You name: ______________________________
Your group members: _____________________
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Today we are continuing our month-long investigation of the efficacy of tracking plant health using infrared light (a form of light invisible to the human eye) and visible light. In our last lesson, we learned about the wetland loss occurring in the Gulf and the importance of protecting these lands.
Today, we’re going to study light, and how we see light, so that we can learn more about how to observe and protect our environment around us.
PRE-ACTIVITY QUESTION (individually)
Question 1: Summarize all that you learned from the first set of activities (“Wetlands, water, and oil)”.
I. ELECTROMAGNETIC SPECTRUM (individually)
Question 2: What is light?
Question 3: You may have heard of the term “visible light”- does that mean there is also
“invisible light”? Explain.
Question 4: What other types of light are there?

Light is electromagnetic radiation that is visible to the human eye. Electromagnetic radiation that is outside the visible range has a wavelength that is too long or too short for the human eye to detect.
Humans can only see a small portion of the electromagnetic spectrum!
The electromagnetic spectrum:
Electromagnetic radiation is classified by its wavelength. The human eye can typically see wavelengths between approximately 400-700 nanometers, but this range is just a small fraction of the entire spectrum. Below 400 nanometers is ultra-violet, or UV, light, X rays, and gamma rays. Above
700 nanometers is Infrared, or IR, microwave, radio waves, and long radio waves. Today we will be taking a closer look at visible light, as well as IR light that is very near the visible light spectrum, also known as near-infrared.
Visible light is made up of all the colors of the rainbow- red, orange, yellow, green, blue, and purple.
When all these colors combine, we see “white light”.
II. COLORED BOXES (as a group)
Materials per group
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Boxes (in which you will cut out a viewer)
Small colored objects
Red filter
 Flashlight
 Filtered light worksheet
 Scissors
Question 5: When we look at an object, why does it look a certain color?
Question 6: Why do white objects look white? What about black objects?

When light hits an object, the object will either absorb or re-emit that light. The color of an object is just a combination of all the wavelengths of light that were re-emitted by the object. A red object appears red because it is absorbing the orange, yellow, green, blue, and purple wavelengths, and is reemitting the red wavelengths. White objects are reflecting all wavelengths of visible light. Black objects are absorbing all wavelengths of visible light.
Complete Section A of “Explorations of Color.”
Next, using scissors, cut a small hole in the side of your box. This hole should be approximately 3-4” by 3-4”. This hole will serve as your “viewer.” You will be shining the flashlight through the red filter and into the box to look at different objects. Only the red wavelengths of light are able to pass through this filter.
Question 7: What do you think happens to light as it enters this filter?
Now turned to the selection of colored objects at your table, including a red, black, and white object.
In Section B of “Explorations of Color” make a prediction about what color four of these objects will appear as when viewed through the red filter. Then, individually place each of the objects in the box and use the flashlight to shine through the filter and view your objects one at a time. After doing so, record your results by returning to Section B and completing the answer blanks labeled “Actual.”
Question 8: Why did each object appear as it did both with and without the red filter?
III. MIXING LIGHT (as a group)
Materials per group
 3 Flashlights
 Squares of colored film (blue, red, and green)
 White paper
 “Explorations of Color” worksheet
You likely learned about mixing colors when you were in elementary school. However, most of our experience with mixing colors usually comes from mixing pigments. This is very different from the results of mixing light. For example, when you mix all colors of the rainbow with paint, you get a

lovely shade of brownish black. However, when you mix all colors of the rainbow in light, you get white light.
We are going to experiment with mixing light using the colored film and flashlights at your table.
First, complete the top half of Section C of “Explorations of Color” to predict what color will form when you mix each of the colors of light, and what color will form when mixing all three colors.
Then, be sure the light in the room is dimmed, without much sunlight. Place a colored film on each flashlight and shine it onto the white piece of paper. Begin by mixing two colors at a time, then all three colors at once. Record your results by completing the bottom half of Section C of “Explorations of Color.”
After you have completed Section C of “Explorations of Color,” check your work:
You should have observed that mixing red and green light results in yellow light, mixing red and blue results in magenta, and mixing green and blue results in cyan. Mixing all three results in white light.
These three colors of light are known as the primary colors because when they combine they can create all other colors of light.
IV. BIOLOGY OF OUR EYES (individually)

