large sheets)
- Masking tape

Room Preparation

Make sure sufficient amount of supplies are available. Provide a white movie screen or create a projection screen with sheets of white paper. Select a room with blinds or curtains that can closed to prevent external light from interfering with the project.

Safety Preparations

Make sure children remain seated when the lights are dimmed or turned off. Prevent children from touching light bulbs, especially when they are illuminated.

Introduction

Start with some open discussion about light, based on the following guiding questions.

What is light?
- Light is a form of energy. It enables us to see. It comes in many different colors. (What are some of the colors of light, an give an example for each color.) Tell them its O.K. if they don't have any ideas right now; they will learn about what light is over the next few weeks.
What do we mean by "optics"?
- Optics is a science. It is the study of light. So as we figure out what light is during the next few sessions, we will be doing optics experiments.
Where does light come from?
- Many possible answers. Try to get a range of colors among the suggested answers. Examples: the sun, white or yellow (if they say yellow, ask them to look at the sunlight coming in the window); lightbulbs, television sets, computer screens, laser, neon signs.
What can we learn from looking at light?
- The students may not have too many ideas now, but after this session they should have some ideas about:
  1. spectra: identifying elements by looking at the colors in the light that comes from a lamp—or a star
  2. we can learn about the way our eyes work by how we perceive color.

