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Plants and Color Light

What Color Light Is best for Plant's Growth?

Introduction: (Initial Observation)

Sunlight contains different color lights. When a rainbow or a prism break the sun light to it’s components, we can then see all different colors of the light. White light like sunlight contains all different color lights. Plants need light to grow, but which of these lights are the most effective for plants growth? This question can be the subject of a research project. This research may show that a certain color light may cause faster growth and increase flowering/budding in plants

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 light as a source of energy for plants. Read books, magazines or ask professionals who might know in order to learn about the effect of light on plant growth. Keep track of where you got your information from.

Refer to the following web sites to gather more information. You may also find books about growing plants with synthetic light in your local library.



If you search the Internet, search for light energy and photochemical energy.

Photons have an energy which is dependent upon the wavelength of the light. The rule is:

Long wavelength light = low energy

Short wavelength light = high energy

When an opera diva shatters a glass with her singing voice, the glass absorbs resonant sound energy. To be “resonant” the frequency (or wavelength or energy) of the sound must exactly match that of the glass. And so it is with electromagnetic radiation and chemical species.


Valuable Concepts

Chlorophyll (a & b) – plant pigments

Carotene– a plant pigment

Xanthophyll– a plant pigment

Phycobilin– a plant pigment

Chromatography – a process used to separate and optionally to identify compounds based on their solubility

Transmittance – a measure of the amount of light passing through a solid or fluid

Absorbance – a measure of the amount of light absorbed by a solid or fluid

Wavelength – a measure of light referring to the distance from one peak of a light wave to the next

Visible Light Spectrum – portion of the electromagnetic spectrum that we can see

Absorption Spectrum – the spectrum of light that a particular solid or liquid absorbs

Action Spectrum – the range of light that results in a particular activity

Solvent/Solute – the liquid portion of a solution and the substance dissolved 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 “What color light is best for plant’s 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.

The Independent variable is the color of the light (white, blue, green, red).

The dependent variable is plant growth (increase in plant height).

Controlled variables are temperature, water and air. (We make sure that all sample plants are growing at the same temperature and with the same amount water and air.


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.

This is a sample hypothesis:

I think the red color is the best for plant because it is the color of heat.

This is another sample hypothesis:

I think the blue color light is the best for plant because it has a higher frequency and higher energy.

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.”

We plant some seeds and observe their growth under different lights. In our design we have decided to grow seeds in film canisters, but you can also use ceramic pots or even plastic cups for this purpose.

Film Canister Preparation:

  1. Using a 5/63″ drill bit, drill 3 holes in bottom of each film canister, as close to edge as possible. Do not drill in the center, raised portion of the canister.
  2. Allow canisters to air dry on a piece of paper towel.

Ruler Construction:

  1. Using a metric ruler and a sheet of white paper, create your own ruler, about 18 cm high and 1 cm wide. Mark millimeter increments on the ruler, starting from zero at the bottom.
  2. Make 20 photocopies of this ruler, and cut to size. You should have 20 paper rulers (18 cm x 1 cm) with mm increments.
  3. Cut 20 rods approximately 21 cm from the straight edge of a wire coat hanger. Using small pieces of scotch tape, tape each paper ruler to it’s own rod, placing the bottom of the ruler about 3.5 cm up on the rod.
    You may also be able to use cardboards to mount your ruler, but don’t make it wide because it may reduce the amount of light that gets to the plant.

How to make color light?

You can create color light for your experiment in two different ways. One way is using color light bulbs.

You can purchase color light bulbs in blue, red, green and yellow colors. We have used 100 Watt Colortone Outdoor Flood bulb by Phillips that creates enough light for plants. These lights will get hot, so they should be mounted in a safe socket. If you use these type of light bulb, keep them at least 2 feet above the plant. Also remember to turn off the lights every night to simulate normal light cycle.

The method that I prefer is filtering the natural day light to get a specific color. We can do that by using color cellophane. You can purchase color cellophane from art stores, gift stores or your local flower shop may have some. Somehow make a cube structure and cover it with the cellophane.

To make the cube you can use balsa wood. Balsa wood can be purchased from craft stores and hobby stores. But if you did not have access to balas wood, use any wire or plastic rod. It will do the same. In this experiment I used a utility knife to cut some sturdy board strips and I used them co construct a cube.

Balsa wood and sturdy board and foam board, they can all be glued using Elmer glue or any other paper glue or wood glue. You may also use pins to hold them together while its being dried.

