If you think of different bulbs in terms of feeding your plants, Metal Halide is their chicken while High Pressure Sodium is their fish. Both are a good main course, but you want to mix it up every now and then to keep the palate interested. High-pressure sodium lamps heat up slowly, easing their way from a light pink up through a warm orange. Some plants respond very well to light of differing colors and warmths. Alternating between a Metal Halide and High -Pressure Sodium bulb every other week is a good way to give your plants the maximum amount of light to keep them healthy.