Warning! Not all LEDs alike

^This! If it ain’t broke, don’t fix it.

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You looking for 50+ watts per sq.ft

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For MH/HPS yes - but according to the peeps in Bergman’s Lab they say minimum for LED is 25w (true) per sq. foot and ideally 35w per sq. ft. Here is part of a post from @MacGyverStoner on this subject:

At a bare minimum you need 25 watts of actual LED power per square foot of growing space for cannabis, and many recommend actually 35 actual watts per square foot for LEDs.

So let’s look at these numbers and keep in mind a 3’ x 3’ area is 9 square feet:

90 watts divided by 25 watts/sq ft = 3.6 square feet
90 divided by 35 = 2.57 square feet

110 watts divided by 25 watts/sq ft = 4.4 square feet
110 divided by 35 = 3.14 square feet

120 watts divided by 25 watts/sq ft = 4.8 square feet
120 divided by 35 = 3.43 square feet

I wish you the best of luck with that. Tried it myself, not so great. Need 50+ tru watts 75 -80 is were I’m at ,and it’s better then ok but not awesome.

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I’m a total newb so I’m just regurgitating what people smarter than me have said. :slight_smile: I think I will end up following your lead at some point and getting to at least the 50w/sq. ft number. Right now I’m just happy if I can keep the plants alive long enough to harvest.

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@Bogleg and @Wishingilivedina420state you guys are both correct. The 50 watts per foot squared is kind of an old school number, but has its place. When sizing led for grow it really becomes necessary to account for the efficiency of led you’re going to use. Running 25-30 watts of something like a high intensity modern cob led will produce a much higher ppfd (photosynthetic photon Flux density) than say 25-30 watts of epistar or equivalent discrete diodes. So you can’t exactly compare the two on an apples for apples level.

So to say that you need 50 watts per square foot isn’t exactly true, but only needing 25-35 watts doesn’t tell the whole story either. If you’re going with led, look for the par readings usually shown in some sort of map in ųmols. Also, pay close attention to at what height the advertised readings are taken. Law of inverse square will tell you all about how light intensity is changed by height. If you get to higher end lights, the manufacturers will usually tell you exactly what the ppfd is and the electrical efficiency of the fixture as well. For example the latest numbers I’ve seen on de gavita 1000w are around 800ppfd in 4x4 with 1.7 ųmol/joule. It doesn’t take 1000 watts of cobs or quantam boards to hit those numbers. But there’s not a chance hell a fixture claiming to be a 1000w replacement for under $200 is going to match up.

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I just need to win the lottery or sell my car or something so I can afford a couple of BDL 400w lights and a second tent.

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What is bdl 400 @Bogleg ? Black dog?

Yessir. That’s the one.

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They’re not bad, but if you compare them to more of the commercially designed lights, you’ll find better performance for less money.

They don’t give a very detailed description of their spectrum either. If you use their tool and layer with light visible to the human eye it appears that flowering peak is in the near infrared area. At least the chart shows the red peak as “not visible to human eye”. That should definitely raise some questions! Almost every study I’ve seen suggests peak absorbtion in the 630-660 nm range, and both of those wavelengths are clearly and easily visible to the human eye. I suspect it’s just not a very chart, which would lead me to wonder what the provided spectrum actually is.

If you buy into the addition of the additional wavelengths outside of the par spectrum, then you could justify paying a little more. But that’s a whole different story. They’re providing down to 365nm which is still uva. All of the scientific data I’ve seen shows uvb to provide benefits. As far as ir goes, it’s kind of the same story. While ir or near ir has benefits, it’s most beneficial in the absence of red or in short periods right at lights on and lights off. At any rate, uva and ir stars can be purchased for literally a few bucks each. Even if you were a true believer that their light spectrum was that much better… buy a light that produces more par for half the price, and throw a couple of uva and ir diodes on it for $40-50.

Just my opinion, so take that for what it is. Like I said in the beginning, it’s not a bad light. It’s just very expensive in the ųmol per dollar category.

Please tell me that you have a book so I can buy it.

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No book sorry. But the info is all out there. If you’re wanting to learn about the light spectrums, look for info on the McCree action spectrum. It’s still probably the most thoroughly used and referenced study. Also, @Niala has some NASA information too, I’m sure he will share. I would definitely start there, it will definitely help with understanding the differences in one light to another.

After that, it’s really about efficacy and efficiency with led"s. They usually correlate to each other, and are the reason one diode you can buy for a quarter and a different one will cost $5.

How about 90w squareFeet?

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I am not highly experienced, so take this for what it is worth.

From what I have read and understand, 90w a square foot is probably overkill. Unless you provide enough nutrients and CO2, the plant will not be able to use all the light. Plus, you may have light burn and heat issues.

Of course much of this depends on the environment in which you grow. If you have lots of space and can provide all the ingredients, you should get an excellent result.

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90w sq ft sounds great :+1:, gotta agree with @Medforme said it better then I could have @beginner2d
With that said I think I’m around 75-80 and it took a little bit to get it dialed in but I think I’m there now.

I think co2 is not a problem. Fresh air come passive way in sprouting and when they become to puberty i get my 10 air intake going.Nothing fancy, ithink they can handle. Nutrients:start bio degredable pot (good soil, and then transplant another good soil, and i think autos dont need so much nutes. Or can light power per sq/feet is actually thing and i must nute them harder with brighter light? you really think i do lightburns for that outcomewith right heights? Veg i go 1vipraspectra600w only veg switch and dont burn them when youngsters. And over time i add second veg switch other vipra. Then both lights on when they preflower.(autos) and i dont know… Is this both switch setUp must go to the end or somewhere i must switch only bloom ??

Then i must hack my growroom bigger :wink:

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That’s a good idea :bulb: too…

Hopefully you are calculating your 90 watts per square foot off of the imaginary equivalent wattage claimed for your light. Even budget led fixture par levels will exceed ambient co2 availability at that rate. Doesn’t necessarily mean it will hurt your plants, but the excess energy being consumed won’t yield anymore either.

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“imaginary equivalent wattage claimed for your light”.
That means? 600w. actual out of wall 272 .ok maybe 250 real-maybe less ,but is that underpowered you think? Ill have autos under it ,not photos. Photos i think with tehniques uses can handle only one girl.