Taking Light Apart
- Discussion. Where do the different colors come from when you look at the sunlight through the prism? Do they come from the sunlight? If so, why don't we see the rainbow without the prism? Do the colors come from the prism? If so, why don't we see colors when we look at all objects with the prisms? Hopefully the students will suggest that it is the combination that makes the colors visible. The colors are 'hidden' in the sunlight, but we need the prisms to split the light apart so we can see all the colors. In viewing the different gas lamps,
  - different lamps have different colors in them
  - comparing their pictures to the keys, have the students try to identify the gases in the lamps. Have a vote to decide which is which.
Putting Light Together
1. Human Color Wheel
  - Discussion. The rules for mixing colored lights are different than the rules for mixing colored paints. In paint, the primary colors are red, blue, and yellow. We can mix any color using these three colors. For lights, the primary colors are red, blue, and green. To get yellow, we mix equal parts of red and green! After the students have arranged themselves in the color circle, ask what happens when we mix red, green, and blue. If we mix paints, we'd get grey or black. If we mix lights, we'd get white! White is a mixture of all colors. That is why we could see many colors in the (white) sunlight when we looked with the prisms.
2. Mixing Colored Lights
  - Discussion. What color is a shadow? Black, usually—in white light. But in general the color of the shadow depends on the color of lights present, and the way that they mix together.
    Colored pieces of paper appear to be different colors depending on which lights are on. You can't see red without some red light, etc. Point out the way the shadows change color with different light combinations.
3. Color Table
  - Discussion. Many colors appear different under different color filters. Lead the discussion by having the students put a line of each crayon on a piece of paper, and then put one color filter on at a time. Ask which colors change, which disappear, with each filter. Tell the students that they can use the filters to change the crayon pictures that they draw. For example, you can make a face whose smile disappears with a certain filter, or you can hide a message with alternating letters—where half of the letters disappear under a certain filter!
White Light Contains Many Colors (or, "There's a Rainbow Hidden in the Lightbulb!")
- Materials Needed
  - Diffraction grating for each Student
  - Small lamp
  - 3 Extension cords
  - 3 Light Sockets
  - Light bulbs: one 60 W white light, plus a variety of colored 'party' lightbulbs (strings of holiday lights work well)
  - A large roll of white drawing paper (or several large sheets)
  - Masking tape
- Introduction. This part of the lesson plan teaches the same concept forwards and then backwards. Students learn that they can separate white light into its components. Then, they learn that with the right mixture of colored light, they can 'reassemble' white light.
- Part I: Taking Apart White Light
  Time Duration. 10-15 minutes
  - Assembly. Set up the small lamp with the white light bulb in a central location of the room. Distribute the diffraction gratings to the students. Close the shades on any windows in the room.
  - Experiment. Turn off all other lights in the room, except the small lamp. Ask the students what color the light bulb in the lamp is, without looking through the diffraction grating. Ask what color it appears when they look through the diffraction grating. Ask where they think the colors are coming from: the lamp or the grating. If they say the grating, have them look at other objects (not necessarily other lights) and ask if they see colors appear. If they say the lamp, ask them where the other colors go when they remove the grating from their eyes. Help them conclude that the colors are always there in the lamp, and the grating helps us to see them. Point out that rainbows come out of sunlight, which also appears to be white.
- Part II: Putting White Light Back Together
  Time Duration. 20-30 minutes
  - Assembly. If a large empty space on a white wall is not available, make a screen by taping large pieces of white paper over an area of wall, or over the blackboard. Set up the bulbs so that the light from all three bulbs falls on the same area of the screen, and all bulbs are approximately the same distance from the screen. For best results, put the green bulb in between the red and blue bulbs.
  - Experiment. Turn on the colored lights and adjust the positions of the bulbs until you obtain the "whitest" light on the area of the screen where the three lights mix. Turn off the room lights, and make sure that the room is otherwise as dark as possible. Place a narrow opaque object, such as a pencil, fairly close to the screen. Adjust its distance from the screen until you see three distinct colored shadows. Remove the object, turn off one of the colored lights, and notice how the color on the screen changes. Then replace the object in front of the screen and notice the color of the shadows. Move the object close to the screen until the shadows overlap. Notice the color of these combined shadows. Repeat the previous step with a different light turned off while the other two remain on, and then a third time so that you have tried all possible combinations. Repeat again with only one light at a time, and then again with all three lights on. Vary the size of the object, and the distance from the screen. Let the students try using their hands as the object for all different light combinations.
  - Inside Information. The retina of the human eye has three receptors for colored light: one type of receptor is most sensitive to red light, one to green light, and one to blue light. Through different options of color receptors, humans are able to distinguish more than a million shades of color. When a red light, a blue light, and a green light are all shining on the screen, the screen looks white because these three colored lights stimulate all three types of color receptors in the eye approximately equally, giving the sensation of viewing white light. Red, green, and blue are called additive primaries of light. With these three lights you can make shadows of seven different colors: blue, red, green, cyan (blue-green), magenta (a mixture of the blue and red), and yellow (a mixture of the red and green). If you block two of the three lights, you get a shadow of the third color. If you block all three lights, you get a black shadow. If you block one of the three lights,you get a shadow that is mixture of the other two colors. For example, if you turn off the red light, leaving only th blue and green lights on, the lights mix and the screen appears cyan. When you hold an object in front of the cyan screen, you will see two shadows: one blue and one green. In one place your object blocks the green light, leaving a blue shadow in the other the object blocks the light coming from the blue light, leaving a green shadow. When you move the object close to the screen you will get a very dark (black) shadow, where the object blocks both lights. It may surprise the students that a red and a green light mix together to form yellow light on a white screen. A mixture of red and green light stimulates the red and green receptors on the retina. Those same receptors are stimulated by yellow light (e.g. light from the yellow part of a rainbow). Different rules apply for color mixtures using light than for color mixtures using paint.
Color Contrast: A colored object may look different against different-colored backgrounds.
- Time Duration. 10-15 minutes
- Materials
  - Construction paper or oragami paper in the following colors: yellow, purple, green, blue (two sheets), and orange (two sheets).
  - Select pieces of paper of the same size.
  - Paint sample cards
  - Glue
- Introduction. From the previous experiment, students have gained some insight concerning the perception of colors, and the way that different colors are related to each other. This experiment builds on this knowledge, by showing that the color receptors of the eye respond not only to the color of a specific object, but also to the color of the environment.
