How long should grow lights be kept on per day and how close to the plants should the light be kept?
For germination and seedling/plant growth, you want to simulate the natural day-night cycles, and as a general rule, grow lights should be on 8-12 hours per day and off at night. You can vary this timing, as some seeds such as tomato, pepper, petunia, impatiens, and others, benefit from 14-17 hours of light per day (and the remainder of the 24 hour period in darkness). The most common grow lights used are fluorescent; using cool white, warm white, and wide-spectrum fluorescent tubes. These lights work well for germination and for growing plants up to a transplantable size. Fluorescent lights should be kept close though, 3-6 inches above the soil or the growing plants, adjusting the height as the plants grow.