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What Is The Effect Of Light In Plant’s Growth?

What Is The Effect Of Light In Plant's Growth?Light or Gravity?

Introduction: (Initial Observation)

Plants are the main source of food and nutrients for human and animals. Many plants are grown as food products. We use the fruits, leaves, seeds or roots of such plants as foods. Some other plants are decorative plants and are grown for their colorful and beautiful leaves and flowers. Can you think of other reasons that plants may be grown? How about medical use, exotic fragrance or insect repelling properties?

No matter why you grow plants, you want them to grow as fast as possible. If you are in business of growing plants, faster plant growth results in a higher income for you. In order to be able to speed up plant growth, you need to know how different factors may affect plant growth. Light is one such factor that can be studied. In this project you will study to find out “What is the effect of light on plant growth?”.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about plants and factors affecting plant growth. Read books, magazines or ask professionals who might know in order to learn about the effect of different factors on plant growth. Find out what happens if plants can not access water and nutrients. Keep track of where you got your information from.
Following are samples of information that you may find.

Many modern farmers grow plants in warehouses, buildings, basements or other closed areas.

PHOTO: Darren Foster
Stewart Borowsky, urban farmer, with his wheat grass in a grow room of the warehouse farm in Brooklyn, N.Y. Source…

6 Tray Sprouter

This sprouter will fit into almost any living space and it provides enough wheat grass for 3-4 ounces of juice per day, usually more, depending on your microclimate. It holds six 10 x 20 trays of wheat grass.

HYDROPONIC or SOIL – I recommend growing in a sterile material used widely in hydroponic gardening. There is less chance for mold to develop and less mess. Tray grown wheatgrass roots do not take up nourishment from the soil, they are too young. All the nourishment comes from the miracle of the seed itself and the seaweed fertilizer that is included with the sprouter and is added to the water. You get all the minerals on the planet in a perfect ratio with this kelp product and it is easily absorbed by green leaves and roots.

I am concerned about all the animal wastes in potting soils, however, if you have a fervent belief that growing in soil is better, then you certainly can do so in this sprouter. It is your choice and you can test both mediums for yourself. You may find that mixing the hydroponic medium with peat moss is the best solution. Peat moss is the basic material that Ann Wigmore used and has no animal wastes in it.


Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to find out how does light affect plant growth?

Three identical plants will be grown in identical conditions but different amounts of light in order to see the effect of light on plant growth.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variable (also known as manipulated variable) is light. Possible values being tested are no light, low light and high light.

Dependent variable (also known as responding variable) is plant growth. A good representation for plant growth is plant height.

Controlled variables are water, temperature and nutrients.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are two sample hypothesis.
1. Light will have no affect on plant growth. My hypothesis is based on my observation of some healthy plants in low light places.

This second sample hypothesis is exactly opposite of the first one.

2. Light is the main source of energy for plant and plants can not grow without light. My hypothesis is based on my observation of plants growing around my house. Plants in constant shade do not grow well while plants in sunny spots grow fast.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Introduction: In this experiment you will grow wheat grains or lentil in three identical plates and place them in different amounts of light. Make daily observations and record their growth rate. In the following procedure we use the term seed to represent wheat grains or lentil seeds that you may choose to grow.


  1. Put some seeds (about 500 grams or 1 pound) in a bowl and add water until the seeds are covered with about 5 cm of water. Cover the bowl to keep bacteria away and leave it for 1 day.
  2. Remove the soaked seeds and wrap them in a wet towel. Keep the towel wet or moist for 2 to 3 days until the seeds germinate. Wet towel provides moisture required during seed germination. When the seeds germinate you will see small white roots and stems exiting the seeds.
  3. Remove germinated seeds and place them in 3 identical deep trays or dishes. Make sure you put same amount of seeds in each dish. Try to have at least a layer of 1 inch or 3 centimeters of seeds in each plate. Add about 1 centimeter water at the bottom of each plate. Cover all three plates with wet cloth to hold the moisture. Continue your daily observations and make sure that the cloth remains moist. Spray some water on the cloth if needed. You may also spray the seeds to keep them moist if you feel that they are dry. Seeds will remain in this condition for 2 days.
  4. Remove the cloths covering the seedlings and label the dishes as “Dark”, “Low-Light” and “High-light”.
    Place all three plates side by side about 2 feet apart on a table. In this way all three samples will be in the same room temperature. This is where your experiment and data recording starts.
  5. Cover the plate labeled dark with a carton box or some aluminum foil so it will not get light. Put a desk lamp right above the plate labeled “High-light”. You may use a paper or cardboard to make sure that the light from desk lamp does not get to the other plates. If your desk lamp has a fluorescent bulb, you are fine; however, if it has a regular light bulb, remove it and replace it with a compact fluorescent light bulb. The heat produced by regular light bulbs may cause a problem. (Remember that temperature is one of your controls. So you must make sure that all three samples are growing at the same temperature).
  6. Make daily observations and water the plants (about 1 cm at the bottom of each dish). Measure and record the average height of each plant dish every day. Record your results in a table like this:
Days after removing the cloth and starting light variations. Height of plant in Dark Height of plant in
low light/ room light
Height of plant in
High Light

Questions and answers:

How does the sprout look like?
The shape of sprouts or germinated seeds depend on the the type of seed that you choose to grow. In general seeds may partially open and a white root and a white stem extend out from each seed.

What type of wheat should I use?

The wheat grains that you use must not be broken. You may use cleaned wheat that consists of the kernel only. You may also use un-cleaned wheat that is the whole seed including “glumes,” or husks and the kernel inside them.

What happens if I don’t add enough water?

In most cases, excess amount of water is more harmful than shortage of water. In general all plants need access to water and moisture. A small amount of water at the bottom of the plate is enough. Roots reach to the bottom and get the water they need.

How far should the light be from the plant?

Put the light about 1 foot or 30 centimeters above the plant. As plant grows, you may need to rise the light as well.

Materials and Equipment:

A sample list of material is as follows:

  1. 750 grams wheat or lentil
  2. One spray bottle
  3. One towel
  4. three pieces of cotton cloth
  5. 3 deep ceramic or glass trays
  6. Desk lamp with fluorescent light or compact fluorescent light.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Your main results are in your results table; however you may include your daily notes in your results as well. Observations such as color of plants, their general appearance, their disease or dying plants may be reported as well.


No calculation is required.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


Visit your local library and find books about plants, seeds and botany. Following are some web references. You can search the Internet for more related material.