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Q&A: Biological Clock

What is the biological clock of tomato plants so that we can induce the plant to flower? How much light (X numbers of daylight hours and Y numbers of darkness), and at what stage ( Z numbers cm tall) is the best to induce it? Should one cover the plant in a black plastic bag for the remainder of the 24 hour period? That is what I understood being done by the Florist to force/induce the plants to flower at any time of the year, by manipulating the biological clock of these flower plants, but then they will not reveal the biological clock to anybody because it is their bread and butter in selling flowers.
Tomatoes grow best at 4000 lux, 18 hours a day.
Works well with 16 hours of light.
My indoor tomato plants are doing quite well with 12 hours of light. Sometimes they get less, sometimes they get more. I try to put a little randomness into the process to copy the patterns of cloudiness, etc. (Basically I do not have the lights on a timer so I often forget when I turned them on) Also I don't believe there is a magic height that they have to attain in order to start blooming. I keep mine trimmed to 18 inches tall because that is as high as I can raise my lamps and I have blooms on every one of my 6 plants and three small green tomatoes as well. I built the 'incubator' for seedlings and have no other means of growing these tomatoes indoors. I use 4 40W fluorescent bulbs (4 foot long).