Here is a supportive article a friend of mine wrote:
The Importance Of Mixed Lighting (Dual Spectrum)
It is common knowledge that plants absorb warm and cool spectrum of light throughout its life. But I find that the importance of mixed lighting is understressed throughout the growing community.
During the flowering phase of a plants life, Warm light is better utilized to increase the size of a plant's buds. As CFL growers we tend to pile up on 2700k bulbs to increase our yield. In most cases, growers assume that warm light not only grants us larger buds, but insures that those buds are of connoisseur quality as well. This is not to say that one can not achieve a very successful crop off of pure warm spectrum 2700k lighting. We see it all the time as members of the Grow Forum Internet community. But as CFL growers, almost all of us demand a higher efficiency for our dollar.
So what does this mean? Clearly I'm trying to emphasize the necessity of cool lighting during the flowering phase of a plants life. But why? Well thats simple. As many of you may have heard or read before, Cool lighting (6500k) introduces a UVB spectrum that benefits the potency of the buds our plants are producing.
" The writer's own experience allow for a more specific conclusion: If the UVB photon is missing from the light stream(a), or the intensity as expressed in µW/cm2 falls below a certain level(b), the phytochemical process will not be completely energized with only UVA photons which are more penetrating but less energetic, and the harvested resin spheres will have mostly precursor compounds and not fully realized THC(c).
Now it would be completely unreasonable to ask a grower using a 1000watt HPS to switch out for MH lighting even though it produces quality of the weed. Sticking with blue spectrum lighting in a plants flowering phase would greatly decrease the size of the buds and the yield of the plant. People using high wattage systems tend to grow for cash crop. No single person really needs a pound of buds.
" “Metal halide produce the best potent buds with less lumens for the money but better smoke. After years of testing with some friends who did want to keep THEIR recipe (more hps) I found their buds to be harsh, full of CBD, make me eat and sleep. The blue spectrum will give you a final product that have everything included:taste without curing, potency and yield.
For lower wattage growers who grow for self use, and are not on a low budget, it would be beneficial to replace their HPS with an MH for the last week or two of budding. This is because the last weeks of a plants life before harvesting is dedicated to the ripening of the buds, and not the growth of the bud itself. It would not greatly impact the yield of the plant, but have a great effect on the quality. Interesting, but this only applies to a few amount of growers that fit this category.
As CFL growers, we would be fools to ignore such information. It is astonishing that so many fantastic growers to not utilize cool lighting even to a small supplemental degree. We owe it to our selves to scrounge up a few bucks in change and take a drive to Home Depot. Buy a pack of 6500k bulbs (26watts tend to be popular, 42s are better) and set them somewhere not far off from your buds. Don't let your hard work return with unsatisfaction. Added quality with increased quantity(more light). Mixed lighting should be standard knowledge, not found in the advanced cultivation section.
Side Note: Reptile lighting found at pet stores is not ideal for UVB lighting. Yes they do emit a high % of UVB than regular CFLs but they output less light and emit over 12x more UVA light than UVB light which can harm your plant.
Contributed and submitted by Chase1126, and edited for links and spelling.
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