Grow Journal of the Month: July 2020
From personal experience, I switched from 4 x 315w CMH fixtures just before i switched to flower, to 1920w of Citizen clu048 1212 cobs ( 24 x 3500 and 12 x 3000k, only ran at 1200w ) in a 2.4 x 1.2m tent, and it shocked the shit out of the plants and they just stalled for 10 days.
I dont know the science behind it, and im not gonna proclaim to be an expert grower, ive rand HPS, MH, CMH, COBS and QBs, but I wouldnt do it again.
Anyone know why ?
I got rid of the CMH's and veg with QB's and flower with COBS now.
your intensity may not be where you want. that's a lot of cobs. the drivers are super important. mean well or pairu are the only ones i'd run and they have to be paired with the cobs. over driven but under powered seems to be key if that makes sense.
i run the exact same cobs, but dimmable drivers . 200 watts for 4 cobs in a tad less than 4 x 4. previous when i ran other lights (hps, mh) and switched to cob, i always dialed the cob back a bit to start, and only ran 50- 60% until i saw how the plants reacted, then incrementally upped the intensity.
cob and qb light is different to any other, even burple led. it is very directional and intense. as a result you can get light burn, something akin to heat burn, but without the heat lol. cob and qb light will pass right through leaf vegetation, unlike hid type light. this displaces molecules in the leaf, and causes what is experienced as light burn (not heat burn, but does look similar to a degree). there is some science to back this line of thought.
in my first experiences with cob i was always burning the plants up. much worse for seedling and veg than in flower, but it did it at any stage. until i learned how to use the light it was a bit frustrating. cob and quantum light intensity also doesn't seem to diminish as much as HID does with distance. i actually had to learn to use the dimmer in tandem with distance.
i only just started using cob for all stages, as i did seedlings and early veg under t5's exclusively, until recent. learned that style over 30 years ago and never got out of the habit. i no longer have the room for 4ft fixtures tho. now, i'd never go back since i can do it all with one light and save energy costs.
currently i run my cobs higher than most, about 42 inches above canopy, and find this works until they get established and can handle the type of light i feed them. i simply adjust with the dimmer. from about mid veg forward they can usually take all i can give them, but i am near paranoid as to how they react to the light now (like waaaayy too paranoid lol).
i cannot speak for all, but this has been what my personal experience has been. i do work with led in another life tho and can attest to its throw, intensity, bounce, and penetration.