Plants love light, especially the Sun's
Q: What is the difference between sunlight and artificial light on plants-Quan, Sidney Australia
 A: 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 summer.
Right: [Mark Landers, Light Manufacturing Co.] A grow light
So just any old light won't do. The light must contain red and especially blue, which, of course, sunlight does. 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 as the light descends to the forest floor.
Consequently, young samplings stretch and eventually reach red-rich sunlight.
The quantity of light 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.
(Answered by April Holladay, science correspondent, July 11, 2001)
Further Surfing:
Michigan State U: Light and plant growth indoors
Light Manufacturing Co.: Grow lights
The growing edge website, light basics
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