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The Affect Differentiating pH Levels and Visible Light
Spectrums have on the Rudbeckia Hirta
Xxxxxx Xxxxx
Marine Academy of Technology and Environmental Science
Research Proposal
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Introduction:
All plants absorb and require different wavelengths from varying color spectrums. Each color
plays a different role in the plant’s health and growth. In particular, plants utilize wavelengths
between 400 and 700 nanometers (nm) (refer to Figure 2 on page 6) in order to carry out
photosynthesis. In my research, I shall be focusing on the major visible light spectrums: red,
orange, yellow, green, blue and violet/purple. Red wavelengths, which are longer than the others,
the most important wavelengths ranging from 640 to 680 nm, aid in, “…stem growth, flowering
and fruit production, and chlorophyll production. The red wavelengths are known as warm light
and they are naturally more prevalent in sunlight during the shorter days of fall and winter,”
(Watkins, Diane). Plants give off a green color because the green and yellow that reaches the
plant are reflected, although some of these colors’ wavelengths are taken in to complete
photosynthesis. Blue wavelengths from the spectrum known as cool light, most importantly
ranging from 430 to 450 nm, “…encourage vegetative growth through strong root growth and
intense photosynthesis. Blue light is often used alone during the early phases of plant growth,
such as starting seedlings, when flowering is not desired,” (Watkins, Diane).
Light duration is an especially important factor in plant growth. Specifically, plants grown
indoor, beneath simulated lights, need at least 12 to 14 hours of light per day. Darkness is
essential to permit the plant to rest and generate the blossoming response (Watkins, Diane).
Plants which bloom in different seasons call for different time periods of light availability and
darkness. Short day plants demand short periods of light and long periods of darkness. Long
day plants demand long periods of light and short periods of darkness. There are also day neutral
plants that can do well in changing conditions.
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One other crucial factor towards plant growth is soil pH levels which measures the fertility of
soil. The levels of pH help to indicate the acidity of the water within the soil and what chemicals
are needed to purify it. It is important to know a soil’s pH in order to diagnose, “… nutritional
problems of agricultural crops and other plants,” (D.E. Kissel and P.F. Vendrell, September
2004).
The pH in plant soil can be altered to sustain a balanced concentration, “Most garden soils have a
pH between 5.5 and 8.0. If the pH level is below 6, the soil is too acidic, and you need to add
ground limestone. If the measurement is above 7.5, the soil is too alkaline for most vegetables,
and you need to add soil sulfur,” (Nardozzi, Charlie and Nation Gardening Association).
During this study, I will analyze the affects that occur when a single kind of flowering plant, the
Rudbeckia hirta, is secluded to only one kind of color from the light spectrum with four different
varying pH levels from four to eight (refer to Figure 2 on page 6). The plant selected for use will
be a model kind of vegetation for experimental purposes.
The Rudbeckia hirta, commonly known as the Black-eyed Susan, is usually grown with soil pH
levels that neutral, and, “…when the soil temperature has reached 70 degrees F for best seed
germination… [germination] takes 7 to 30 days,”(The Old Famers Almanac, September 10,
2015)
Hypothesis
By measuring the growth of the plants using pH levels and selected visible color spectrums, I
will find the optimum conditions for plant growth. Due to the fact that wavelengths in the red
and blue ranges are the most abundantly absorbed, the plants receiving these two spectrum colors
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along with having a pH level of seven will grow the most, being provided with the finest
growing environment.
Methodology
1. Plant Quantity and Usage
A. 120 plants of the same kind will be planted
B. 20 plants will go under each different light spectrum being used
i. red, orange, yellow, green, blue and violet/purple
2. pH Levels
A. Under each light, the twenty plants will be split up into four groups of five
each measuring at a different pH level
i. levels four through eight
B. pH will be checked three times a week in order to maintain steady levels
i. any materials will be added to maintain soil pH
3. Growth measurement will be taken and compared once a week
Site
All plants will be grown in a basement which will be kept at a fixed temperature and will provide
assurance that the plants will not be exposed to any other light then that of the colored and
artificial bulbs.
Estimated Timeline
October

Purchase of material
November
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Set up of materials

Begin Experiment
December - February

Keep track of all data being collected in an organized manner
March – April
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Bring experiment to a close
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Analyze collected data to come to a conclusion
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Create visual representation of data and work on oral presentation
References:
"Black Eyed Susan Flower: Tips For Growing Black Eyed Susans."Gardening Know How. 30
June 2011. Web. 19 Oct. 2015.
In this website certain plant preferences are addressed along with ways to maintain its
health.
"Black-eyed Susans." The Old Farmer's Almanac. 25 Feb. 2010. Web. 19 Oct. 2015.
Common facts about the Black Eye Susan were featured on the website along with
instructions on how to plant the seeds properly.
Does The Color of Light Affect Plant Growth? (2006). Retrieved October 14, 2015.
This website gives instruction on how to construct such an experiment with colored
cellophane, although according to other sites colored light bulbs would be more effective.
Dr. John Ott: The Light Side of Health. (n.d.). Retrieved October 14, 2015.
This website focuses on John Ott’s research and actions he took in his career as a
botanist. He was one of the first people to begin studying how the different light spectrum affects
the gender of incomplete flowering plants.
Nardozzi, C. (n.d.). How to Adjust Soil pH for Your Garden (National Gardening Association,
Ed.). Retrieved October 15, 2015.
Information on how to maintain pH levels in soil is provided in a noncomplex way.
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Plant Growth & Light Color. (n.d.). Retrieved October 14, 2015.
This website gives additional information on how to conduct such an experiment and
what results you may be looking for.
Soil Testing:. (n.d.). Retrieved October 14, 2015.
This website provides information on the importance of pH levels in plant fertilizers.
The Best Plant Light Spectrum for Growing Flowering Plants. (n.d.). Retrieved October 14,
2015.
This website focuses on the exact measurement of wavelengths plants prefer and the most
important wavelengths with each color on scale of the color spectrum.
UCSB Science Line. (2015). Retrieved October 14, 2015.
This website gives information about the wavelengths of colors in which plants absorb
during different stages of growth.
"UV-Visible Spectroscopy." UV-Visible Spectroscopy. 5 May 2013. Web. 15 Oct. 2015.
This website provides the information from Figure 1 about visible spectrums and their
measurements in nanometers.
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Violet: 400 - 420 nm
Indigo: 420 - 440 nm
Blue: 440 - 490 nm
Green: 490 - 570 nm
Yellow: 570 - 585 nm
Orange: 585 - 620 nm
Red: 620 - 780 nm
Figure 1: The image provides the visible spectrums ordered from shortest to longest
wavelengths along with a corresponding key of measurements to the right.
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Figure 2. Image of pH levels on a scale being compared to everyday liquids.