swapping out HPS 400w for MH while flowering..

I currently am in week 4 of flowering. I have read many times that running both MH and HPS at the same time is optimal for plant growth through the plant's entire cycle. I have a 400W HPS bulb running to emit the red spectrum right now that I was considering swapping out with my other metal hailide bulb that I started with during veg. My question is: would switching back to a metal hailide bulb at week 4 in flowering do more harm than good or could it possibly make the buds more compact? - something I have also read.

Thanks for your input.

I dont see any point in switching back to an MH bulb now, as dual spectrum is using both simultaneously. Both MH and HPS will veg and flower plants just fine - some people have preferences.

If you can add the MH into the setup as it is now, then you should definitely see the benefit - but I don't think I'd worry about swapping them at this point

i could be wrong but i thought mh was great for veg..then hps for flower

correct ... for best results: high-K light from either fluoros, or Metal Halide, for vegging, and low-K light from a HPS (sodium) lamp, for flowering ... :smokin:

Another from Vatican city? What're the odds ;)

The "general" rule of thumb is MH for VEG, HPS for flower. This is not a hard and fast rule though, just a guideline. I know growers who use MH alone all the way through and swear by it, and others who use HPS all the way through and swear by it. With all the different enhanced spectrum bulbs, and cfls and everything that are available, its hard to say theres a rule

I personally have found that using both MH and HPS through all stages enhances growth positively in a number of ways..

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Originally Posted by Tokudai

I personally have found that using both MH and HPS through all stages enhances growth positively in a number of ways..

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I guess that's the consensus then. What I was trying to determine was if the buds could get more compact as a result of using the MH bulb I started with (through veg). I guess just running both at the same time is the only real way to go.

while any light will grow a plant, the plants prefer the reddish spectrum during flowering ... it looks like the waning sunlight, as Fall nears, to the plant, triggering it's flowering/seeding phases ... simple: MH=vegging, HPS=flowering ... :smokin:

All of the "best" bulbs are enhanced spectrum - adding more red to MH lights, and the enhanced HPS lights add more blue. Its growing obvious that both spectrums are the best choice for the plant. The light cycle itself triggers the flowering phase, not the spectrum of the light.

I'd like to see some studies that show that plants respond to HPS more than MH when flowering. I know its "a known fact" but then again so are hotspots from foil - but show me someone you actually know that has experienced it (burns from a wrinkle in the cabinet liner). Some of the old school growers I know only use MH lights, and produce some incredible nugs.

light is a very complicated subject, to really even begin to understand how it works you have a lot of reading ahead of you, i would suggest looking more into horticulture literature and not just cannabis, pick up some maximum yeilds as well, very good info in those, now to begin to grasp the reason for the MH and HPS combo switch you need to understand what these lights do and how the plants use them, for one your typical HID lamp such as a 1000watter only offers somewhere in the lines of 350-380 usable watts, these watts are called PAR watts (photosythetically actyive radiation), now depending on your choice of application whether it be HPS or MH you need to be able to differ the 2 spectrums, MH puts off a lesser PAR wattage but the spectrum is more usable by the plant, MH give you more ideal growth at a slightly slower rate, this is why some old schoolers prefer MH throughout the entire grow, i guess as you get older you understand the value of patience for quality, now on the other hand HPS puts off a higher PAR wattage so there is indeed more usable light but the spectrum is a bit weaker then MH, thus why people say HPS is more efficient than MH, it is, HPS will give you a much accelerated growth rate and definatley do the job in my opinion, but some old schoolers will tell ya the quality of bud with a MH is much better, but to a new grower who hasnt yet tweaked his enviroment to perfection will not be able to tell this difference