HPS (High Pressure Sodium) grow lights are popular for indoor growers who grow high yielding plants.  HPS lamps are available in sizes from 250W, 400W, 600W and 1000W. There is also the choice of single and double ended lamps, and the older style 240V lamps compared to the latest 400V lamps - depending on your ballast. The orange spectrum promotes flowering and budding, as it mimics the glow of an autumn sun in the northern hemisphere.