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Botany science fair project:
Test the effect of temperature and light on plant growth

Science Fair Project Information
Title: Test the effect of temperature and light on plants growth
Subject: Botany
Grade level: Primary School - Grades K-3
Academic Level: Ordinary
Project Type: Experimental
Cost: Low
Awards: Second Place, Canada Wide Virtual Science Fair (2010)
Affiliation: Canada Wide Virtual Science Fair
Description: Soaked bean seeds were planted in four different pots, watered and placed under varying warmth and light conditions, plant growth and development was recorded over time.
Link: http://www.virtualsciencefair.org/2010/shaixs2
Short Background

Effect of Temperature on Plant Growth

Most houseplants are tropical species selected for their adaptation to growth in a climate which ranges from 15 C to 25 C (60 F to 80 F), similar to the temperature in most homes. Temperature control for other plants with differing requirements needs attention to heating and/or cooling.

Effect of Light on Plant Growth

Through the process of photosynthesis, plants convert the energy in sunlight to chemical energy, which fuels plant growth. The two important factors for providing light to a house plant are intensity and duration.

Different plants require different light intensities. Intensity (or quality) of light is difficult to measure without a light meter. It is usually measured in units of lux. 100 lux or less is usually considered "low intensity" or "indirect" lighting. A bright office has about 400 lux of illumination. 1,000 lux or more is usually considered "high intensity" lighting. Direct outdoor sunlight is in the range 32,000-100,000 lux. Foot-candles are also occasionally used.

The duration of light exposure is as important as the intensity. Quality exposure of 8 to 16 hours is ideal for most plants. Photoperiodism must also be considered, since some plants such as Poinsettia and Schlumbergera are influenced by either decreasing or increasing daylight hours.

Windows are the most common sources of light for houseplants. In the Northern Hemisphere, south-facing windows have the most sun exposure, while western, eastern, and north-facing windows have progressively less exposure. Natural sunlight through windows is affected by seasonal changes, cloud cover, and window treatments. The length of time that light is provided will determine how the plant grows. Providing 16 hours of light/day will promote strong roots, stems and abundant leaves. Decreasing that amount to 12 hours of light/day will signal that the short days of Winter are coming so the plant energy will focus more on flower production and less on green growth.

Artificial light sources can provide an alternative or supplement to window lighting. Fluorescent lighting provides excellent light quality whereas standard incandescent bulbs do little to promote plant growth. "Cool", or "blue", fluorescent lights at 6500k provide the light needed for lush green foliage plants, while "warm", or "red", fluorescent lights at 3000k provide the light needed for blooming flowers and fruit production. Warm whites are better for flowering plants while cool whites are more suitable for green, leafy growth. When used together, these bulbs are closer to the full spectrum light that comes from the sun, although less powerful.

There are several types of lighting units which can sustain indoor plants. Choosing the best type depends on the need of the plants grown and/or your budget. For the sake of efficiency, incandescents, no matter how cheap, should not be used. Not only do they provide little or no benefit to plants, but the cost of the electricity will outweigh the cost of purchasing multiple incandescent bulbs and fixtures in the long run. Fluorescents are your safest bet. CFL fluorescents are the cheapest option, but more than a couple bulbs are almost always required to be running at once. The next step up is shop lights, available mostly in 2-ft. or 4-ft. fluorescent tubes. The best type of fluorescent are called High Output Fluorescents. Also available in 2-ft and 4-ft. tubes, these bulbs provide more wattage (54 watts each is standard) thus more lumens per watt (92 at the current time). That's about 5,000 lumens per dual 4-ft H.O. Fluorescent Unit. The most serious lights that are used by professionals and in greenhouses as a supplement, are known as Metal Halide or High Pressure Sodium Grow Lights. These lights provide the most lumens, heat and intensity of light so they should be positioned respectively further from the tops of plants to prevent burning.

See also: http://en.wikipedia.org/wiki/Houseplant

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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Last updated: June 2013
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