Comparing types of artificial light on plant growth

Introduction: (Initial Observation)

Sunlight is the perfect source of energy for plants; however, sunlight is not available all the times and in all places. For growing plants indoor, we need to substitute sunlight with artificial light. Artificial lights vary by the way they produce light. Incandescent light bulbs, fluorescent light bulbs and halogen light bulbs are among artificial light sources that can be used for plant growth.

The above three types of light bulbs vary by their cost, consumption of electricity, light intensity, heat production and color of light or wave lengths. In this project we compare these three types of light for plant growth.

Information Gathering:

Find out about different types of artificial lights. 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. The following are samples of information that you may gather.

Plants need light. Leaves produce the plant’s food (sugars and starches) from carbon dioxide and water by the action of light on a green pigment (chlorophyll) contained in their cells. This process is called photosynthesis. Large chlorophyll molecules absorb red and blue light from sunlight to get needed energy for photosynthesis and discard green light by reflecting it. That’s why trees look green during the summer.

So, just any old light won’t do. The light must contain red and especially blue, which, of course, sunlight contains. Plants thrive under the Sun since they evolved to its available light.

An ordinary incandescent light bulb radiates poor plant light since it is deficient in blue. Fluorescent bulbs, shedding more blue, are better. Metal-Halide (even more blue) and High-Pressure-Sodium (red) bulbs are better still.

By the way, incandescent light bulbs also contain a higher ratio of infrared to red light than sunlight. “This promotes stretching of plants,” says Art Cameron, horticulture professor at the University of Michigan.

Stretching helps seedling forest plants. Green leaves on mature trees absorb red and reflect infrared from sunlight. So, as the light descends to the forest floor, it contains more and more infrared. Consequently, young samplings, growing in this light, stretch and eventually reach red-rich sunlight.

Light quantity is the overriding factor. “It is nearly always better to have more light of the wrong color than less light of the correct wavelengths,” says James D. Hooker of Lighting Equipment News, University of Wales, UK.

Different types of light bulbs:

Incandescent light bulbs have a filament that gets very hot and emits light. Fluorescent lights, also known as gas discharge tubes, emit invisible UV lights that changes to visible light by fluorescent material coated inside the light bulb.

A halogen lamp also uses a tungsten filament, but it is encased inside a much smaller quartz envelope. Because the envelope is so close to the filament, it would melt if it were made from glass. The gas inside the envelope is also different — it consists of a gas from the halogen group. These gases have a very interesting property: They combine with tungsten vapor! If the temperature is high enough, the halogen gas will combine with tungsten atoms as they evaporate and redeposit them on the filament. This recycling process lets the filament last a lot longer. In addition, it is now possible to run the filament hotter, meaning you get more light per unit of energy. You still get a lot of heat, though; and because the quartz envelope is so close to the filament, it is EXTREMELY hot compared to a normal light bulb.

http://howthingswork.virginia.edu/incandescent_light_bulbs.html

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 compare the effect of different types of artificial 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 is the type of artificial light (Incandescent, fluorescent, Halogen).

Dependent variable is the rate of plant growth.

Controlled variables are temperature, wattage, type of plant, water, nutrients, exposure time, and experiment procedures.

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: Growing plants under different artificial light sources

Introduction: In this experiment you will grow seeds under 3 different light sources while keeping all other conditions identical. As for the seed, you can choose a grain or any of the commonly used beans such as lentil or lima beans. You will grow each plant in a separate cabinet. The cabinet can be an empty carton box or a wooden cubic frame covered with aluminum foil or white material (Paper or fabrics); Whichever you choose, it should be open to air flow. For light source, you can use any combination of one or more light bulbs of the same type in each cabinet; however, the total wattage in all cabinets must remain the same. For example, you may use two 30-watt fluorescent bulbs in one cabinet, one 60-watt incandescent light bulb in the second cabinet, and three 20-watt halogen bulbs in the third cabinet. Make sure that the light is evenly distributed in each box. White color or aluminum foil coatings inside the box helps in distribution of the light.

Procedure:

1. Get four same size plates and label 3 of them with the types of artificial light that you want to test. Label the last one as control.
2. Place the seeds in water for about 24 hours.
3. Fill up each plate up to 1 inch with wet seeds and cover the seeds with a wet paper towel.
4. Keep all four plates at room temperature and next to a window. Inspect the plates every day and add water to them or spray them with water to keep them moist until all seeds germinate (3 to 7 days).
5. Prepare three same size light boxes or light cabinets with three different light sources and the same electricity consumption rate.
6. Place three of the plates in the light boxes based on their label. The control plate will remain in the room without any extra light. At this point remove the wet fabric or paper towel from all dishes and turn on the lights in all three light boxes.
7. Inspect the dishes every day and add water if needed. Measure and record the height of each plant and record it in your data table. continue this for about 7 to 10 days.

Notes:

A wooden frame can easily be covered with white cotton fabric or aluminum foil. If you are going to use wooden frames, make all of them the same size. Also make sure that the light will be at least one foot away from the plant. When covering the box, leave sufficient openings for air flow. Plants need carbon dioxide from air to grow. Openings will also allow the excess heat to exit.

Incandescent lights and halogen lights create heat, and excess heat can damage the plant. Use them with reflectors and mount them faced to aluminum foil, so only the indirect and dispersed light will get to plant.

A wooden frame can easily be covered with white cotton fabric or aluminum foil. If you are going to use wooden frames, make all of them the same size. Also make sure that the light will be at least one foot away from the plant. When covering the box, leave sufficient openings for air flow. Plants need carbon dioxide from air to grow. Openings will also allow the excess heat to exit.

For this beautiful plant that you see in the right, I used my desk lamp. A desk lamp is adjustable at different heights and has it’s own reflector, so I did not need a box or frame.

I was also able to purchase a 60-watt halogen light bulb and a 60-watt condensed fluorescent light bulb with screw base matching my desk lamp.

If you can find same size (Same wattage) screw base light bulbs, you may simply use three desk lamps instead of 3 boxes. Also since desk lamps have a good reflector, you may also skip or simplify covering your setup with foil or white cloth.

Materials and Equipment:

List of material can be extracted from the experiment section.

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.

Record your experiment results in a table like this:

Plant height under different artificial lights

You may also use the above data table to draw a line graph. Use a different color line for each light. The plants height can be recorded in millimeters for the highest accuracy. You may optionally have other data tables for other plant conditions such as color or density. Properties such as color or density may be visually estimated.

Calculations:

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.

Conclusion:

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.

References:

While gathering information for this project you may study botany books and biology books with chapters about photosynthesis and growing plants using artificial light. List such books and references as your bibliography.

Following are some of the books that may be reviewed to gather information for this project.

Growing plants in artificial light, (National Lending Library for Science and Technology. Translation of Russian book). ISBN: 0853500290

The Indoor Light Gardening Book (Hardcover)

by George Elbert, ISBN: 0517500957

You may also use the following online resources:

http://howthingswork.virginia.edu/incandescent_light_bulbs.html

http://www.gchydro.com/

http://www.hydroponics.net/grow-lights.asp