Why do people use Metal Halides for vegetative growth and High Pressure Sodiums for flowering?
A. People switch between bulbs for different stages of growth for a couple of reasons. Sodium bulbs have been known to make some plants grow leggy and stretched out because of the yellow to red spectrum that they give off while Metal Halides tend to keep these plants tighter with less space between internodes. Therefore, growers use the Metal Halide lights during vegetative growth to keep the structural growth of the plant nice and tight and switch to Sodium lights when the plants begin to flower since 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.
