Good read on UVB

Busting common myths about cannabis and UV

I’ve been working with UV over 27 years, with half of that being directly with cannabis growers, including some rather famous ones you’ve heard of and perhaps have bought a book or two from. We have a network of hundreds of growers, dozens of testers, and a couple of different labs we work from. I don’t know much, but I know UV.

I get on Facebook and other social media and I find that most people talking about UV simply have bad information. They just don’t understand it. Some of them are convinced they do, and a rare few think they are experts because they have a year’s experience with it. Most people just read bad information that keeps getting passed around as if it is gospel, when in fact, the information is false. This page is designed to bust some of those myths, from someone who actually is an expert on UV. I try to keep it light, and just deal with one issue at a time.

You only need UV light for the last 2/3/4 weeks of flowering

Not exactly. You can use UVB (UVA is much less helpful in this situation) only in the last few weeks and yes, it will be better than if you didn’t, but you are missing out on the true potential of UVA/B. In the wild, plants don’t get UV just in the last 2 to 4 weeks. In fact, they get much LESS UV during the last month of flowering than they do during veg simply because of the angle of the sun. Plants will absolutely produce more trichomes, more THC if you use a proper UVB bulb during the entire flowering season. In fact, most larger, successful growers will run them an hour a day during the last half of veg to harden them, and to kill off any risk of powdery mildew.

I don’t need UV, my LED system (or CMH or MH) already has it

Your LED has 365nm and higher, not UVB. Also, it has a very low amount of UVA at 365nm. I’m sure it is helpful, but 365nm will NOT increase trichome production. Only 280nm-320nm does that, and 280-290nm in particular. This is why our Flower Power does a better job than our Universal UV. The Universal is similar to other lamps on the market and does a good job but doesn’t produce 280-290nm. The Flower Power does product 280nm+ and smokes everything else because of it. So while your LEDs have a little UVA, they are missing out of the most important part of the UV spectrum; high frequency UVB, and THAT is where trichrome production is triggered.

I can’t run your UV bulbs, I’m using LED / HPS / MH / whatever

You can run Flower Power bulbs with any general lighting. They won’t interfere because they produce virtually zero visible light. They pick up where your general lighting leaves off, around 400nm. No matter what general lighting you use, they will work and do the same great job.

All you need is a reptile bulb

Technically, you don’t NEED anything, but a reptile bulb is pretty mild and won’t get dramatic results. The problem is that the majority of the output from a reptile bulb is actually NOT ultraviolet, but it is visible light. This doesn’t help you, and in fact, interferes with your color temperature if you run a tight setup. To compare, a Flower Power bulb is going to be about 20 times stronger in he UVB region. This is why you only use them for 2 hours a day, and why they work. To get the most of the plant, you have to hammer it for a short while, then let it rest for the bulk of the day. Otherwise, you aren’t really stressing it, and you won’t get the high trichome production.

All UVB lamps are pretty much the same

Very wrong for a variety of reasons. For starters, UVB isn’t a singular thing. It is a range of colors that span 280nm to 320nm. Virtually all UVB bulbs only produce only the lower energy portion of that spectrum, 300-320nm. The Flower Power is the exception, because it uses a patented glass. The higher bands from 280-290nm in particular are exponentially more powerful and where you get a real defense reaction from the plant.

As long as you give it some kind of UVB, you are going to get the same results

Basic plant biology says otherwise. The protein that tells cannabis (and other plants) that they are in a high UVB environment is called UVR8. Triggering this protein is what makes the plant go into overdrive and produce tons of extra trichomes. The only way this is triggered is by exposure to 280-290nm. The overwhelming majority of UVB lamps do not produce this range. The Flower Power does.

UV will damage the plants and give you cancer

I get this one every now and then. Plants evolved in the sun, where there is UV, so did humans. The key is using the right UV, for the right amount of time, and not overexposing the plants (or yourself). It’s simply not worth debating, the science is utterly clear that humans and plants both benefit from moderate amounts of UV.

