Efficiency: Fluorescent lamps (including GRO-LUX lamps) are about four times as efficient as incandescent lamps. This means that a 20-watt fluorescent lamp produces about as much light as an 80-watt incandescent
lamp, so it requires only one-fourth the electricity.

How Light Affects Plants
Plants use the energy from light for more than photosynthesis. The effect of light is still one of the most complicated questions in plant study today. The four aspects of plant growth most affected by light are:
• photosynthesis — converting
light, air and water into
carbohydrates and oxygen
• chlorophyll synthesis —
building the plant cells that
perform photosynthesis
• photoperiod — sensitivity to
the length of day
• phototropism — movement
toward a light source.

http://www.sylvania.com/forum/pdfs/faq0040-0800.pdf


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Note added at 8 mins (2004-03-31 16:20:32 GMT)
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Incandescent lamps provide red light but very little blue light,
while cool-white fluorescent lamps provide blue, yellow, and
green light but very little red light. As Figure 4 (above)
shows, both the regular and the wide-spectrum GRO-LUX lamps provide blue and red light in the proportions needed for photosynthesis.