Of these, light is usually the limiting factor, especially in schoolrooms where outside windows are small, face the north, or not present. Growing under lights relies on the intensity, quality, and quantity of light produced by fluorescent lamps. One foot-candle is defined as the light produced by a single candle 's flame as measured at a distance of one foot. Plants can be grown very close to the lamps without heat damage. Fluorescent lamps are usually suspended a few inches above the plant leaves.
Blue light provides energy for photosynthesis.
Red and far-red light are important for flower initiation. Combining one of the plant growth lamps with three, cool white lamps per four-lamp fixture will provide good spectral distribution. The intensity of light cast on plants' leaves and the duration are important to the maintenance and growth of those plants. Seedlings require 16 hours of light. Flowering indoor plants require 14-16 hours of light.