Cob vs cmh

[Gjohnstone]

Buying some new lights and still debating between 2 100w COB lights and a 315w CMH. I have a 3x4 grow space and I typically only run two plants at a time. Grows are either soil with a Scrog or hydro with a four way topping and tying down. Any input/experiences on which way to go would be appreciated.

[az2000]

Buying some new lights and still debating between 2 100w COB lights and a 315w CMH. I have a 3x4 grow space and I typically only run two plants at a time. Grows are either soil with a Scrog or hydro with a four way topping and tying down. Any input/experiences on which way to go would be appreciated.

I grew a considerable amount with various LED fixtures (including ordinary LED household lightbulbs[1]). They definitely work. But, I didn't feel the finish quality was as good. (Crystals, aroma.). My product was kind of dry (not sticky, resiny. It was still good. If I hadn't grown with T5HO before using LED, I wouldn't have been very impressed.). I think it's because LED doesn't have UV like traditional lights. I used Reptile CFL bulbs for UV. But, that's a hassle. I never knew how much to use, how long, the lifespan of the bulbs.

I ended up liking T5HO at 40w/sq ft (45 in flower, with some LED household bulbs as sidelighting). And, CMH at 35w/sq ft (38 counting the ballast. And, again maybe supplementing with sidelighting in late flower.).

I produced a ton of dense bud using household bulbs at 28-32w/sq ft. And, there are high-quality LED fixtures that will produce at 22-25w/sq ft. The problem is, it's hard to find objective info about LED fixtures. There's a *ton* of flim-flam out there, selling for high prices. And, people who own it will defend it till the death. So, you can't go by testimonials. It's very religious. People will say "I love my [fill in the blank]." But, they won't provide objective info about w/sq ft, or the finish quality. (One guy was growing *amazing* buds under one scammy brand. He loved it. Everyone was justifiably drooling over the buds. But, nobody talked about how he was using 80w/sq ft! That's more than HPS! That's the kind of thing I saw *a lot* of. Nobody started from the proposition: "why do I need LED." They just got into it because it's the new-fangled thing. And then set about making it work -- with more light. The more they went down that path, the more defensive they were, evangalizing, etc.).

I didn't like anything about the LED scene, to be honest. Predatory sellers. Religious-minded buyers. Flame wars. Everyone with a hair-trigger to defend their "denomination." Very little was objective. It's a tough issue because, if someone likes running [fill in the blank] at 40-50w/sq ft, who cares? Part of growing is having fun. But, when someone is considering buying LED.... it was impossible to have rational discussions. (If it involved a sponsor of a forum, you could get banned.).

IMO, the only reason to use LED is if you live in a hot climate (or have expensive electricity). But, you'll have to spend a lot of money on high-end fixtures. The average stuff won't run cooler than CMH or T5HO. You'll probably have to run the average stuff at more w/sq ft. (Also, CMH has remote ballasts now. And, air-cooled hoods are available. It's also possible to replace the ballasts in T5HO fixtures with remote-mount ballasts. I can give more info about that. Or, call Fulham to discuss it.).

To me, traditional componetized/commoditized lights are better. No secret-sauce "spectrum." No drama. No team sports. I still use LED lightbulbs around the sides of the tent of sidelighting. I think LED lightbulbs are great for new growers. They can start small until they know they can grow. They don't have to go "all in" on a light fixture. And, whatever they buy can end up being used for sidelighting. It's not a dead-end.

[1] I hope it's ok to link to another forum. This is where I posted some info about my lightbulb grow, just so you can see how well it did. It just wasnt' top-shelf. https://www.thcfarmer.com/threads/co.../#post-2268754

[s62]

Really great answer! Have you used LECs before?

[FatBoy40]

am using a 630w CMH for Flowering and a 315w for veg. I am starting week 4 Flowering of my first grow with thw CMH. I am putting together a week by week photo book of the grow with CMH and will post when complete.

[D.A.A.S.69]

GoodMorning GJohnston,
You can grow some fine bud with Leds, just pick a good one, Cobs are fine.
I use both, 315cmh and Leds, but mostly 315cmh, and my plants, seem fine to me.
HappyGrowing

[Gjohnstone]

Thanks everyone! I should give more detail. I will be using RDWC, my two buckets are on 16” centres. My concern with the CMH is the with distance between the buckets, the light may loose intensity. With the 100w COBs I can place each light above the plant. Do I need to worry about the CMH loosing intensity over 3-4feet wide ? I cannot go to a large CMH due to heat concern in my grow space, that is a whole other story

[az2000]

Thanks everyone! I should give more detail. I will be using RDWC, my two buckets are on 16” centres. My concern with the CMH is the with distance between the buckets, the light may loose intensity. With the 100w COBs I can place each light above the plant. Do I need to worry about the CMH loosing intensity over 3-4feet wide ? I cannot go to a large CMH due to heat concern in my grow space, that is a whole other story

CMH is 315w and covers a 3x3' square space with 35w/sq ft.

There are 150w CMH bulbs with screw base. Search for Sun Pulse. I don't know anything about these (what kind of ballast or reflector they use, socket, etc.). If they're as effective as the higher-watt CMH, then 150w should cover 4.3 sq ft. About a 2x2 space.

Get one of those and one LED? See how they compare?

Maybe things have improved with LED in the past 3-4 years since I used it (and stayed aware of things). Back then, I would not expect 100w (actual) LED to cover much space (nor penetrate much; nor produce frosty buds). Which lights are you considering buying?

If the frosty part isn't a concern for you, you can sidelight plants with ordinary household LED lightbulbs. If the 100w fixtures don't cut it, it's not hard to throw more light around the plants to make up the difference (9w at a time).

That's what I always saw. Most lights didn't cover the area advertised. Someone would buy a 100w (actual) thinking it should cover a 2x2 space. But, it only covered half that amount. They ended up running 40-50w/sq ft. At which point... why not run T5HO at 40-45, or CMH at 35?

You're coming at it from "100w should be enough for 16" centers." Maybe things have changed. I hope they have. But... from my not-so recent experience, I think you're assuming too much about those lights.

If you want to know more about the household-lightbulb topic, I can explain more.

You're doing shorter scrog growing. Maybe T5HO would be the answer.

What will be the dimension of the screen? The grow space? If it's going to be 3x3, that's perfect for 315w CMH. Whatever you're worried about with the light losing intensity is not an issue. My only concern would be if the grow space is 16" by 32". That's not optimal for a 315 LEC.

[az2000]

FYI: I've been digging deeper into that Sun Pulse CMH 150w. Apparently it's intended to be used in a Summit Lighting "Summit 150" fixture which has an integrated ballast. The product page says it's intended to replace a T5 (fluorescent?) fixture with half the watts.

I've googled and can't find anyone growing with one. I'm curious about getting one to see how it might work in a short grow space (if it can be close to the canopy).

I wouldn't recommend you get one. It could be junk. I just wanted to fill in the blanks about it.

[Gjohnstone]

Thanks for everyone’s input. When I am talking about 100w COBs I am talking about something like what I attached.

[Canuck147]

Good idea - keep in mind you need it 36 inches above the plant at start and once your past the seedling stage you pretty much set it 24 inches above the plant for the rest of it's cycles.

[Gjohnstone]

Sorry, good idea and the height suggestion on the cob or CMH. Thanks