Does Colored Light Affect The Growth Rate Of String Beans?

Researched by Allison E.


The purpose of this experiment was to find out what colored light bulb would increase the growth rate of string bean plants the most after eighteen days of growing under a colored light bulb. 
I became interested in this idea when I was looking for an idea for a project and I came across this one more that once.  Then I thought it would be an interesting experiment to conduct.
The information gained by this experiment will benefit society by, if farmers that grow beans indoors want to speed up the growth rate, they can see which color of light bulb will make beans grow the fastest.


My hypothesis is that the red light bulb will increase the growth rate of string bean plants more that the clear, blue, and yellow light bulbs will.
I base my hypothesis on the fact that, "When used alone, red light will make plants grow tall and spindly," stated in an article on the internet called "House Plants-Artificial light."

Experiment Design

The constants in this study were:

  • The type of bean seed
  • Amount of soil in each cup
  • Amount of water that each plant gets
  • The amount of light that each plant is exposed to 
  • The temperature of the plants surroundings
  • The depth in witch each seed is planted
  • Same size and width of the cups
The manipulative variable was the color of light that each plant was exposed to.  The four groups of six will each receive a different color of light.  Group A will be exposed to a red light bulb, and group B will be exposed to a blue colored light bulb.  The group C will receive a yellow light while D receives the light from a plain light bulb.
The responding variable is the height of the string bean plants after 18 days of growing.  To measure the growth of the string beans you would take a ruler and set it on the soil and measure to the highest point of the plant and record the height.

24 string bean seeds
4  colored light bulbs (red, yellow, blue and clear)
1 grow box
4 trays or tubs to set plants in
24 250 ml Styrofoam cups
1 ruler
1 measuring cup
1  poking pencil
30 pieces of tape for labeling
4680ml  purified water
3900ml  seed starting potting soil


1. Gather materials and carefully poke three holes in the bottom of each of the 26 cups with a pencil for water drainage.
2. Use the measuring cup and put 100ml of seed starting potting soil in each Styrofoam cup.
3. Then place a string bean seed in the center of each cup and fill the cup with 50 more ml of soil.
4. After that, sprinkle 5ml of purified water in each cup and divide the 26 cups into four groups of six.
5. Set each group of cups into different water trays and label the cups A1, A2, B1, B2 and so on, then label the trays A-red, B-blue, C-yellow, and D-clear.
6. Put a sheet of plastic wrap over each tray and place in the compartment of the grow box that bulb matches the label (donít turn the light on).
7. Let the trays sit in the grow box with the cover down until the plants start to germinate and you can see the seeds sprouting.
8. Then you turn the light on at 7:00 in the morning and turn it off at 10:00 at night every day for 18 days.
9.  But at 3:00 each day you need to measure each plant by setting the ruler vertically at the base of the soil and measure to the highest point of the plant.
10. Then record your data.  Measure each plant everyday at around the same time.
11. Also, everyday you need to sprinkle 5ml of purified water on each plant.
12. At the end of the eighteen days you can throw the plants away and clean out the grow box and the materials.
13. To find the average growth of the plants you would add together the highest height of all the plants in one group and divide by six to find the average growth.
14. Find the average to all groups and find out which color of light bulb works the best.


The original purpose of this experiment was to determine which colored light bulb would increase the growth rate of string beans the most after eighteen days of growing. 
  The results of this experiment were that the plants growing under the clear light bulb grew the highest out of the plants under the red, blue and yellow light bulb.  The average growth for the clear light bulb was 32cm, the yellow came in second with 28cm and the red got third place with an average of 23cm.  The plants under the blue colored light bulb grew the least; the average for the blue was 17cm.  Therefore, the best light bulb to use is the clear light bulb.

See my table and graph.


