Question: I grow some of my violets under artificial lights on a light stand very close to my kitchen window. My miniature violets are about 10″ below the tubes. How many hours should I keep the lights on?
Answer: We also grow our minis about 10″ below the tubes, with our standard-size varieties about 18″ below. Our lights remain on about 13 hours each day. These plants, however, receive no supplemental natural light. We do have two growing areas that receive a great deal of natural light as well.
The first of these are standard violets that we grow under florescent lighting on the lower shelf of a large bench in the glasshouse. During the summer, especially, these plants get a good deal of additional indirect sunlight. Because of this, we give them only 10 hours of artificial light during these months. We also grow many of our plants, including all of our showplants, in a room with many very large windows–the south and west walls are nearly all glass. Because we need to equalize our electricity usage throughout the day, we keep many of the lights turned on at night. As a result, the plants never really have a period of total darkness. From experience, we’ve learned that most of these plants do well only if lights are kept on for 10 hours or less, sometimes as little as 8 hours, a day.
A precise answer can’t be given, since it depends upon that particular growing environment. But it is safe to say that less artificial light needs to be provided in the presence of supplemental natural light.