When your cube is ready, you can simply put a sheet of cellophane over that. You may also decide to do a better job by cutting the cellophane and gluing it to the rods. This will complete your color light box.

I got some small ceramic pots to plant the seeds. These pots do not need a hole at the bottom, because extra water can easily exit from the walls of the pot.

Planting Seeds:

  1. Half fill each canister with potting soil. Moisten soil with 1 ml water from a pipette (1 ml is 20 drops if you want to use a dropper instead).
  2. Drop 4 fertilizer pellets into each canister.
  3. Continue filling each canister with soil.
  4. Make 4 shallow depressions on surface of soil equally spaced from canister edges and each other to keep as much distance as possible between plants.
  5. Drop one seed into each depression for a total of 4 seeds in each canister.
  6. Sprinkle soil over seeds till they are just covered.
  7. Gently dispense 4 ml water into each canister, 1mL at a time.
  8. Place one constructed ruler into the back of each canister so that the 0 cm point is aligned with the top of the soil. These rulers should remain in place until end of the experiment.
  9. Place prepared canisters into color light boxes, 5 canisters in a row in each box.
  10. Attach a different color filter (Cellophane) to each of the boxes, leaving enough space for the plants to mature.

Choosing a spot for the experiment (when you use light bulbs):
If you use light bulbs, hang or attach lights in a row, so that one plant box can be placed under each light. If possible, isolate the experiment from external light sources by shielding the entire apparatus (lights and boxes) with cardboard “walls” and a back wall, or by using drapes. Shielding materials should be made of white or light colors to reflect light back on to the plants. A drape provides for easy access to plants for everyday observation, yet should only be used with low wattage fluorescents, as it can be a fire hazard with hot bulbs.

If you decide to use fluorescent bulbs, the containers must be placed as close to the lights as possible to attain optimum growth for the plants (5-8 cm from top of plants, but no more than 25 cm). Also it is not easy to find color fluorescent bulbs, so you may need to use color cellophane to filter their color. To do this, you may wrap the fluorescent bulb with cellophane or just use your cubes covered by cellophane.


  1. The soil in each canister must be kept moist at all times. On the other hand, it should not be “soggy.” Watering each container everyday with 1-2 ml of water should be sufficient to keep the soil from drying over night. If several days must pass without any attention to the plants, use a little extra water (3-4 ml), and any excess water will be absorbed by the filter paper below the canisters.
  2. Observe of height, color, growth, and bud/flower growth daily at time of watering. Both watering and observation should occur at about the same time of the day, each day, throughout the experiment. The day on which the seeds are planted is Day 0.


  1. Record your observations of plant growth in a daily log. Include information on the color of the filter, plant height, number and size of leaves, formation and development of flowers, etc.
  2. Create a data table for each plant, including the following information: Color of filter, time (days), plant height (cm).
  3. Graph plant height vs. time for a representative plant from each container.

You may compile your data in different forms. One results table may look like this:

Plant growth rate under different color lights

Color of light Plant height after X days Plant weight after X days
Natural (control)

X is the number of days from planting seeds to the end of experiment and measurements.

Materials and Equipment:

    • Brassica rapa “Fast Plants” (200 seed packet)
    • specially formulated potting soil
    • specially formulated slow-release fertilizer pellets
    • Small boxes (If you want to use color light bulbs)
    • Color Filters (Purple, Blue, Yellow, Green, Red cellophane)
    • (20) black film canisters or similar container (caps not needed)
    • (20) wire coat hangers
    • 4 color light bulbs
    • (2) 18″ Fluorescent grow bulbs with fixtures
    • several pieces of cardboard or foam core
    • filter paper
    • spatula (or small spoon)
    • balsa wood (48 small rods, about 1 foot each. )
    • 5′ 18 gauge copper wire
    • plain white paper
    • drill with 5/64th, 7/64th, 9/64th drill bits
    • water
    • 1 ml plastic disposable pipettes

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.


    1. Compare the plant growth for each of the light filters, describing the effects of each color filter.
    2. Based on what you know about photosynthesis and energy transfer, explain why some filters affected plant growth more than others.
    3. Choose two filter colors, and predict the affect of shielding plants with both filters.
    4. Design an experiment that would test what type of indoor lighting would best promote plant growth. Predict the results of the experiment, providing a rationale based on what you have learned from this experiment.

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 related to plant growth and photosynthesis. Use such books as your references.

Why do plants grow better under certain light conditions than others?


Introduction to photosynthesis

Photosynthesis and the web

Photosynthesis Rate

What color light helps plants grow? (ABSTRACT)