My hypothesis was that was that the red light bulb will increase the growth rate of string bean plants more than the blue, yellow, and clear light bulb will.  The results indicate that my hypothesis should be rejected.  The plants growing under the clear light bulb grew the highest, not the ones under the red.
Because of the results of this experiment, I wonder if the clear light bulb made the plants grows the highest because it is the color closeted to natural sunlight.  My findings should be useful to farmers who plant beans indoors, because they now know to use a clear light bulb.  If I were to conduct this experiment again, I would use more colors of light bulbs and more bean plants.
Research Report 


 Have you ever wondered if you could grow string beans under a different light source rather than the sun?  Like maybe a plane incantation light bulb or a colored incantation bulb?  Well I did, so I decided to do a science project on it and write a research report.  I found out about the wavelengths of colored light and about artificial light.  A topic that interested me was about the history of string bean plants.  I also learned about photosynthesis and germination.  Another topic that I researched was about plant cells.  I then put all of my research together into one big research report. 


 I painted the "grow box" the color white so that the light would reflect off of the white walls and go back into the plant.  Reflection is a line that is like a ray of light.  Reflection is when light rays bounce off the walls, like in my box, it is all painted white so the light rays bounce off of the walls and keep doing so until it hits something that will absorb it, like a plant.  An example of reflection are that when you look into a mirror or a body of water when the sun is shining or the light is on, the light rays bounce off of the mirror or water into your eyes so you see your reflection.  Reflection is a very useful tool in growing plants indorse for more light. 

Plant Cells

 A plant, like string beans, is made up of thousands of tiny little microscopic plant cells.  A plant cell consists of eleven different major parts.  They are; cell wall, cell membrane, Golgi body, nuclear membrane, nucleus, ribosome, cataclysmic residuum, cytoplasm, mitochondrion, vacuole, and chloroplast.  The nucleus is the control center for the whole cell, most cells have a nucleus.  Outside of the nucleus there is the nuclear membrane.  A nuclear membrane is very thin, cells have one so it can block of the rest of the cell from the nucleus.  A cell wall is kind of like the nuclear membrane but it is stiff and it supports the cell.  It is like the nuclear membrane because, they both are walls that surround and protect something.  A cell membrane is made up of proteins and lipids; it surrounds the cytoplasm and nucleus.  Cytoplasm is a goo substance that all of the livings materials are made of accept the nucleus.  The rest of the plant cells are made up of organelles.  The organelle that creates and transfers materials to one place to another is called a golgi body.  An endoplasmic reticule is an organelle that does almost the same thing as the Golgi bodi.  It transfers materials from one place to another.  Another organelle is called ribosome; it makes and gives protein to the cell.  Chloroplast is an organelle that all it does is hold chlorophyll inside the cell.  The last two organelles inside a cell are vacuole and mitochondrion.  Vacuole stores food, water, and wastes, it also disposes of the wastes that it stores.  Mitochondrion is like the powerhouse of the whole cell it provides it with all of its energy.  All of those things are what makes up a plant cell. 

String Beans

String beans are probably one of the most popular vegetables throughout the world, but there are some things that you need to know if you are going to grow them.  People first found out that you can eat string beans and they actually tastes good, when a long time ago a cook was making a soup and one of the beans from his plant fell into the soup, before he realized that it was their he had already served it and the people noticed how good they were.  String beans are quite healthy; 250ml of string beans have about 30 calories.  They have lots of calcium, potassium, phosphorous, and tons of vitamin A.  There are many diseases that string beans can get, but thankfully there are easy ways to tell if your beans have them.  Some diseases are; anthracnose blights, damping off, and rot.  To tell if your bean has anthracnose it will ooze a pinkish liquid.  Blights, you can tell if there are watery spots on parts of the plants foliage, and damping off, the bottom of the stem will become very mushy (this is common in starting seeds).  If you shake or perhaps drop a bag of seeds, it can damage them and cause your plants to mature slower or not at all.  Remember all of these things when planting string beans, and donít forget that they are yummy and healthy for you.

Colored Light and Wavelength

 Colored light and wavelengths are an important part of my project, and the facts about them are very useful to know.  The different dencity in the different colors causes different colored lights to have different wavelengths.  The colors that wavelengths are four hundred nanometers are the lighter and more dense colors like violet, indigo, and blue.  Then there is the colors that are a little bright like green and yellow, those are five hundred nanometers.  The colored lights that are six hundred nanometers are more bright colors like orange and red.  Colors that donít have a high wavelength have a high level of energy to grow.


  • Science Insights/Wesley Addison/Plant Cells



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