Hey DANGERDAN_ thanks for the additional information! And hey, that post wasn't intended to contradict any of the information you provided, but rather to condense what I've been able to gather from different research projects and personal experience.
All I know for sure is that the lights I got 3-4 grows ago have produced considerably heavier harvests in the same space with all other factors very similar. They are just too powerful for seedlings so I only use one & have to lower the intensity by raising it or adjusting the output itself. Since different strains seem to respond best to different light levels I watch the seedlings very carefully once they get their heads above the medium. If they appear to be stretching more than I like then I lower the light intensity and if the stems are quite short and the leaves small and dark then I raise them and that seems to make a big difference within a few days at that stage.
Then as they get going I light up the second and raise the output and/or drop them so they are closer as the plants mature. For most of the grow the canopy is getting between 500-700 umol/s which is in the range you suggest and seems to work best for me too.
For the last 2-3 weeks they get a bit more on the higher end- in the 700-900 range. This seems to result in a burst of size and density in the buds themselves that I wasn't seeing before. But I do need to watch them carefully so they don't get burned.
The slight increase in stress is also suppose to increase potency but I have no way to measure that. One of my main concerns at that time is burning up some of the terpenes themselves...so another reason I try to be careful. As a safety measure I try to make sure the temperature range stays between 65-75 F. and that air circulation is adequate to keep the top of the canopy from getting too hot. Fingers crossed! I'm getting close to that time in the present grow.
We measured the umol/m2/s every 6" across a square meter_ about 36 readings/meter2. The difference between each reading was less than 40 umol/s,..the results seemed to produce larger buds on all the colas, especially ones that were 6-12" shorter than the tallest ones and those on the outside of the space which weren't getting as much light with the first setup...
I'm certainly not a physicist and could easily be wrong or not completely understand how all these elements add up but having more even light coverage over the entire canopy and one that has better penetration into the canopy produced a significant benefit to how heavy the harvests have been since changing my lighting system.
The coverage provided by my first lighting system wasn't near as even or provided as much light or as full a spectrum and the harvests weren't nearly as good. When readings were taken with the same devise every 6" squared with that first lighting setup the intensity was constant for the square foot directly below each light but fell off quite a bit when measured out beyond that. The first lights didn't cover my space as efficiently as the ones I have now_ which cover my grow space of 3.5' x 6'.
These observations included about 11 different strains for whatever that might be worth..?.
At this point my harvests seem to be effected more by other environmental conditions and I don't feel they can be improved by changing my lighting. Training, the strains selected, medium, temperature, air flow and nutrient levels seem to be the major influencing factors at this point. And of course genetics.
Unfortunately the device that measures PPFD is too expensive for me to own one but we were lucky enough to borrow one about a year ago from a local commercial grow house supplier. It certainly did provide what seemed to be valuable information to dial in our lighting and was a good learning experience as well. With the first lighting system it appeared the canopy was receiving pretty even light but the meter provided information our eyes alone couldn't discern.Maybe letting us borrow the meter was just a ploy by the supplier to get me to invest in new lights! But I think not, considering the effect they have had.
One thing I love about growing is that you can experiment on so many different levels to see how different elements affect ones harvests within the constraints of different growing environments. The challenge is trying to get all these factors dialed in for optimum results....and then of course about the time that happens one finds they want a larger or taller area... or both a veg room and a bloom room_ my next objective for certain!
Thanks for all the information and cheers to new knowledge and awesome grows!
