|MadSci Network: Botany|
Plants can use all colors of light in photosynthesis although green and yellow light are used less efficiently, often around 60% relative to red and blue if red and blue are considered 100%. Plants also use light in several other ways. Blue light is the trigger for phototropism, an example of which is the bending of plant shoots tpward light in a window. The plant pigment phytochrome is triggered by red and far red light. Phytochrome is involved in several plant processes such as etiolation (the extreme elongation of plant shoots when grown in the dark) and photoperiodism (daylength effects on plant flowering and dormancy). The study of light effects on plant shape is termed photomorphogenesis, and the Plant Photobiology website cited below has a detailed introduction on the subject. If you grew plants without blue light, you would expect them not to exhibit phototropism. Similarly, plants grown with no red light may be etiolated even though they would have sufficient nonred light for adequate photosynthesis. It is difficult for plant scientists, and basically impossible for students, to grow plants under different light colors and assure that the plants get the same amount of light from each color. Expensive equipment such as quantum sensors, light meters, and spectroradiometers are required to do this. If you do not have the same amount of light from each color, then you cannot tell if a reduction in plant growth with certain colors is caused by less light or by the color of light. One type of fluorescent lamp, termed Daylight, is very similar to sunlight in its color composition. The common Cool White flourescent has less red and far red than sunlight which makes plants slightly shorter. Incandescent lamps have much more red and far red than sunlight. High pressure sodium lamps are high in yellow wavelengths. The Plant PhotoBiology website contains a lot of info including spectral output by various electric lamps. Plant light questions come up a lot on if you search the Madsci archives you can find many other answers on plant light. References Etiolation Photoperiodism and Phytochrome Plant PhotoBiology
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