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High Pressure Sodium Systems
    The most impressive fact about the 600-watt high-pressure sodium lamp is that it produces 90,000 initial lumens. The HP sodium is also the most efficient HID lamp available. It comes in 35, 50, 70, 100, 150, 200, 250, 310, 400, 600, and 1000 watt-ages. Nearly all of the HP sodium bulbs used in grow rooms are clear. All HP sodium vapor lamps have their own unique ballast. High pressure sodium lamps are manufactured by: GE (Lucalox), Sylvania (Lumalux), Westinghouse (Ceramalux), Philips (Son Agro), Iwasaki (Eye), and Venture (High Pressure Sodium). American growers use 1000 and 600-watt HP sodiums most often, while European growers love 400 and 600-watt HPS lamps.
    High pressure sodium lamps emit an orange-tinged glow that could be compared to the harvest sun. The color spectrum is highest in the yellow, orange, and red end. For many years, scientists believed this spectrum promoted flower production. However, with the new PAR technology, scientists are rethinking old theories. Marijuana’s light needs change when flowering; it no longer needs to produce so many vegetative cells. Vegetative growth slows and eventually stops during blooming. All the plant’s energy and attention is focused on flower production so it can complete its annual life cycle. Light from the red end of the spectrum stimulates floral hormones within the plant, promoting flower production. According to some growers, flower volume and weight increase when using HP sodium lights. Other compelling evidence shows the SunMaster halides to be superior. Growers using a 10 × 10-foot (3 m 2 ) room often retain the 1000-watt halide and add a 1000-watt sodium during flowering. Flowering plants need more light to produce tight, full buds. Adding an HP sodium lamp not only doubles available light, it increases the red end of the spectrum. This 1:1 ratio (1 halide and 1 HP sodium) is a popular combination for flowering.

Color spectrum of Cool Deluxe Sunmaster bulb

Color spectrum of Neutral Deluxe SunMaster bulb

Metal Halide bulb showing reaction.

Color spectrum of Warm Deluxe Sunmaster bulb

Base Up (BU) and Base Down (BD) metal halide lamps must be vertical to operate properly. Horizontal (H) lamps must orient the arc tube horizontally to burn brightest.
Operation and Construction
    High pressure sodium lamps produce light by passing electricity through vaporized sodium and mercury within an arc tube. The HP sodium lamp is totally different from the metal halide in its physical, electrical, and color spectrum characteristics. An electronic starter works with the magnetic component of the ballast to supply a short, high-voltage pulse. This electrical pulse vaporizes the xenon gas and initiates the starting process that takes three to four minutes. Electricity passes, or arcs, between the two main electrodes. If the lamp is turned off, or power surge occurs and the lamp goes out, the gases in the tube will usually need to cool three to fifteen minutes before restarting is possible.
    Similar to the metal halide, the HP sodium has a two-bulb construction, with an outer protective bulb and inner arc tube. The outer bulb, or jacket, protects the arc tube from damage and contains a vacuum, reducing heat loss from the arc tube. The sodium, mercury, and xenon gas are contained within the arc tube and have a constant operating temperature. The lamp may be operated in any position (360 degrees). However, most prefer to hang the lamp overhead in a horizontal operating position.
Life and Lumen Maintenance
    High pressure sodium lamps have the longest life and best lumen maintenance of all HIDs. Eventually, the sodium bleeds out through the arc tube. Over a long period of daily use, the sodium to mercury ratio changes, causing the voltage in the arc to rise. Finally, the arc tube’s operating voltage will rise higher than the ballast is able to sustain. At this point, the lamp will start, warm-up to full intensity, and go out. This sequence is then repeated over and over, signaling the end of the lamp’s life. The life of a 1000-watt HP sodium lamp will be about 24,000 hours, or five years, operating at 12 hours per day. Replace HPS bulbs after 18 to 24 months to keep the garden bright.
HP Sodium Ballasts
    Read “About Ballasts.” A special ballast is specifically required for each wattage of HP sodium lamp. Each wattage lamp has unique operating voltages and currents during start-up and operation.