We live in an odd time, one where cannabis is legal in some states, legal for medical use in others, CBD is sort of legal in yet others, and it is completely illegal in yet more, all while the Federal government has yet to deschedule anything. This is complicated by the fact that we aren't a blog, we are a company that sells products. Overwhelmingly, those products are for UV curing, but some go to cannabis growers in states where it is legal to grow. With that in mind, please read this disclaimer: The information presented herein is proved for educational use only, and is protected by the 1st Amendment of the US Constitution. We can not knowingly sell any product that is intended to facilitate a crime in your state or country. If you tell us that you want to buy lamps for growing cannabis (marijuana) in a state and it is illegal in that state, we can't sell it to you. If you don't say, we don't assume you are a criminal, and just ship the item. Ok, now on to the info.

Plant stressing theory
The first thing to understand is that there is a reason why people are using UV lights for growing, it isn't hype, it is scientific fact. When people started growing indoors, they found their plants were more potent, and didn't give UV a second thought. If it isn't broke, why fix it? Some may have thought that the zero to low UV environment was good for the plant. After all, the government (and some in the medical community) has been brainwashing the public into thinking that all UV is bad and should be avoided. Meanwhile, since that campaign started, now most of the US has a vitamin D deficiency (easily solved with a few minutes of sun every day) and cannabis growers have been missing out on something that boosts the potential of their plants: Ultraviolet.

You have to understand that humans and plants alike evolved with UV being ever present, and have evolved techniques to deal with it. For humans, UVB causes our skin to produce melanin and UVA causes that melanin to react with oxygen (to oxidize) and turn brown. This brown skin color protects our skin from damage from UV, so we basically create our own sunblock. As long as we don't overdo it and overexpose all the time, our built-in system of self-protection works quite well, and as a bonus, it creates vitamin D in the process, a vitamin that we don't really get anywhere else in nature except in mushrooms or artificially introduced, such as fortified milk.

Plants have different strategies, and react differently to UV exposure. This is most obvious in plants that have trichomes, which little hair like structures that produce resins. The most obvious plants that have trichomes are members of the Nightshade family (Solanaceae), such as tomatoes, peppers and oddly enough, tobacco. Another plant with trichomes is cannabis.

Tomatoes will produce a fleshier skin and fill it with flavonoids. This is a good thing, and explains why tomatoes grown in the open taste better than tomatoes grown in a greenhouse, as greenhouse glass filters out most of the UV. Cannabis is a bit different because the trichomes are directly on and around the flower itself, and they react strongly to UV and try to protect the fruit (seeds) by oozing a UV resistant coating on the flower to insure the seeds are not damaged by ultraviolet. Of course, they do this even if there aren't any seeds yet. The resin they produce that acts as a sunblock is tetrahydrocannabinol (aka: THC). THC has a high ability to absorb UVB, so the more UVB there is, the more THC that the flower will produce as a reaction. Growing looking to maximize cannabidiol (CBD) would minimize UV exposure, to inhibit the need of the plant to protect itself. Growers looking to maximize THC want to add UV. This may explain why so many of the CBD only strains are grow in greenhouses, as greenhouse glass (and most glass in general) blocks UVB, thus the plant doesn't waste energy producing THC.

Indoor growers wanting to maximize THC can accomplish this by supplemental lighting that has the proper blend of UV. You can use a little or a lot, with better results as you add UV, to a point. Keep in mind that you are changing the activity when you force it to produce THC, so the net result will be slightly smaller flower buds, but significantly more potent in terms of THC. A plant can only expend so much energy, by using UVB lights, you are taking away the energy it would spend in one area (growing a bit more, growing larger flowers) and forcing it to put that energy somewhere else, ie: THC production. The net energy spent by the plant is the same, you are just forcing it to produce clear resin instead of green leaves.

How much more potent depends on the strain and how you use the light, there is no single figure for this. I've seen people using reptile lights to squeeze another 3% THC, and I know of people claiming 20-35% using one of our lamps (actual lab results, not guessing). The main focus has been about UVB, but UVA also plays a role, just one that we haven't fully studied enough to have firm science on. Regardless, any UVBA/B lamp will help some, and the right one will make a huge difference in resin production. There are tons of small studies on this, all that back this up. Anyone that says otherwise simply didn't do it right. That is ok, it takes some experimenting, but trust me, it will work.

Ok, but how do I do it?
Every situation is different, so you have to dial in the proper mechanism yourself, but there are some good guidelines to get you started. For starters, the best lamp to use a 4 foot lamp, like our Universal UV or SG-4 bulbs. You can buy 32 to 40 watt single or double lamp fixtures at any hardware store, so it is cheap to maintain and setup. The 4 foot length is also easy to work with. Essentially, they are the same format (size) as an office light, although they are very different otherwise. We use a specialized lamp end (cathode/anode), different gasses and pressures, different glass and obviously different phosphors. One for every 2 to 4 plants is best. If your plants are extraordinary compact and you want to run the lights farther away (but for much more extended periods of time) you might get away with one light per 8 plants, but this is trickier. You will need a different timer for them, as distance will change the exposure schedule. You start out with an hour or two, and work your way up. Typically, you only need to use them for the flowering stage, but some people use them after the plants are a month old for the purpose of controlling mildew and mold, which do not like ultraviolet at all. This use has lots of theory and very little testing in the field, so your mileage may vary here.