We now know how visible light can be reflected or absorbed and combined to form different colors.
Our eyes have millions of light-receptor cells of two types: rods and cones. Each of these types has a very different purpose. Cones can detect color, while rods cannot. Rods are extremely sensitive and can detect light at very low levels. If you’ve looked around a dark room, chances are there was still enough light for you to make out different objects, but not enough light to tell what color the objects were. This is because at low levels of light, only your rods are active.
Cones need a much greater amount of light to activate. There are three types of cone cells -- those that respond to long wavelengths, medium wavelengths, and short wavelengths. These allow us to see red, green, and blue light. We know from our light mixing experiment that these three colors of light can be mixed in different amounts to produce all other colors of light.
Color is the way that our eyes interpret the visible spectrum of light. By dividing the spectrum up among three different colors and looking at the differences between the responses of the three different color sensors, we can identify light's position on the visible spectrum. The ideal way to do this would be to get three perfectly clear, even divisions of the spectrum, like this:
But we don't have an ideal vision system, we have roughly 120 million high-sensitivity black and white photoreceptors called rods, and a more recently evolved color system six million cones. These different sensors neither divide the spectrum up evenly, nor are they of equal sensitivity. They look more like this (with the grey line showing what section of the spectrum the rods can absorb):

Notice how the rods are not sensitive to light in the orange/red range. This is why red light is used at night -- it does not interfere with your rods and therefore doesn’t destroy your night vision.
The images that we see are not a raw feed from our eyes. Our brain's visual cortex system uses complex comparisons of the relative intensity of colors to get an idea of an idealized color, such as
"red" across a wide variety of lighting conditions, even if the actual spectral profile of a specific object changes. This means the spectrum as our brain interprets it is more like this:
The normalized intensities of the different cones in our eyes, and the complex determination of relative color and brightness gives us the magnificent flexible vision system that we take for granted.
In creating film and now digital cameras, people have had to do some hard thinking about how to

make images that see color the way we do, so that color reproduction is consistent across lighting conditions.
Question 9: Given the information you read in “IV. BIOLOGY OF OUR EYES,” above, provide a summary of how our eyes detect colors.
V. OPTICAL ILLUSIONS (individually, or in groups)
Materials per student
 White Paper
 Markers
The image below is an optical illusion. Stare at the middle of the image for one full minute, and then look at the blank white paper. You will observe an after-image on the white paper that has different colors from the original image.
Question 10: What did you observe? Why do you think you see the same image when you look away?

Question 11: Were the colors the same in the afterimage as they were in the original image? Explain.
What you observed when you looked at the white paper is called an afterimage. You may have seen this effect before if you’ve experienced seeing spots of lights in your vision after looking at a camera flash. This happens because the rods and cones in your eyes lose sensitivity if they are over stimulated.
As you (probably) noted in your answer to Question 11, the colors in the image and afterimage were not the same. Your task now is to figure out how the colors in the afterimage are related to the colors in the original image, and why they appear different. You can use the markers and white paper to test various colors and make your own optical illusions to help you collect more data. Discuss with other groups to help discover the pattern.
Question 12: How are the colors in a given afterimage related to its original image?
Complete the following table:
Original
Color black
Afterimage
Color red blue green yellow magenta cyan
Having completed Question 12, refer to refer to the color wheel of light that you created in the second half of Section C of “Explorations of Light” (or refer to the color wheel in Part III of this packet).
Notice the pattern in the colors of the afterimage: The afterimage is of a color across the color wheel from the original color. For example, if the original image is green, the afterimage will be magenta.
This is because the green photoreceptors are fatigued, making the signal from the red and blue photoreceptors stronger by comparison. Sensing red and blue light together forms a magenta image.
Similarly, an original yellow image is made from both red and green light. As the cones that sense red and green are fatigued, the blue photoreceptors are stronger by comparison and create a blue afterimage.
Finally, create your own optical illusion, keeping in mind what colors the afterimage will appear.
Trade your picture with a neighbor and view their optical illusion.