UV will interfere with my lights

Any good, pure UV light (meaning it has zero visible phosphors) will not. This includes the Universal UV, the Super B and the Flower Power. They produce almost zero visible light. In fact, it’s kind of hard to tell if they are on unless you look at them directly. Since virtually all their energy is 400nm and below, they will not interfere with your visible light, which is 400nm to 700nm, and obviously they won’t interfere with any infrared you have. Lights that mix UV and visible light (reptile lights, for example), WILL change the color temperature in the room.

I tried reptile lights, but they didn’t kill powdery mildew, so UV won’t kill PM

Illogical leap of logic. Reptile lights are weak, on purpose. Flower Power bulbs are 20x stronger in the UVB region, and many times stronger in the UVA. Both high UVA and UVB help kill powdery mildew. We have hundreds of users that use them solely for that purpose. The key is adding UV before you have a huge problem. Used regularly, you will find PM is a thing of the past. The extreme intensity is why they work. For treating PM, you need to run two hours continuously per day, no breaking up the time. Hammer it hard and heavy and in all but the most messed up situations, it will kill it.

You don’t need UVB to grow great cannabis

True and false. Obviously you can grow great cannabis without adding UVB, underground growers have done it for years. But if you take that same grow situation and add the right amount of Flower Power, you are guaranteed to increase THC by at least 15% (for example, going from 17% to almost 20%) and many experienced growers are getting 25% (going from 22% to 29%) or even more. Some growers are reporting total THC of 30-35%. It is very difficult to achieve those numbers without very good UVB.

Adding UVB will reduce your yields

True and false. If you use Flower Power for two hours a day, you will find your yields are exactly the same as without them, except a larger ratio will be THC. If you work your plants up to 4 or 5 hours a day (most growers don’t try this), then yes, it start cutting yields by 5-15% but it boosts THC dramatically. For 99% of our customers, we recommend you stick with the 2 hours a day, get the same yields, get more THC, and keep it simple.

It’s too expensive

It isn’t free, but do the math: A $40 bulb will at LEAST 4 plants for 3 flowering seasons. That is a minimum. Lets keep the math simple: That means 4x3=12 plants will benefit from that bulb. Cost per plant is $3.33. If it increases just a MINIMUM of 15% more THC, you’ve paid for the bulb before the first harvest. If you get the average gain, 20% higher THC (really it is 25%, but let’s err on the safe side), and you get 12oz from each plant (a low minimum), that means the 144oz that you harvest will go from 20% THC to 24% THC. Or from 25% THC to 30% THC. Guaranteed. Is that worth $3.33 a plant? Plus, don’t forget, you’re also getting the mold and mildew suppression and insect suppression. In reality, Flower Power are very, very inexpensive. Not using them is expensive.

Any UVB is better than none

Actually, this one is true. Even a cheap UVB bulb is better than no UVB. That said, for a little more than a cheap UVB bulb, you can have the best UVB around, and since Flower Power last twice as long, they really aren’t more expensive. So use what you have, but make room to upgrade later if you really want top shelf results.

Questions based on real questions over the years. Answers by Dennis Brown


This is a good read.


i have been growing cannabis indoors since 2013 for the first 2 years i grew using hortilux HPS, my weed was dense frosty nugs but the quality was always lacking. after i started adding 10k solis tek MH vertical bare bulbs my end quality skyrocketed!.

because of your article i made a account on these forums.

i appreciate you spreading this information around.

I am in the process of replacing my LED light with a 315w 10k CMH i dont care if i get low yields from a bulb that produces 70 lumens per watt as long as my THC and terpenes kick like a mule!

i understand that most of the UV emitted by a 10k CMH is UVA im hoping it emits enough UVB to make a difference(and i hope it emits a little bit of UVC)

i have been flowering with 10k solis tek metal halides for a very long time and they have given me low yields but amazing end quality! i hope the 10k CMH does the same. and when i would grow with 10k solis tek metal halides i never had a problem with powdery mildew or mold or bud rot i mean i never had one issue, so i hope that i get the same results with a 10k CMH :frowning: fingers crossed.

i will also look into the flower power bulbs maybe i can add one next to my LED light but i honestly need the heat generated by a CMH this time of year so i will probably rock a 10K CMH instead of the flower power.


Not my article I just thought it was a good read and thought I should share