The key is to have the lights covering as much of the plant as is reasonable. Keep in mind that humans and plants act differently to UV. Humans only tan where our skin is directly exposed, which is how we get tan lines. In theory, if you cover much of the plant with UV, all of the plant should react as if it received UV, although it is still better to insure all the flowers get at least some UV. This is based on the science of how plants react during fires, whereby one part of the tree is exposed to smoke, and all the tree sends chemical signals to other trees. Plants react to stimuli more broadly than humans. Still, you need to expose a fair amount of the plant, particularly if you are testing for mold/mildew protection. More is always better but for normal use, if you can get 50% of the plant bathed in UVB, you are probably ok; covering the entire plant is better.

Just as with humans, your goal is to cause a small amount of damage to the plant. It doesn't need to be much, just barely enough to see, so the plant knows it has been damaged. This is what causes it to react by producing extra sunscreen (THC). Once you are at that point, dial back the UV a little so you don't do more than just a tiny amount of damage. It helps to note that the lamps we sell for growers (of cannabis or any other plant) contain more UVA than UVB. UVB doesn't penetrate very deeply; UVA penetrates more but does very little damage. We blend the lamps to have both because the sun has both, so we are trying to recreate the UV they get outdoors, and you decide the level using the timer. In the case of the Universal UV lamp, it is tailored to deliver twice the UVB versus UVA that a plant would get if grown in the southern USA / northern Mexico, around 10% UVB and 90% UVA, where as the sun is typically 5/95 there. This is the extra UVB boost you need for maximum results, while still delivering the full spectrum of UV, matching what the plant would see in the wild. Note that we don't build wimpy lamps: these are very strong lamps, it is easy to overdo it. The SG-4 lamps are different, and while they have a lower relative UVB output, their total UV output is much higher.

How many bulbs do I need?
That depends on how you use them, how you power and mount them and how much UVB you are trying to introduce to the plants. Let's assume we are talking about the Universal UV lamp, and that you are going to power them with generic, single bulb, 32 watt light fixtures (F32). This is what I actually recommend, as the lamps will put out a reasonable amount of UV at 32 watts and have a longer than average light span, PLUS...it is cheaper. You can buy the fixtures from Lowes or Home Depot for $20-$25 each, and if you ever need to replace one, you just go buy another. It is even cheaper to use the two bulb fixtures, but you need to put any old office bulb in the other slot to get them to light. (Two Universals in the same fixture is probably a bit intense) You have less maintenance this way. You can also wall mount or chain mount these fixtures. Keep in mind, the white mylar or paint will NOT reflect the UV, only the reflect that is built inside the lamp does. UV is really hard to reflect...

Again, you are probably looking at one lamp/fixture for every one to two plants, depending on the strain you are growing, and how close you want to get. Obviously sativa plants are larger and bushier than indica plants, so it takes more points of light to cover them. A room with 100 plants would need 40-60 lamps at a bare minimum. Keep in mind, the goal isn't to cover every square inch of the plant, just to cover most of it of it with UV and rotate when you can. The farther the lamp is from the plants, the more plants it covers, but the weaker the UV will be.

How much weaker? The inverse square law applies here. It says that if you double the distance from the light to the plant, you reduce the UV power by 75%. The power drop is exponential with distance, so closer is better. This is because it isn't just casting light in one dimension, but two: width and length, or put another way, the X and Y axis. For those of you are that are nerdy, here is a diagram that explains this:

Per Wikipedia: "...intensity is inversely proportional to the square of the distance from the source of that physical quantity." Because they light spreads in both the X and Y axis, the amount that reaches the plant isn't reduced in a linear manner, and instead is reduced exponentially. Put another way, if you double the distance, the power goes down by 75%. If you cut the distance in half, the power goes up 400%.

Just before the plants start flowering, you begin using the UV lights, starting with 1 hour and working your way up. How much depends on how far away they are. 1 foot or less or so is fine, these lights are designed to do just that. Getting the sides of the plants is good if you can hang and angle them slightly. Again, you are trying to cause (or almost cause) a tiny bit of damage, but it may take two or three days for the damage to show up, so you need to be careful as you dial this up to several hours per day.

How long will the lamps last?
You can probably get 2 grow cycles if you use them during flowering only (twice that for the SG-1 or SG-4 lamps), 1 if you use them for growth and flowering (mold reduction). Some try to get 3 seasons with mixed results. but we don't recommend it because the output drops off too much. If you consider the return, you won't want to risk it once you've tried it, the lamps pay for themselves 10x to 20x over. The lights will look the same on day 1 as day 120 to you eyes, so you just need to mark the date on them, or take notes. Short on/off cycles kill lamp life, whereas long cycles can give you more. You could probably try to squeeze a 3rd season but only as the "spare" bulb in the fixture, next to a new bulb. They will still light up well after the UV has diminished. Hard core growers looking at maximum control may change them every season, and maybe rotate the older bulbs back for growing plants, as mold control. They will still be 70-80% effective at that point, which is good enough for that purpose.