Light from the Sun is a full spectrum of different wavelengths of light. Scientists refer to this light as “white light”. When the wavelength of visible light changes, so does the color seen by the eye. The shortest wavelengths visible to the human eye are violet (400 nanometers). The longest wavelengths visible the human eye are red (700 nanometers). Each plant is affected differently by the changing wavelengths of light. The purpose of this experiment is to test the effects of different wavelengths on raphanus sativus (radish). The hypothesis is that wavelengths below 450 nanometers will increase raphanus sativus growth and wavelengths above 650 nanometers will decrease raphanus sativus growth. However, the data slightly supported that both wavelengths below 450 and wavelengths above 650 slightly increase raphanus sativus growth.
Introduction/Background: Plants use light to turn carbon dioxide into sugars necessary for growth, a process called photosynthesis. Sunlight is a full spectrum of different wave lengths of light. Seen through a prism, this spectrum turns into bands of color: red, orange, yellow, green, blue, indigo and violet.1 However, changing the wavelength of light may shorten this process even more.2 Many of the results from other experiments have shown that this differs from plant to plant.3 In a previous experiment, done by Hamaker K., results have shown that vines under green light have shown more growth than vines under “white light”.4 However, an experiment done by Morton J. L., lima beans actually grow the best in “white light” and the poorest in green light.5 The conclusion is that different wavelengths of light in the visible spectrum have varying effects on the growth of photosynthetic plants.6 The purpose of this experiment is to see if different wavelengths of light affect the growth of raphanus sativus.
Methods: The materials needed for this experiment are 3 cardboard boxes (3ft x 3ft x 3ft), Topsoil, a red light bulb (60 watts), a violet light bulb (60 watts), a white light bulb (60 watts), and radish seeds. First, the scientist will put 5 inches of topsoil in each cardboard box. Second, the scientist will plant the radish seeds half an inch below the ground and half an inch apart. Third, the scientist will place each box under a different colored light bulb. Fourth, the scientist will add a cup of water to each box daily. Fifth, after 28 days the scientist will unplow the radishes and analyze their growth.
|White Light (cm) |5.9 |
|Red Light (cm) |10.99 |
|Violet Light (cm) |10.29 |
Results: The independent variable was the color of the light bulb and the dependent variable was the growth of the raphanus sativus. The average for the white light was 9.47 cm, red light was 10.99 cm, and violet light was 10.29 cm. The white light’s range was 7.4 cm and standard deviation was 2.43 cm. The red light’s range was 4.1 cm and standard deviation was 1.31 cm. The violet light’s range was 6.7 cm and standard deviation was 2.18 cm. The P-value from the Red vs White 2 sample T-test was 0.051721012717. The 2 sample T-test for Red vs White didn’t support the hypothesis. The P-value from the Violet vs White 2 sample T-test was 0.218568351982. The 2 sample T-test for Violet vs White slightly supported the hypothesis.
Conclusion: This project has proved that red light and violet light both slightly increase the growth of raphanus sativus. But, the P-values in the 2 Sample T-tests showed that the only part of the hypothesis was supported. The data shows that wavelengths of light above 650 and wavelengths of light below 450 increase radish growth. However, some sources of experimental error in the project might have been that the boxes did not receive equal amounts of water or some seeds were healthier than others. Some limitations of experimental design were that raphanus sativus naturally grows outside and experts say that it is not recommended to grow it inside. However, a question for further study is: do different plants have the same effects to different wavelengths of light as raphanus sativus?
1. Quinn I. Strauser. The Effect of Different Colored Light on Plant Growth. CALIFORNIA STATE SCIENCE FAIR. 2007. [Accessed 2012, September 18] Available at: http://www.usc.edu/CSSF/History/2007/Projects/J1730.pdf 2. Adam Z. Kalawi. Does the Color of Light Affect Plant Growth?. CALIFORNIA STATE SCIENCE FAIR. 2005. [Accessed 2012, September 21] Available at: http://www.usc.edu/CSSF/History/2005/Projects/J1625.pdf 3. Kiri Hamker and Suomalainen Yhteiskoulu. The Effect of Different Colors of Light on the Growth of Young Specimens of the Helianthus Annus (Sunflower). 2003. [Accessed 2012, September 21] Available at: http://www.aka.fi/Tiedostot/Tiedostot/Viksu/Viksu2003/Kiri%20Hamakerin%20ty%C3%B6.pdf 4. N/A. Photosynthetic Pigments. University of California. 2007. [Accessed 2012, September 21] Available at: http://www.ucmp.berkeley.edu/glossary/gloss3/pigments.html 5. Richard Hoyt. How Does Color of Light Affect Plant Growth? Garden Guides. 2004. [Accessed 2012, September 24] Available at: http://www.gardenguides.com/87235-color-light-affect-plant-growth.html 6. N/A. Does the Color of Light Affect Plant Growth?. Fulvic Acid. 2010. [Accessed 2012, September 24] Available at: http://www.fulvicacid.homehydroponics.info/plant-growth/does-the-color-of-light-affect-plant-growth
Acknowledgements: I would like to thank my teacher Mr. Whittaker for helping create the idea of this project. I would also like to thank my father Omar Khatib for helping me obtain the materials necessary for this project.