HPS Lighting for Cannabis Plants
The major consideration to growing under high pressure sodium
alone is that the plants tend to be taller and leggier with a longer internodal length (spacing between branches) than plants grown under the bluer light of metal halide. Another factor to consider is that plants generally do not appear very healthy growing under HP Sodium light. The operative word being 'appear', because in fact most plants do grow very well under HPS lighting. As a result of the poor color rendering characteristics of high pressure sodium, the plants tend to look pale, washed out or nitrogen starved.
The benefits of high pressure sodium lighting include
an incredibly long usable bulb life... up to two years in most cases; and unparalleled efficiency at six times more light output per watt of energy consumed than a standard incandescent bulb. Due to their high efficiency and the fact that plants grown in greenhouses get all the blue light they need naturally from the sun, HP Sodium lamps are the preferred supplemental greenhouse light. Many indoor gardeners will grow their crop under metal halide lamps to keep the plants more compact during vegetative growth and then switch to a high pressure sodium system for the fruiting and flowering stage to increase yields and fruit quality.
Combination HPS/MH lamps
combine a metal halide bulb and a high pressure sodium bulb in the same reflector, either with a single integrated ballast assembly or two separate ballast assemblies. The combination of blue metal halide light and red high pressure sodium light creates an ideal spectral blend and extremely high outputs.
Beware of no-brand and do-it-yourself lighting kits.
Paying a few dollars more for a system that meets the high standards of safety set by Underwriters Laboratories could save that amount many times over should a shoddily manufactured lighting system cause a fire in your house.