Monthly Archives: February 2016

Cannabis and UVB

By Bokske - Own work, CC BY-SA 3.0,
Cluster of female cannabis flowers
You’ve probably found yourself here because you’ve heard that ultraviolet might increase the potency of cannabis. You might have also have heard some people say it isn’t true, and you are curious as to whether or not it really does. The purpose of this article is provide you some information, and some citations demonstrating the concept and why it really works and works extremely well if you do it right. The science behind the idea dates back to the 1980s and perhaps earlier, so this is a summary of that research. Much of this might be a bit of an oversimplification, but the goal is to give you an overview of why proper UV works, it isn’t to be a science class.

When we talk about ultraviolet and increased potency in cannabis, we are singularly talking about THC (Tetrahydrocannabinol) production. The effect of UV on the other 84+ cannabinoids isn’t fully known, nor has it been studied in detail. One would assume that if you increase the amount of THC, you are probably lowerin the amount of other cannabinoids (in particular, CBD or Cannabidiol), but this is just conjecture and the adecdotal evidence is conficting. Growers who are trying to produce marijuana that is moderate or low in THC but high in CBD would actually want to avoid ultraviolet, which explains why it is always grown in greenhouses (whose glass filters out all of the UVB and most of the UVA). Most growers, however, are wanting to grow cannabis that is high in THC, whether it is for medicinal use or recreational use. This article applies to them.

Understanding the plant

Most plants on the planet have both male and female flowers, making them hermaphrodites (monoecious). Cannabis is one of the rare plants that has individual genders, both male and female plants (dioecious[4]), although some plants will have both male and female flowers. The female is the grower’s target, and growing largest and most potent flowers (buds) is the goal. To this end, all males are removed, to prevent the female from going to seed. The key is, no one has told the female that she will never be pollenated. As far as the female plant is concerned, her flowers/buds are the bed for her children (seeds) and she simply hasn’t been pollenated yet. Her seeds are the only way she can reproduce, and reproducing is the primary purpose of every plant. As such, she will protect that flower as if it has her children in it, even before it does. Like most plants, cannabis has built in protection mechanisms to guarantee the next generations, which takes us to THC.

That THC is psychoactive is perhaps an accident. This quality hasn’t necessarily benefitted the plant, except those qualities has insured that man has cultivated the plant for thousands of years. THC has a biological role for the female plant that is critical for you to understand: THC has very high UVB absorption rates, meaning it is like sunblock for the plant.[1][2][3]


The ultraviolet spectrum is broken into three bands. They are actually “colors”, we just can’t see them. Like colors, there is a range within each color. This is how “pink” and “burgandy” are both types of red, just different parts of the red spectrum. The same for ultraviolet. If you look at a rainbow, you see the colors go from deep red (wavelength of 700nm) all the way to violet (400nm). The next color is UVA (320nm-400nm), then UVB (280nm-320nm) and finally UVC (10nm-280nm or 100nm-280nm, depending on who you ask). UVC is used for water purification and such because it kills organisms. It can also give you a flash burn in a few seconds, so fortunately, the atmosphere filters out almost all of it. When a plant is outside, they get a fair amount of UVA and UVB, typically in a ratio that is around 5% UVB and 95% UVA. They have evolved over millenia to adapt to this and survive. In the case of cannabis, the plant developed THC to protect the next generation. The more UV it is exposed to (to a point), the more THC it will produce.

When we moved growing cannabis to the indoors and in greenhouses, we did remove a lot of dangers to the plant: wind, soaking rains, animals, most insects and more. This increased the yield by 100% or more. The problem is that high pressure sodium (HPS) has zero UV of any kind. Metal halides have .5%, which is a negligible amount. The plants grow well, they are large, thick, robust and even potent, but they are far below their potential because we made their environment TOO perfect. Without the stress of UV, they have no need to shift resources into producing high amounts of THC. Instead, they produce a default amount, programmed by their DNA.

The process

In order to increase the THC, you need to understand that plants aren’t lazy. They spend all their time doing something: growing tall, growing buds, creating THC, moving nutrients around and such. When you introduce the proper spectrum of UV to the plant, you are forcing it to shift its resources into protecting itself. It will spend a little less time growing sun leaves, sugar leaves and even the buds will be more dense and just a hair smaller, but it will produce a lot more THC. Since THC is the ultimate goal, the market potential is significantly higher for plants grown with proper UV. It short, it makes you a LOT more money.

Using proper UV can cost you $5 to $10 per plant when you average out the cost of lights and fixtures. It is very cheap. Most people are able to get increases of 20% THC the first time they use it. Most experienced growers are getting over 30% more THC than with clones that aren’t getting UV. These aren’t guesses, our dispensory and grower customers report back to us with actual lab results, using actual control growing methods. Anyone who tells you they didn’t get more THC is probably using a reptile light or some similar underpowered UV source. Just as you can’t use regular screw in light bulbs to grow robust plants, you can’t expect high THC returns with weak UV sources. Ironically, the bad UV lights cost about the same as the good ones, it is just a matter of using the right lamps, the right way. And it is pretty easy IF you know how. With our standard 4 foot bulbs (Universal UV and the SG-1-40) you will use four bulbs for every 1000w (or equivalent) hood you have. Newer lamps in testing will cut that in half.

Proper usage

The key is giving the plants as much or more UV, in the right spectrum, than they would get if they were outdoors. In fact, you want to give them as much as they can take without being damaged. This means light on each and every bud, at least every other day. Typically, you would run the UV lights for your full light cycle, around 12 hours, as soon as you go into flowering mode or even earlier.

It takes more than just random UVB. We have found certain frequencies of UVB make the plant react more vigorously than others. We have reason to believe that UVA is also beneficial. While it doesn’t stimulate THC production, it penetrates much more deeply than UVB and may stimulated trichome production, which makes THC possible. This is why we have UVB lights with multiple “soft” peaks at the right frequencies, as well as strong UVA output in exactly the same part of the spectrum that the sun is strongest at. This gives you a sun-like glass tube that you control.


So does it work? Unquestionably it works as long as you use the right power level and right frequencies, and the pay off is often 100x the investment. This is huge. This is also why many growers are using our lamps, and why many growers don’t let anyone know that they are using our lamps: They don’t want anyone to know their secret, why they get the big bucks, why they have the best product. Of course, it still takes good light, good water and soil, good care and air, and proper technique, but UV light is just as important as those other things if you are after premium results.


1) * Pate, David W. (1983). “Possible role of ultraviolet radiation in evolution of Cannabis chemotypes”. Economic Botany 37 (4): 396–405. doi:10.1007/BF02904200
2) * Lydon, John; Teramura, Alan H. (1987). “Photochemical decomposition of cannabidiol in its resin base”. Phytochemistry 26 (4): 1216–1217. doi:10.1016/S0031-9422(00)82388-2
3) * Lydon J, Teramura AH, Coffman CB (1987). “UV-B radiation effects on photosynthesis, growth and cannabinoid production of two Cannabis sativa chemotypes”. Photochemistry and Photobiology 46 (2): 201–206. doi:10.1111/j.1751-1097.1987.tb04757.x. PMID 3628508
4) * Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9
5) *
*) Help locating some sources came from

Dennis Brown

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