Thanks for the detailed response Delps8.
I'm using a Infisice Quantum PAR meter. The current PAR reading is 425-430 at the top of the plants. The lights are two (2) HLG 350 Diablo's, placed 34" above the plants turned to about 50% available wattage, or the 5th of 9 positions. My temps are 65-67 lights out and 71-77 on. I'm trying to keep the humidity between 50-60%, but it can drop to 40% occasionally.
Would you lower the lights, turn up the wattage, or just let the plants grow into the light?
Good info, thank you. And knowing the spectrum of the HLG helps a lot.
That's a great environment. Good to see that you're using a PAR meter, though that meter could be reading a bit low. If you have/can get use of iOS phone, download a copy of "Clear Sky Calculator". That's an app that Apogee has released that will allow you to calibrate any PAR meter. Some of the low cost PAR meters on Amazon use a gallium arsenide sensor that doesn't read light above 660nm. If that's the case with your meter, the readings could be low because, based on the spectrum, the Diablo puts out light above 660nm.
I'm surprised your light level is only 425+µmols-I was expecting that your were up in the 600+ range with plants of that shape but the Diablo has a good amount of blue in its spectrum and blue is what keeps plants short and encourages them to produce lots of stems and leaves.
My advice, and I practice what I preach (and I'm the first to admit I will "Preach it!"), is to get your plants to the light saturation point as soon as you can. The light saturation point ("LSP") in cannabis is 800-1000µmols. With a high quality grow, you will be able to ramp up very quickly - no reason not to jump in quickly.
HLG's tend to have a hot spot but with 2 of them, you're probably getting a pretty good pattern. Have you mapped out your readings? It would be very helpful for you to take readings across the canopy because that data can drive your decision about hang height vs dimmer setting. The goal would be to have all of your canopy at 800-1000µmols but we know that's really hard to do. Canopies aren't flat and lights do not put out consistent light from center to corner so that's where sampling the canopy comes in.
I grow 1 plant in a 2'x 4' and as the plant matures, I sample more areas on the plant. The 10 samples below are from an auto in week 6 of flower and it's in pretty good shape. The standard deviation for the canopy is only 40µmol or a DLI of 3 but we know they're not all like that.
If you create a table like this in Excel, you should be able to find the right combo of hang height and dimmer to get you where you want to be.
