Why do people use Metal Halide lights for vegetative growth and High Pressure Sodium lights for flowering?
Many people switch between bulbs for different stages of growth for a couple of reasons. First of all, Sodium bulbs have been known to make som plants grow leggy and stretched out because of the yellow to red spectrum that they give off. Metal Halides tend to keep these plants tighter with less space between internodes. So some growers use the Metal Halide lights during vegetative growth to keep the structural growth of the plant nice and tight. But they switch to Sodium lights when the plants begin to flower because the Sodium lights produce so much more light than the Halides. Even though the Sodiums do not have as good a spectrum as the Halides the intense light that is put off by the Sodiums aids in flower development and fruit set. Do not be fooled though, you can use either light throughout the life of a plant and get excellent results.
