Which Color of Light Best Effects the Growth of Radishes?

Researched by Katie W.


The purpose of this experiment was to determine the effect of different colored lights and the growth rate of radishes.

I became interested in this idea when my mother and I were planting a garden and we wanted to find out what we could do to increase the growth rate. 

The information gained from this experiment may help gardeners/farmers grow plants at a more rapid pace.


My hypothesis is that red light will increase the growth rate of radishes the most.

I base my hypothesis on a small but similar experiment my homeroom class did with, bean seeds. 

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The constants for all groups in this experiment were:

  • the amount of water a day, 
  • the size and type of pot, 
  • the temperature, 
  • the amount of light, 
  • the type of soil, 
  • the kind of radish seeds, 
  • how deep planted, 
  • how far apart planted,
The manipulated variable was the color of the light.

The responding variable was the growth of the radishes in centimeters from the tip of the root to the tiptop of the plant.

To measure the responding variable I used a meter stick with centimeter accuracy

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56.8 gm  Martinís Potting Soil
Regular Tap Water
Americaís Choice Radish seed packages
Planting Trays
1 Red roll Colored Cellophane
 1  Green roll Colored Cellophane
 1  Blue roll Colored Cellophane
 1  yellow roll Colored Cellophane
Clear Green House Covers
Water Trays

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1. Collect all materials
2. Put 56.8 gm of martinís potting soil in each  pot of 24.
3. Plant 2 radish seeds in each pot of soil about 5cm deep and about 5cm apart.
4. Place red colored cellophane over the clear greenhouse cover taping down sides so that     no unnatural light will pass through.
5. Repeat step 4 with yellow light.
6. Repeat step 4 with green  light
7. Repeat step 4 with blue light 
8. Label tray A (that will be under red light) with a small piece of paper on a toothpick labeled A.
9. Label tray B (with green light) with a small piece of paper on a toothpick labeled B 
10. Label tray C )that will be under blue light) with a small piece of paper on a toothpick labeled C.
11. Label tray D (that will be under yellow light) with a small piece of paper on a toothpick labeled D.
12. Label tray E that will be under regular light with a small piece of paper labeled E.
13. Place each colored greenhouse cover (with specific colored cellophane over it) over each tray.
14. Place the light  directly over the trays so each plant gets the same amount of light
15. Measure each day for 3 weeks.
16. After 3 weeks rinse the root from the plant and measure from the very lowest point of the plant to the very highest point of the plant.
17. Next you find the average (mean) of each plant under the different colored light.
18. Finally repeat steps 2-18 for experiment #2
19. Record all data and organize.

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The original purpose of this experiment was to figure out if the color of light would increase the growth rate of radishes.

The results of the experiment, as indicated in my table and graphs, are the lighter the color the healthier, stronger, and taller the plant.  The colors of light that had the most effect on the  growth of the radishes were the clear and the yellow light


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My hypothesis was that red light would increase the growth rate of radishes the most.

The results indicate that this hypothesis should be rejected. The lighter the color of the light the better the plant grows of this experiment. 

Because of the results of this experiment, I wonder if different radish seeds would change the out come.

If I were to conduct this project again I would use a different kind of seeds and see if the growth is as fast, I would also  use more of a variety of colors.

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Plants need several things in order to grow.  Nutrients (often from soil), water, and light are the essential elements.  Light provides the energy that plants must have. 


According to David Hershey in his book Plant Biology Science Projects, "Photosynthesis is a process by which green plants and other organisms produce simple carbohydrates from carbon dioxide and hydrogen, using energy that chlorophyll or other organic cellular pigments absorb from radiant sources." 
Photosynthesis occurs when chlorophyll from plants absorbs energy from light and uses it to help split apart water molecules to produce sugar and starch.
Photosynthesis normally is powered by the sun, but some green plants can grow indoors under an electric lamp or light.


To grow, plants need fertilizer in order to grow strong, healthy, and have strong roots. Most plants need water at least every other day (depending on the plant type and kind) 


Culture: Radishes grow best and taste better if they are grown under cooler temperatures so they can grow fast and constant.  Radishes need lots of water, because they donít do well in dry hot weather. 


Fertilizer contains plant hormones, vitamins and amino acids which are all things that a plant needs to grow strong, healthy and live a long time.

Plant Terms

Plant Agriculture: the study of how plants grow.
Plant Physiology: the study of how plants function.
Plant Ecology: The study of a plant relationship with other organisms and with its environment.

Fluorescent light

People sometimes use artificial light to grow many types of plants.   In this project the kind of light used was a fluorescent light so this information will help inform you more about fluorescent light.
According to the American Heritage Dictionary the definition of a Fluorescent Lamp is, a lamp that produces visible light by fluorescence, especially a glass tube coated on the inside with a fluorescent material and filled with amionized gas that emits ultraviolet rays.


Plants grow better when they are placed under some type of light.  Most plants are grown under the sun light outside but there can be exception for the sunlight. In this project the kind of light used was fluorescent light because of the weather conditions.  Not all plants can grow as good under unnatural light because of the kind of plant.  In this project the type of plants used were radishes, which responded to fluorescent light and indoor conditions.

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"Fluorescent Lamp" The American Heritage Student Dictionary.1994.  p. 392

Helms, Ronald N. "How a Fluorescent Lamp Works" The World Book Encyclopedia. 1995. Vol. F7 pp.305

Hershey, David R. Plant Biology Science Projects, 1995 p. 1-20




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