Lighting Dimming for seedlings?

[Bekay]

First grow started under diy COB's. Do I need to dim these beasts?

• 4 COB unit. CXM22 (Color Temperature: 3000K 90CRI) run at 1400 mA for 75ish Watts ea. on a Mean Well HLG-320H-C1400B driver.
• Home made frame places COB's 15 inches on center
• 2 x 2.5 x 7 ft. high tent (300w over 5 sq. ft.)
• Currently placed at 40 inches above pots and running at ~40% output. This was measured using a lux meter app on my tablet. 19,000 lux max with coverage varying down to 17,500 lux across my small tent. I know these numbers are only relative but they did give me dimmer setting range and I was pleased with the uniformity of lighting. BTW full on 300W is really "get the sunglasses" bright!
• Today is the 4th day above the coco for my LSD-25 seeds and the first real leaves are still small

I don't know what might be too much light or too little. The seedlings seem to be of good color and somewhat stretching compared to my previous three Mephisto and a Med Gom 1.0 grows but these are different genetics. I expected there would be bigger leaves today but hey, I was looking at Hansbricks' LSD Grow Log. Not enough leaf yet to look for taco'ing so I am playing it careful. Has anybody fooled around with light height and intensity on young plants? Don't want the girls to shrivel up and quit.

 

[namvet25]

It's best to start out with lights higher and lower power at first than if you see the getting spindly or stretching move the light closer little by little until she stops stretching.This might take a little practice at first but practice makes perfect and you will learn as you go.

 

[Dr.Bubbles]

I am new to COBs as well, and it truly is the wild west of lighting, especially when you're using a homemade frame. Obviously there is no one size fits all method when everyone has different spacing between the lights...Or a 1050 to a 1400ma driver will make a difference as well. My advice is to just be smart and pay attention. Use a ruler for repeatable height over canopy, and if they start to bleach or curl then its gotta scale back a little. There is a PWM digital resistor with a screen that replaces the cheapie potentiometer that you would use with the "B" series Mean Well drivers to consistently scale power to the exact same number... Say 72% as an example. Very repeatable, and its only $40. Growmau5 YouTube channel is where I learned about this, and he has a link to the Amazon page to buy one if you are so inclined. Its a very recent video too, so won't be too far down the list of uploads. No stretch, no bleach, no cupping of leaves....Just keep a diligent eye on the crop and you will be fine. Nice looking build by the way.....COBs are hands down the best lights on the planet for what we do. Good luck on your new rig and welcome to the COB family.

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[Bekay]

It's best to start out with lights higher and lower power at first than if you see the getting spindly or stretching move the light closer little by little until she stops stretching.This might take a little practice at first but practice makes perfect and you will learn as you go.

Thanks, Namie. I guess that identifying a stretch is part of the art. I don't have enough experience yet. I was told by an AFN friend that ideally your nodes should be 1.5" to 2" apart. So until there are a couple branches that doesn't help me. If they keep pushing the stalk and first set of leaves up toward the light like 2 or 3 inches above the soil is that an early stretch indicating she needs more intense (closer and/or less dimmed) light?

 

[namvet25]

Seedlings grow very slow for the first couple weeks while there sending the roots down.If the seedling stem is over two inches high and she just looks thin stem it's time to move the light closer.

 

[Bekay]

Thanks Dr.Bubbles, all good advice and I will be keeping an eye on her and her sister. I like the Light Meter app I am using because even though it doesn't likely produce accurate numbers for lux (or maybe it does, doesn't matter) it does give intensity numbers and a graph over time. This allows me to move it around in the tent and get a relative coverage profile and also a dimmer setting that I can calculate percent of max. I also like that its free. Blew my summer allowance on the lights and a little MammothP.

 

[Bekay]

Seedlings grow very slow for the first couple weeks while there sending the roots down.If the seedling stem is over two inches high and she just looks thin stem it's time to move the light closer.

Perfect actionable advice. That's exactly what I needed to know. And why this forum of helpful brothers is so freakin' great! Thanks.
Just measure 1-1/8" and 1-1/4" and not too skinny legs. So I'll keep an eye on 'em.

 

[Dr.Bubbles]

Worst case with stretch....Just bend that bitch right over...Lol. I was playing with some Citi 1818s at about 35w each and they were a little too high and I got the dreaded stretch. So I tied em up and dragged em right back down. The stretch is now sideways, and the plants responded by sending up some more grow shoots off the bottom. Used the tie method on the new growth to pull that away. Bottom line, went from a complete embarrassment, to a trio of lovely ladies that are about a week to 10 days away from finishing. My very first COB grow and I CANT WAIT FOR ROUND TWO!!!!!!! Got some of the Illuminauto drop from Mephisto on the 4th of July drop and finally getting my spot all tuned up with cobs. Its a height limited space too, so HPS is out of the question....But these girls are looking pretty gorgeous. Small spaces with cobs and plant manipulation is something anyone can pull off. What a time to be a farmer....Lol

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[Bekay]

@Dr.Bubbles Got any pictures or a link to a grow log? I missed the Illuminauto drop but have some Mexican Airlines that will be next. I'm thinking just one in my small tent.

 

[Dr.Bubbles]

I will get some good pics. Maybe even tonight. I will put a picture up right here in this thread to make it easy. I haven't posted any pics on here yet, and was thinking about doing a possible log to score a badge or three. Might as well get first grow, COB snob, Mephisto strain report and all that...Lol. Its like achievements for Xbox. And I am sucker for those too. These 3 right now that I literally brought back from the dead are all Mephisto Walter Whites from a freebie grab from some Sour Stomper autos...Which is an INCREDIBLE strain. Everyone needs to try the Sour Stomp from Mephisto. Everything was wrong. I transplanted them....Which is frowned upon in true Auto form. I used a CRAZY hot soil that looked gorgeous, but had a shit load of N. Way too much for an Auto. This was also my very first auto grow as well, as I am more of an old school grower with HPS and photos and clones and moms and 2nd room and 12/12 lighting flower and 18/6 veg. These cobs along with the ridiculous quality of modern genetics, namely Mephisto Automatics is a whole new frontier. Besides that, I had MAJOR heat issues, which I have sorted out, they were in Solo cups inside a bucket for a week while shit got put together. Stretch, and just a bunch of little shit that adds up to a miracle that they turned out that way they did. 40 days ago I had my doubts. Next round is gonna hopefully by Canna Coco in decent sized Airpots with Canna A+B, CaMg and some Mammoth P. Got a chance to run a AVT special Kush pheno(Oh boy) and maybe Livers n Cheese or MBAP. Thinking about running just 2 ladies under about 150w or so of Citizen 1818s 90CRI @ 3500k in 5gal Airpots which I don't own yet but found a good deal on Amazon for 6 for $50. I expect some real good results and literally can't wait.

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