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The Effects of Different Light on Plants Brady Whisenhunt 1729 SE East Drive Bartlesville Mid High 4th hour 2-11-94 Abstract....................................................3 Introduction................................................5 Background..................................................6 Experiment..................................................8 Results.....................................................9 Conclusion.................................................11 Bibliography...............................................12 Abstract I did my experiment to find the effects of different shades of light on plants. Primarily I tried to find out which shades work best for photosynthesis and growth. I also wanted to find out which shades of the spectrum don't work well with plants. I hypothesized that white light would work the best because it contains all the colors of the spectrum. I also hypothesized that red would work the next best, followed by green and ultraviolet. The materials I used were four plastic drop lights, four 60 watt light bulbs, four large cardboard boxes, eight clear plastic cups, five inches of soil in each cup, eight pole bean seeds, a tablespoon measurer, and eight 1 cm diameter dowel rods. I planted each seed about 1 1/2 inches under the surface of the soil in each cup and made drainage holes in the bottoms of the cups. I installed the drop lights with a white bulb, red and green party bulbs, and an ultraviolet novelty bulb. I then put two plants and a light in each of the cardboard boxes. I then monitored each plant over a four week period of time, giving each 1 tablespoon of water every other day. When a plant first came above the soil, I put a dowel rod in for the plant to cling to. The results of my experiment were very interesting. The white light plants grew the best and looked the healthiest at approximately 11.5 and 10 inches. The plants under the red light grew to about 8 inches each, but didn't look as lush and strong as the white plants. The green light plants looked more healthy than the red plants but were only about 4 and 3.5 inches tall. The plants under the ultraviolet light had barely enough visible light to survive. They didn't even pop out of the soil until the third week, and grew only 0.6 and 1.4 inches tall. According to my experiment, plants grow best in white light. I believe this is true because the chlorophyll in the leaves can filter out which color of light works best2. Even though red light works very well with chlorophyll, white light contains other colors of the spectrum such as violet and blue which helps the plant greatly in photosynthesis3. Background Unlike many organisms, plants are autotrophic, meaning they make their own food. They produce their food through a process called photosynthesis. During this process, the plant takes in light energy, oxygen, and water to form the molecule glucose. A simple equation for photosynthesis is as follows: light energy 6O + H O C H O + 6O chlorophyll When light energy meets with chlorophll, electrons are excited which starts photosynthesis. The wavelength, or color, of the light depends on how much the chlorophyll will absorb. For instance, chlorophyll a (C H O N Mg) and chlorophyll b (C H O N Mg) absorb violet and red, but reflect green light. As a result, plants with chlorophyll a or b wouldn't grow well with green light. Since longer wave ultraviolet light is almost on the invisible side of the color spectrum, it probably wouldn't yield good results over a short period of time, either. White light, however, contains all of the colors of the spectrum. Therefore, plants can filter out which colors they need to use for photosynthesis from the white light. Since plants depend on the right colors of light for photosynthesis, and they must go through photosynthesis to eat, the color and quantity of light depends on how tall and healthy a plant will be. Since most complex life on earth is not autotrophic, we must obtain our food from those organisms who are. The only practical autotrophic food for us are green plants. Therefore, photosynthesis is the most important biological process on earth. Experiment For my experiment, I tested the effects of different colors of light on plant growth. The materials I used were four plastic drop lights, four 60 watt bulbs (different colors), four large cardboard boxes, eight clear plastic cups, five inches of soil in each cup, eight pole bean seeds, a tablespoon measurer, and eight 1 centimeter diameter dowel rods. First, I poked holes in the bottom of the cups for drainage. Next, I filled each of the cups 5 inches full of moist soil and planted one seed in each cup 1 1/2 inches under the surface of the soil. I then placed two cups each to a different light. Next, I put each of the pairs cups six inches apart from each other and twelve inches away from their light and covered the pairs and lights with the cardboard boxes. The colors of the light bulbs were white, red, green, and ultraviolet. After each plant grew about an inch out of the soil, I placed a dowel rod in the cup for support. I gave the plants one tablespoon of water every other day for a period of four weeks. I recorded the growth of the plants once a week with an inch ruler. Results Every week I recorded my data with a ruler as the plants grew. The plants under the white light grew the fastest. The first week both of the plants were about an inch tall. After the second week the plants were about two and a half inches tall. When the third week came around, the plants started going their separate ways; one measured 4.75 inches, while the other measured almost six. At the beginning of the fourth week, one plant was about 7.25 and the other measured slightly over 8.5 inches. At the end of the experiment the white light plants spurted to ten and 11.5 inches. At this point the plants had six opposing leaves. The pair in the red light, like the rest, stayed pretty much consistently the same size at their measurements. At the first week, the plants were just a little taller than the white plants at a little more than an inch. They grew about an inch each week for two weeks. At the fourth week, the plants were about five inches. By the last measuring, the plants grew three more inches. One plant had four large leaves. The other had two large leaves and a pair of mid sized leaves. These plants didn't look as healthy nd full as the white ones. This could have possibly been due to too many drainage holes. The plants under the green light didn't come up to the surface until the second week. By the third week, they were an inch tall, and at the fourth week, the plants were exactly two inches. At the end, the plants exhibited the same jump in size; one plant was 3 1/2 inches tall. The other was almost an even four. Both plants had but two small leaves and neither was really even big enough to wrap around the dowel rod, but they looked more healthy than the red plants. The plants exposed to ultraviolet light were overall a big disappointment. Neither even got to the surface of the soil until about halfway between the third and fourth week. At the end of the experiment, one plant was about a half an inch and the other was a little over an inch tall. These plants were much lighter in color than the others and only had two tiny leaves. Conclusions I am very pleased with the results of this experiment. Since pole beans grow relatively fast, I could get good results in a short amount of time. As you can see on the graph I made, the frequencies of the growth of the plants are very related. The only real flaw I had with this project was with the red plants' appearance, but as I have explained, this was probably due to some sort of drainage problem. Analyzing the graph, I can conclude with several facts. The first is that white light works the best to help plants grow and photosynthesize because it contains all the energy - rich colors of the rainbow. A second conclusion is that red light works fairly well because chlorophyll absorbs that color well. A third conclusion is that green light works poorly with plants because the chlorophyll in the leaves reflects it. A fourth conclusion is that long wave ultraviolet light is very bad in the exciting of chlorophyll because it is almost at the invisible end of the spectrum. A fifth and practical conclusion is that pole beans have a relatively large spurt in growth after the fourth week of planting. My final conclusion is that when trying to grow a plant, it is best to use sunlight.