The two most common HID lamps are the halide and sodium types. Halide lamps are the most popular source of white light available for indoor gardening, providing the best light spectrum for all stages of plant growth. Not only is the light emitted from halide lamps comfortable to work around, but plants also appear most aesthetically pleasing when viewed under white light. The bulbs produce light up to six times more efficiently than incandescent light sources. They also have a long life expectancy and are available in a wide range of wattages.
Sodium lamps are the brightest of the high intensity discharge lamps.
Sodium bulbs are also available in a wide range of wattages and typically last longer than halide bulbs. Halide bulbs are recommended for situations in which there is little or natural light. Sodium lamps are best for supplementing natural light. Sodium conversion bulbs are available which can be interchanged with a halide bulb in a halide lighting system to boost flowering. This depends on the size of your growing area, the light needs of the plants you're growing and whether the artificial lighting will be the primary light source or a supplement to natural light.