Does the color of light affect a plant’s growth? Is pink light the best color for plants to grow fast?
Dependent Measure: Height of the Plant
Independent Variable: Light Color
Hypothesis
I think light’s color affects plant growth, and ‘white’ light is the best for plants to grow fast.
Theory - Plants and Photosynthesis
Plants use the process of Photosynthesis to prepare food
Photosynthesis depends on the absorption of light by the pigments in their leaves (Chlorophyll-a, Chlorophyll-b, and Beta-Carotene)
The rate of absorption in plants changes with the wavelength of light
Only the Red and Blue ends of the light spectrum are used by most plants during photosynthesis
This is why the color of the leaf is green to our eyes (as it is reflected)
When plants are grown under artificial lights, red and blue colored lights are usually used to save electricity
Theory - Electromagnetic Spectrum
Visible light is a small part of the Electromagnetic Spectrum
Light travels through space as a wave, and the distance between two wave peaks is the wavelength of that beam of light
Wavelength determines the color of the light
A simple homemade spectroscope can help to view the spectrum of incident light
Procedure
Prepare materials and equipment
Cardboard boxes with dividers, 10 small plastic bags (air pillows cut in half), wheat grass seeds, soil and water
Equipment needed – Different color light sources (White, Infra Red, Ultra Violet-A, Red, Blue, Green), Electronic circuit for controlling the brightness of the light sources, Cell phone charger, Mains timer, and tape measure
Initial experiment setup
Fill 10 plastic bags with adequate soil and plant 5 wheat grass seeds each and water them
Place each bag with soil and seeds in one of the divided areas of the cardboard box and make sure that no external light can enter the box
Make holes for the light sources at the top of the box for each of the divided areas and install the lights
Connect the cell phone charger to the timer and set the timer to be ‘ON’ for 12 hours a day
Monitor the box daily to see whether the seeds germinate and water them if needed
When plants start to germinate, record the height of the plants under each light color using the tape measure in centimeters
Continue to record the height of the plants daily for 10 days and water them if needed
Experimental Setup
Results
Comparison
Observations
Plants grown under infrared light or darkness were yellow and looked more like sprouts than plants, they did not have any leaves
Plants grown under white, blue, and ultraviolet light had lush green leaves and could support their weight on their own
Light sources used in the experiment were not monochromatic as other colors can be seen under the spectroscope
Conclusions
My hypothesis that white light is the best for plants to grow is correct.
Plants can also grow well in Blue, Red, and Red+Blue color lights
LED is not an ideal monochromatic light source as I could observe the presence of other colors using the spectroscope.
If only an artificial light source is available, we could use a combination of Red and Blue colors instead of white light to save electrical power.
References
Books
Young Scientist – Living World & Plants – World Books
The Green Kingdom – Childcraft
Help Your Kids with Science – Dorling Kindersley
Young Scientist – Light & Electricity – World Books
Practical Electronics for Inventors – Paul Scherz & Simon Monk
Online Resources
Light Absorption for Photosynthesis - hyperphysics.phy-astr.gsu.edu/hbase/Biology/ligabs.html