Question 13: Describe the optical illusion of the person with whom you traded. What did the original image look like? What did the afterimage look like?
VI. DETECTING SHADES (individually or in groups)
Materials
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Shades of Grey optical illusion
Scissors
Question 14: Examine the “Shades of Grey” handout, and describe it in the space below.
Include specific information about the shades of grey and how they appear to change.
Using scissors, cut out the middle bar of “Shades of Grey”.
Question 15: After cutting out the middle bar, what did you observe?
In Question 15, you should have observed that the entire bar is actually one shade of grey. Although the shades appear very different, they are actually the same. Our eyes view shades of color in relation to what is surrounding the color we’re looking at. It can be very difficult for our eyes to distinguish between two different shades, or to tell that two shades are the same or different. When viewing an image of trees, lakes, and grass, it can be hard for our eyes to pick out which shade of green belongs to each. To help separate shades that are very similar, we can use something called psuedo color or false color on images.
With false color images, the three channels that a camera sees (red, blue, and green), are replaced with other colors or even with energy outside of the visible range. For example, the blue channel in a photograph can be altered to show red, and the red channel can be made to show infrared. These ways of viewing colors and other information from images can help our eyes separate shades that look similar.
Psuedo color images are similar but use only one channel of data. A popular example of a pseudo color image is in thermal images. Using only one input (temperature), a colorful image is created with higher temperatures assigned certain colors, and lower temperatures assigned other colors.

For example, look at this image with regular colors: it can hard to tell apart the water from the trees.
Try to find all the lakes and rivers.
Now examine this false color version of this same image. Try to find all the lakes and rivers, especially the smaller ones that blend in with the green of the trees.

Using false color, we can immediately see where the water is and where the trees are. This technique can help us quickly identify all the shades that are the same, while eliminating confusion from comparing shades that are next to each other.
In our next lesson, we’ll learn how we can use this technique, along with all the information we learned today, to monitor the health of the wetlands.
VII. WRAP UP
Question 16: What is the electromagnetic spectrum and how much of it can humans see?
Question 17: How do we see visible light?
Question 18: Why might we need to use false color or pseudo color images?
Question 19: What surprised you about today’s lesson?
Question 20: What would you like to learn more about from today’s lesson?
VIII. FEEDBACK
Question 21: What portion(s) of this activity did you find most engaging/informative?

Question 22: What portion(s) of this activity did you find to be problematic/not engaging/uninformative?
VOCABULARY
Rods: Cells in the retina of the eye that provide side vision and the ability to see objects in dim light
(night vision).
Cones: Cells in the retina of the eye that provide sharp central vision and color vision.
Electromagnetic Spectrum: The range of wavelengths of electromagnetic radiation extending from gamma rays to the longest radio waves and including visible light.
Infrared: Electromagnetic radiation having a wavelength just greater than that of the red end of the visible light spectrum but less than that of microwaves. Infrared radiation has a wavelength from about 800 nm to 1 mm, and is emitted particularly by heated objects.
Near-infrared: The part of the infrared spectrum that is closest to visible light.
Afterimage: An impression (usually a visual image) retained after the stimulus has ceased.
Photoreceptors: A nerve ending, cell, or group of cells specialized to sense or receive light.
False Color: A false color image does not use the natural colors (what’s called a true-color image).
Instead, it assigns other colors to each channel in order to ease the detection of features that are not otherwise easy to see. This could involve changing visible colors, IR, or other data channels. For example, false color images depicting near infrared data are used for the detection of vegetation.
Pseudo Color: An image that uses one channel of data, such as temperature, elevation, etc, and assigns each intensity value a color. It is similar to false color images, but differs in that it uses a single channel of data, while false color images are commonly used to display three channels of data.