High pressure sodium lamps emit an orange or amber looking light. Their spectrum is heavily concentrated in the yellow, orange, and red spectrums with only minimal amounts of blue spectrum. These type of lamps are commonly used in street lights.
High pressure sodium lamps are usually used for flowering because they supply more orange and red light than metal halide lamps. Using lamps with increased orange and red spectrum seems to promote more flower production. Some newer HPS lamps emit enhanced levels of blue light, which encourages stout short stems and branches. Manufacturers of these lamps claim that the bulb can be used in both the vegetative and flowering stages.
High pressure sodium bulbs are available in – 150w, 250w, 400w, 430w, 600w, 750w, and 1000w sizes. The bulb wattage must match the ballast wattage.
“DON’T” use a smaller wattage bulb in a larger wattage ballast, unless the ballast has adjustable wattages, and you adjust the ballast to the bulb wattage.