Scientific Study – The Effect of UVB on Cannabinoid Production in Cannabis Sativa

It has been widely suggested that UVB can increase the production of THC in Cannabis Sativa.  But it turns out, the University of Maryland, in conjunction with the Southern Weed Science Laboratory (I kid you not) in Mississippi, (could have guessed that one and they are clearly aligned with the University of Miss which was the ONLY University that was allowed to do research with cannabis since it became illegal in 1986!)

The report is a rich buffet of tech speak and I will not bore you with it, but the bottom line is this:

They tested two strains of Cannabis Sativa, one “drug” strain, and one “Fiber” strain (i.e. hemp).

They exposed these plants to 2 levels of UVB,  roughly the UVB exposure of full sun at the equator, and 1/2 that amount, and none. And they ran the UVB for 3 hours

They tested for both THC content AND CBD.

The results were quite amazing:

Growth (as measured from Co2 absorption) was not affected whatsoever.

CBD levels in the flower resins were unaffected by UVB.

THC levels in the flower resins increased from 25% baseline with no exposure to to 32% in equatorial sun UVB!  They also suggested in the report that it appears that the THC acts as a sunscreen for the Seeds.   —  Silas agrees!

This aligns with with the feedback California LightWorks (CLW) has related to me from their growers who have actual THC lab test results averaging around 2-3% higher THC levels, i.e. the bud starts at 22% THC without UVB and goes up to 25% when running UVB.  Each CLW fixture has 30 WATTS of UV, and can deliver as high as 20-30% of Sunlight UVB depending on proximity from the canopy and how many UVB lamps are used per sq meter of canopy.

This is one reason that when I switched to LEDs a year ago, I chose the California LightWorks SS440’s (2 per 4×4 of canopy).  No one else uses mercury vapor lamps for UV , and with 30 YEARS of Lighting design experience I can assure you that Mercury Vapor lamps are the ONLY source that will get you anywhere near sunlight levels of UVB OR UVA.

All the other LED grow light manufacturers that claim to provide UV, provide ONLY UVA,  and ONLY minuscule amounts — I am willing to bet most of them just put 1 (yes ONE)  1-watt UV LED in there,  just so they can SAY it has UV (none publish the UV wattage of course) —  but I can guarantee you they deliver less than 5% of the levels (if any) that the CLW fixtures provide if they use UV LEDs.   Just remember,  Silas got’s your back when it comes to phony claims.

So if you are looking to use UV to increase your THC levels, the California LightWorks product is (so far) the only legitimate option I have been able to find. As I understand it, they are also making a new line coming out in February that will have independent UVB fixtures so you can add as much UVB as you want!!! I think I will get a few more…

Nothing like REAL science that supports the mythology.

To those who grow WE SALUTE YOU!!!


Click on the link below to read the actual report (but don’t forget your “trying way to hard to sound like a scientist” decoder ring):

UVB Effects on Photosynthesis, Growth, and Cannabinoid Production in Cannabis Sativa


2 thoughts on “Scientific Study – The Effect of UVB on Cannabinoid Production in Cannabis Sativa”

  1. I recently ran a side-by-side test using a UV heavy finishing bulb.
    For my control I ran the Solistek HPS DE for the full flowering cycle (9 weeks) with 3 strains.
    For the test I ran the Solistek HPS DE 10k finisher bulb for 7 weeks and then switched to the 10k finisher bulb for the final two weeks using the same 3 strains in the same room. Everything else remained the same in the test (same room, temps, nutrients etc.)
    My final results showed decreased yields under the 10k finisher bulb (12.3% less finished product per light on average. . . but on strain in particular had 22% lower yield!). I’ve taken the finished product into the lab to sample THC content (i’m assuming higher THC content in the UV lights, but I haven’t gotten results back yet). When I get results I’ll be happy to share them with you if you’re interested. Unfortunately their spectrum chart cuts off before it gets down to the UVB range.
    Here’s a link to the bulb:


    1. Unfortunately there can be many variables in tests like that. And normally, I recommend increasing the blue a little and decreasing the total brightness a little (10-15%) for finishing. I would assume a 10k lamp would be almost mostly blue, and I wouldn’t recommend that for flower ever, even if THEY do. As for UV, a Metal halide lamp in general should not produce measurable UVB, it is filtered out by the glass jacket.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s