High Pressure Sodium (HPS) lighting is the most desirable for your growing and flowering of marijuana plants. There is this misconception that using Metal Halide (MH) during the vegetative growth stage will dramatically increase the size and overall general size of the plant and the buds. Of course, there is much research into this subject, most of it is of non-significance because unless the testing was directly done on a marijuana plant ( and even then strains differ greatly) it is mostly a bunch of mumbo jumbo that won't affect your growing at all.
The reason that it is irrelevant is because of the nature of the Marijuana plant. A marijuana plant can be anything from a herb looking shrub to a 35 foot tree that is so huge it is unnoticable as a marijuana plant at first glance. Marijuana strains come in short dark purple, all the way to the other end of the bright, light green super tall spectrum of the natural rainbow.
Marijuana plants will give more dried bud per watt when using hps lighting. The benefits of using metal halide during the vegetative stage of the plant is not worth the switching of the lights or the extra cost of the runnig the lights to bring about some illusionary result.
The mythical benefits of using metal halide lighting can be accomplished through selective breeding and overall testing of strains for the desired location.
Tighter buds and closer internodes are said to be the result of metal halide lighting. I can tell you this in my more than 13 years of growing marijuana , I have found that the result of tighter buds can be created through lower temperatures, better ventalation and strain selection. The short benefits to growing with metal halides are not only illusive, there are hard to document as simply switching your strain puts you in the tighter bud category. Lower you temperature and watch your buds tighten up.
When running a grow room a little hotter than normal to increase on the co2 uptake and maximize the yield potentiol, there might be the chance of your buds becoming a little fluffle because of the high heat to warm the co2 gas for best intake into the plants organism. The solution is simple, there just needs to be a cooling down period before harvest. The plants need about a good week or so to tighten up the buds. So if your temperature indoors is up to 80 or 85 for maximum co2 uptake, all you need to do is simply cool your room down to 75 to tighten up the buds. The co2 should still be dispensed into the atmosphere to help with the tightening of the buds.
Make sure to use a reputable type of brand light bulb for your hps needs that is of the most adequate light output. There are many bulbs on the market, most have great light spectrums, but very few have the best. I would suggest the hortilux bulb. The small difference in the spectrum has an astronomical impact on the overall growth when compounded in a large grow room. Remember Grow HPS!
