Question: I see all kinds of advice about growing under lights, but no one has committed themselves as to what type of florescent to use, “warm”, “cool”, or “grow-lights”. Would you help?
Answer: This is a subject which requires more than a paragraph or two to adequately address. We’ll keep the discussion simple for this reason (and because we’re far from experts in this area). Basically, the discussion revolves around two considerations: the light’s “color” distribution and intensity. Very simply, light of different wavelengths (“color”) are absorbed differently by the plant’s leaves for photosynthesis (for growth). It’s been found that light in the blue and red spectrum are most used by the plant. Artificial lights producing proportionally more light in these colors then, will presumably be more beneficial for the plant. Incandescent lights provide plenty of light in the “red” part of the spectrum, but these produce too much heat to be used successfully in growing violets–for them to provide enough intensity, they need to be placed close to the plants, but they give off too much heat to do this. “Warm” and “cool” white florescent bulbs generate less heat (and use less electricity) than incandescents and, though they provide light in the blue part of the spectrum, provide very little “red” light. “Grow” lights have the advantage of providing much more of this “red” light in a florescent bulb.
In practice, however, light intensity seems more important in growing violets under artificial lights. Many people grow excellent violets under the ordinary, “cool-white” bulbs available at any hardware or department store. So long as the plants are getting enough light (duration and intensity), the color spectrum seems of less importance. Our personal experience has been that there is little apparent advantage to using any particular type of florescent bulb. We’ve often grown our best showplants under supposedly the worst light–“cool” white bulbs. We do use “Gro-Lux WS” bulbs in our shop, but only because these bulbs most closely approximate sunlight so that the “perceived” color that the customer sees in the shop is close to what they’ll see at home in their window. These bulbs are also much more pleasant to work under for 12 hours a day.
Finally, don’t confuse light “intensity” with “efficiency”. A bulb using less electricity (watts) may simply produce the same light intensity (lumens) more efficiently. Again, why not save money? These measures can change bulb to bulb, so read the label when purchasing