Bio A – Energy
The Science of Light Energy and Color
Energy comes in many different forms. Light is one form of energy that is particularly important to living things.
Without the light energy from the sun, life on earth would not exist.
The energy from the sun spans a wide range or spectrum called the electromagnetic spectrum. The EM spectrum is
shown below. It includes everything from radio waves to Gamma rays.
Purple: 380 – 440
Yellow 590 – 620
Blue: 440 – 520
Orange – 620 – 660
Overlap blue/green 500 - 520
Orange red 660-680
Green 520 – 550
Yellow Green 550 – 590
Red 680 - 740
Bio A – Energy
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When light hits an object one of three things happens:
o The light is absorbed by the object. Light that is absorbed cannot be seen by our eyes.
o The light is transmitted, or passes, through the object
o The light is reflected, meaning the light bounces off the object and hits your eye. The wavelength of the
light that bounces off will determine the color of the object.
Different wavelengths of light can combine to form different colors. A light that emits (gives off) wavelengths of 400nm
(blue) and 600nm (yellow) will look green because the two lights mix together. The sun emits all wavelengths in the
visible light spectrum. They all combine together and look white. But REALLY they are many different colors of light
together. If the sun’s light shines through a prism or a raindrop, each wavelength is bent at a slight different angle,
separating them all out so we can see them individually. This is what makes a rainbow!
So back to that shirt. Since you are sitting in a room with white light, your shirt is being hit with all colors of the rainbow.
Depending on the material and dyes used to make your shirt, some light might be reflected. This is what we are seeing.
In today’s activity we’re going to examine a few different types of light to see what wavelengths are really being
emitted. Look at each type of light through the spectroscope and draw the bands underneath the correct place on the
scale using a colored pencil of the right color. Be sure to draw your bands the approximate thickness that you see them.
Use the scale inside the spectroscope to help you measure.
Bio A – Energy
Fill in the colors you ABOVE each grid at the appropriate wavelength. Refer to the colors shown on the “wavelength” “
picture (first page of your lab) that is sitting on the lab table. Darken those colors which show a high “brightness”. Make
sure colors are “discontinuous” or continuous (whatever you see). Try to place the NARROW slit directly in front of the
light source (with the color spectrum NOT on the light source, in order to see a clear grid. If you see two “rainbows” try
moving the spectrometer to clearly see only one.
The single numbers (4,5,6,7) represent 400 – 700 nm wavelengths. Be sure to note which wavelengths are red and wich
are green or purple (etc.) The wavelengths (short to long) go VIBGYOR (backward ROYGBIV). Look for key differences
between the light sources!
Fluorescent Room lights:
___________ colored light bulb (fill in the color you
have chosen):
“Daylight” light bulb:
Black light bulb: (be sure this is actually done when the
lights are out)
LED Bulb
Sun (if it is out… Don’t stare too long or directly at it!)
Bio A – Energy
Discussion Questions:
1. Create a table showing the differences in the spectra for the various light sources.
Light Source:
Major wavelengths seen
Fluorescent
Daylight
LED
Colored Fluorescent (List
color)
Black Light
Sun
2. Which spectrum literally has “all visible colors”?
Continuous or Discontinous
spectrum
Colors that are INTENSE
Bio A – Energy
3. The colors in the light spectrum have different wavelengths. The shorter the wavelength, the greater the
energy. Which color in the spectrum has the most energy and which has the least amount of energy?
4. Besides visible light, what are other types of energy that make up the electromagnetic spectrum?
5. Can plants grow with other types of energy from the electromagnetic spectrum, such as microwave radiation if
they do not receive energy in the visible light spectrum? Why or why not?
6. When an object appears a certain color, the object is reflecting those wavelengths of light and absorbing the
colors that you do not see. What is the main color of the light spectrum that most plants reflect?
7. The sun emits white light. Explain what colors make up white light.
8. You are walking down the sidewalk in bare feet during a sunny summer day. The light colored concrete is warm,
but tolerable. You get to an intersection and step into the black asphalt street. Immediately you start hopping
around like a cartoon character as smoke rises from your burning feet. Why was the asphalt so much hotter
than the concrete when both were in the sun?
9. A similar graph can be made for pigments BUT instead of showing the light energy being emitted (pigments are
not lights!) they show what wavelengths of light and how much of each a pigment can absorb. Below is a graph
showing the percentage absorption of different wavelengths by chlorophyll a. (they were bad and didn’t label
their Y axis but it should say “% absorbed”)
10. Use your colored pencils and the “guidelines” for color (page 1) to color in this graph
Bio A – Energy
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If we only had single color bulbs to grow our plants, what wavelength would we want it to be and why? Hint, use
the absorption graph to help you make your decision. The more absorption, the more photosynthesis will take
place.
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Which wavelength bulb would basically be like growing the plant in the dark? Why?
11. Describe what you think would happen if you grew a plant in EACH of the light sources that you looked at in this
lab. In which light source would the plant grow the best? Why? EXPLAIN!!!