Lighting for you cannabis grow is a crucially important factor, especially since cannabis uses different wavelengths of light in greater or lesser quantities depending on its stage of growth. During the flowering stage of growth cannabis soaks up what is known as warm, red light which is produced at the higher end of the spectrum. Again, although some growers use compact fluorescent lights (CFLs) for the flowering/budding stage of their grow, the most popular (and arguably the best) light for this stage of growth is a high-pressure sodium (HPS) light.
High-pressure sodium bulbs, like metal halide (MH) light bulbs, are a member of the high-intensity discharge (HID) family of lights. As a result, like the MH lights popularly used for vegetative stage growth, HPS lights require a ballast for proper functioning. They also produce quite a bit more heat than MH and CFL light setups, but they are truly the best bulbs for use during the flowering stage of growth.
Regarding the relatively high cost, if you are a grower on budget then you can get away with using HPS lights for your vegetative and flowering stages of growth, though the vegetative stage may last longer with a HPS bulb. So if you can only afford to invest in one decent light, a quality HPS system is the way to go.
Like MH lights and other HID bulbs, a HPS lighting system will consume more electricity than a CFL system, but HPS lights offer superior lumen output and exceptional bud results. The average lumen output for a HPS light bulb ranges from a low of 80 to 90 lumens per watt to a high of up to 150 lumens per watt, so a 100-watt HPS bulb will yield an average of 8000 to 15,000 lumens. HPS bulbs are generally sold as 250, 450 and 600 watt bulbs, with a range of other wattages available if you wish to further personalize your grow.
Cannabis is a very light loving plant, and during the vegetative cycle of its growth will flourish when receiving 4000 to 6000 lumens of light per square foot of grow space. During the flowering stage of growth, however, when your light schedule is on a 12/12 cycle, your plants will flourish and do well with 5000 – 8000 lumens per square foot of grow space.
There are many reputable manufacturers of lighting and various growing equipment, but for HPS bulbs specifically, some of the best manufacturers to consider include Hortilux, Lumatek, Sunmaster and Solis Tek. One particularly popular and well-reviewed manufacturer is Ushio.