HPS (High Pressure Sodium)

HPS (High Pressure Sodium) lights were the dominant indoor cannabis cultivation light source from the 1980s through the mid-2010s, responsible for nearly every famous strain, breeding program, and yield record from that era. The technology: HPS bulbs use an electrical discharge through pressurized sodium vapor inside a quartz arc tube, producing intense light heavily concentrated in the yellow-orange spectrum (560-620nm). This spectrum coincidentally matches one of the photosynthetic absorption peaks of chlorophyll, making HPS particularly effective for the flowering stage of cannabis. Standard HPS sizes: 250W, 400W, 600W, and 1000W bulbs are most common; 600W is the sweet spot for residential cannabis (best efficiency per watt with lowest heat density per square foot). HPS operating characteristics: light output 130-160 lumens per watt (high efficiency); spectrum heavily weighted toward yellow-orange, with weak blue and UV output (poor for vegetative growth, optimal for flowering); operating temperature very high — bulbs reach 800°F+ surface temperature, requiring 18-24" distance from canopy minimum; significant infrared and heat output (about 70% of total wattage emerges as heat) requiring substantial cooling capacity; bulb life 10,000-24,000 hours depending on quality; bulbs degrade significantly after 50% of life expectancy and should be replaced annually for serious growers. Standard cannabis HPS yield benchmarks: 600W HPS in 4×4 ft tent at SCROG produces 400-700g per cycle with skilled cultivation (1.0-1.2 g/watt). Trade-offs vs LED: HPS produces 30-50% more heat than LED at equivalent canopy PPFD, requiring significant AC cooling; HPS bulbs cost less upfront ($40-100 per 600W bulb vs $400-800 for equivalent LED) but consume 20-30% more electricity over their lifetime; HPS spectrum is sub-optimal for vegetative growth (most growers historically used Metal Halide for veg and HPS for flower, requiring two separate light setups). HPS remains popular for budget-conscious growers in cool climates where the heat is welcome rather than burden. Modern LED has largely displaced HPS in commercial cultivation due to better efficiency, lower heat, and longer operational life.