UVB is supposed to enhance trichome production and also raise THC levels. It needs to be added because it is not available with regular lighting used to grow weed. Metal halide has some but the glass does not allow it through.
UV light is used in hospitals to keep things sterile and it can help control mold in the grow room too. Imagine no more powdery mildew or bud rot! You can use UVB bulbs throughout the entire flower cycle but for shorter exposure times. It is reported to produce shorter stockier plants , improve bud density and produce healthier greener plants.
Most reptile bulbs provide UVA light which is helpful for plant growth but have very low levels of UVB light which is what boosts trichomes and THC levels.
Our atmosphere filters out most of this spectrum but UVB light is at higher levels as altitude increases which may explain why most premier growing areas are at higher altitudes.
Because most of us are growing indoors our plants do not get the UV light the sun provides so we need to add it with UV bulbs. This may explain partly why plants tend to grow better outdoors.
Solacure has been making UVB bulbs for years and I have heard they make the best. But before I spent a lot of money on bulbs I wanted to test them out. The Reptisun 10.0 UVB bulb does not make as much UVB as the Solacure bulbs.
But it produces more than anything else in the reptile bulb class. The Solacure bulbs would toast your lizard so it seemed if the Reptisun 10.0 UVB bulbs worked the more powerful ones would be worth the investment. Here is my test video:
UVB TEST WITH REPTISUN 10.0 UVB BULB
Here are some pictures taken on day 59 of my current grow. There has definitely been a change in these plants even with a weaker UVB bulb and I think I will be using the more expensive bulbs in the future.
The fade on these girls has accelerated. After a few days some fans are turning crispy. Trichome production seems better and some plants seem to be producing more white hairs which is probably a reaction to the light. Plants in the pics are mostly Gelato #33 and some Grim Bastard OG
Explaining UV and Cannabis
Here is part of an article explaining UV for cannabis lighting:
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 “burgundy” 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. http://www.solacure.com/exuvandca.html
ReptiSun 10.0 UVB Review
So here’s my take. The Reptisun 10.0 UVB bulb does definitely have an effect on cannabis plants. I dont test so I can not say if UVB raises THC levels. I can say that I see more trichomes or at least more developed ones. I definitely see the effect of the light on the leaves. In fact I will probably be harvesting a few days earlier.
I consider buying these bulbs a good investment and that the test proved successful. I have seen enough that I plan on buying the Solacure UVB bulbs in the future. I would recommend either product but if you are not sure or dont have a lot to spend try the Reptisun 10.0 UVB bulbs.
A lot of reviews on UVB light for weed are mixed. Some say it works, some say it doesn’t. Based on what I am seeing I feel the failure to see results is from lights without enough UVB to make a difference. If I am seeing results now I can hardly wait to see what the Solacure bulbs can do.
If you are looking for a high quality white LED that really can replace a 1000w HPS then you want the HLG 550 V2.
I was running all COBs and replaced them with a 550 and as good as Cree COBs are, there is just no comparison.
Here is a UVB test in another grow.
Experimental Grow Closet #2 Low Pressure Aeroponics | UVB Bulb Test