- Assembly. Cut one sheet of orange paper in half and glue it to cover up half of a blue sheet. This gives you a large sheet of paper that is half blue and half orange. This large piece of paper will be the background for other colors. Cut two small squares from each of the colors you have, including squares of blue and orange of a different shade than the large sheets. Glue these squares across from each other, one on the blue background and one on the orange background. From the same colors as the small squares, cut strips of each color to use for comparison.
- Experiment. Ask the students to compare each set of colored squares. Ask whether the squares appear to be the same or different shades; and if different, have them describe the difference. Place the comparison strips so that they touch both squares of the same color at the same time to verify that the squares really are a perfect match. Color contrast can also work in reverse: against certain backgrounds, different colors can look the same. From the paint samples, choose two shades that are very similar but are clearly distinguishable when placed next to each other. Put the paint samples on different backgrounds. Often, the slightly different colors will appear to be the same. Some experimentation (beforehand) is required to get the desired effect.
- Inside Information. The previous experiment introduced the idea that we perceive color when color receptors on the back of our eye are stimulated. Recall that there are three types of color "sensors" in our eyes: red, green, and blue sensors. When sensors in one part of the eye see blue light, they make nearby sensors less sensitive to blue. Because of this, you see a colored spot on a blue background as less blue than it actually is. For example, a purple spot on a blue background will appear less blue and more reddish than it would appear otherwise. Similarly, a spot on an orange background seems less orange than it actually is. Remember, though, that your eye can't remove any colors from a spot that weren't there in the first place. A yellow spot doesn't look any different against a blue background, because yellow doesn't contain any blue.
Colors and Pictures
- Time Duration. 20-30 minutes
- Materials
  - Several different colors of different plastic (enough for each group of 3-5 students) such as acetate report covers, theatrical light filters, etc. Assorted colored pictures (from magazines, old wall calendars, etc.) Crayons, colored pencils, or colored pens
- Introduction. This activity continues to build on the students understanding of colors as mixtures of other different colors, and the way that a color's appearance changes depending on the colors that border it. Whereas the Colored Shadow experiment demonstrates color addition, this experiment demonstrates color subtraction.
- Assembly. None required.
- Experiment. Divide the students into groups and distribute the following materials to each work station: a colored filter of each color available, several colored pictures, blank paper, and crayons or colored pens. Have the students experiment with the filters, observing how the appearance of the pictures change with each filter. Point out that with a red filter, for example, the pictures will appear to contain only black and shades of red. Show the students that they can print their name or draw a picture using several different crayons, and then make parts of the drawing "disappear" by using the filters. Encourage creative uses of this, such as writing secret messages that can be decoded with the proper filter.
- Inside Information An ideal red filter transmits only red light and absorbs (or subtracts) all other colors. Likewise, an ideal blue filter will pass only blue light, etc. In reality, most filters are not ideal filters. For example, a blue filter may pass primarily blue light, but may also allow some green light to get through. When you view a multi-colored picture through an ideal red filter, only red light will reach your eye. Red light comes from the red parts of the picture, and also from the white areas, since white light contains red. The red parts of the picture disappear since the blend in with the red light from the white parts of the picture. Any part of the picture that did not contain any red would appear black. Any color that contains some red will appear as some shade of red. You can use different filters to determine what color components make up a given shade. Note: four-color printing in magazines is done with magenta, cyan, yellow and black pigments. Different combinations of these pigments produce all the colors found in magazines.
More on Contrast: Shades of Grey
- Time Duration. 5-10 minutes
- Introduction. If time allows, this is a nice follow-up to the previous activity on color contrasts. Our perception of an object's color is not only affected by the surrounding colors, but also by the presence of sharp edges. Our visual systems are designed to be especially sensitive to areas of sharp contrast, i.e. we are very good at perceiving whether a given shade is lighter or darker than another.
- Materials.
  - One sheet of Pantone 404 u-g graduated paper (uncoated, available in art supply stores in 20" x 24" sheets.)
  - Cardboard for backing
  - A "horsetail" made of a length of yarn or twine
  - Sheet of white paper
  - Hole punch
  - Scissors
  - Glue or tape
- Assembly. Punch two holes 4" apart near the edge of a sheet of white paper and set it aside. Put the large sheet of graduated paper i front of you with the darkest side on the left. Cut a 2" strip from the right edge of the paper (the lightest side) and throw it away. Next cut a 4 inch-wide strip from the new right side. Cut this piece in half so that you have two shorter identical pieces. Place the light side of one piece next to the dark side of its twin, and mount the pieces on cardboard with glue or tape. Attach the 'horse tail' above the boundary between the two pieces so that it hangs down and covers the boundary.
- Experiment. Position the horsetail so that it covers the boundary and ask the students what they see. Most will see a uniformly grey piece of paper with a rope hanging down the middle. Lift the tail and ask again. Most will now see two uniform regions, each a different shade of grey. To show that the two sides are identical shaded regions, hold the punched piece of paper over the grey areas, with one hole over each side of the boundary. The two regions viewed through the punches will alway be the same shade of grey.
- Evaluation. Ask the children questions that show whether or not they understand the following principles:
  - Light is a form of energy that travels in a straight line through space.
  - Color results from the reflection of certain wavelengths of light from the material.
  - White light is made up of all the colors combined together.
  - Black results when all the light is absorbed by the material.
  - Shadows occur when an object blocks the path of light.
  - The primary colors are the fundamental colors which make other colors when they are combined together.
  - Our eyes are the organs which allow us to detect light.
  - Our brain forms images from the light our eyes sense. These images are our visual perception of these objects.
  - Science involves observations and experiments that allow us to understand the world around us.
  - Science experiments can be simple and fun as well as very valuable and informative.

The study of light has allowed advances in optics which we use every day. Here are some examples of how we use light to explore and understand the world around us as well as ourselves.

Public Safety
- Radar Guns
Science: Spectroscopy
- Lasers
- Microscopes
- Telescopes
Medicine
- X-Rays
- MRIs
- CTs
- Aerospace/Aeronautics
- Weather Forecasts
- Stargazing

Careers

Doctors
Engineers
Scientists
Entertainers
Astrophysicists
Astronomy
Aerospace
Engineering
Aeronautics
Biology
Bioengineering
Civil Engineers
Chemistry
Electrical Engineering
Physics
Mechanical Engineering
Medicine
Meteorology
Health Science