Good evening fellow growers and members…I have been asked to create a thread centered on UV and Cannabis (or other produce items)…I would be honored to start such a thread but will need your initial guidance on topics that concern you the most. So please reply to this with what info or topics within UV and Cannabis you would like for me to begin with.
Thanks and cannot wait to learn together–which is the true power of Forums such as this.
Should commercial cannabis gardens be considering adding UV light or buying lights with a higher UV? Differences of UVA and UVB?
What would the outcome be of such an addition?
How would you easily be able to measure UV at your canopy?
keep the topics coming and I will review on Friday the topics and start rolling out communications within this thread starting next week.
Thanks @Nate
What duration or intervals should UV be applied ?
Should UVA or UVB be applied for hours or minutes, seconds ?
Is UV something that should be applied in both Vegetative and Flower ?
Different frequencies of UV ? Since UV-C and UV-B have shorter wavelengths (higher frequencies) and higher energy than UV-A.
What’s your take on UVC? Long story short, it kills stuff. Mold and fungus, yes, but also plant and animal cells. There not much of it naturally occurring on our planet, thankfully, because the ozone filters it out.
I think it’s a sketchy solution to mold problems. What do you think?
Uvc for mold and mildew abbaitment is old school.
Reme bulbs for the win. The bulbs generate peroxide ions that fall allover your rooms through being mounted in whatever HVAC plenums exist in said facility. Walls and plants included.
Google; R.E.M.E technology. Used widely in most healthcare facilities and the industry as a whole.
Greetings - just joined the forum.
I am a founding partner of California Lightworks, an LED grow light manufacturer based in Southern California. We have included UVB in our LED grow light fixtures since 2008. These were originally for hobby and medium size commercial growers using a T8 UVB bulb built into the LED fixtures. We are now launching a commercial version which is a more powerful separate UVB light that can be used with any grow lights in large commercial operaitons.
In a nutshell, these are some of the things we have seen:
Cannabis has evolved a protective mechanism which seems to be unique in the plant world to defend itself against high levels of UVB - which damages its reproductive cycle. This is only true of strains native to the equator or anywhere with natural levels of high UVB. Most strains native to northern or southern latitudes have not evolved this ability (hemp). Specific molecular senors in the plant constantly measure the level of UVB in sunlight. At a certain threshold level of UVB, the plant increases the produciton of a chemical that coats the trichomes and acts as a UVB filter. In what we like to call nature’s little joke, this protective chemical is THC.
Many LED manufacturers claim to include UVB (280 nm - 315 nm) in their spectrum but they are really talking about UVA (300 nm - 400 nm) - which is the extreme end of the deep blue spectrum and does have value for photosynthesis and plant metabolism - however, this has nothing to do with UVB. UVC (100 nm - 280 nm) is deadly and will kill anything living. UVC is a great steralizer and is used in many air filtration systems. UVB is also effective in some cases against mold but this is not the focus of our UVB applications.
Most UVB is filtered out of bulb based lights as it is quite damaging to the eye so there is very little in HPS, MH or florescent lighting. There are UVB LEDs on the market but these are extremely expensive and are not practical in a commercial grow light.
There are various studies on the details of the chemical process and how this functions at the celular level. Here is a link to our website on this subject: [http://californialightworks.com/uvb-light-and-thc-potency/]
This process is only effective during the last two or three weeks of flower when buds are well formed and resin is developing. There is no photosynthesis at the UVB levels (280 nm - 315 nm) so this is more a question of flipping a switch rather than building up the light effect over time. There is no advantage of using UVB all during the grow cycle or even during the full 12 hour day cycle. However, the process does seem to be linear - the higher the level of UVB - the higher the THC reaction. We generally recommend two to three hours of UVB daily during the last three weeks of flowering.
In practice, we have seen increases in THC level on the same strain of as much as 25% using supplimental UVB. Obviously, this varies by strain and the intensity of the UVB.
In hobby lights, we use a low power T8 UVB bulb which is similar to a reptile habitat bulb. These are pretty effective from 12 to 24 inches and do not pose a huge risk to humans. The light drops off quite quickly at higher heights over the canopy.
For commercial applications, we are finalizing a much more powerful UVB light that can be hung much higher over the canopy and can be used with any type of grow light or even the sun. The problem is that higher level UVB is much more damaging to the skin and especially to the eyes.
We are currently running tests in large scale commercial grow operations where there is an automatic switch that turns off the UVB when anyone is in the room. This is the primary design challenge with this new light.
We should have more data on these test over the coming weeks. We will have photos and lab results which we would be happy to share.
More to come…
We welcome any additional information or experience in this area!
Thanks for the info! I’m writing a report on the latest in LED lighting for cannabis growers. It’ll analyze the current product offerings and reflect on the tech thinking behind design. I’m particularly interested in the “white” vs. red/blue debate.
Do you know where I can find academic research on LEDs? Info specific to cannabis would be invaluable. Third-party testing of LED lamps would be great too.
@jbohannan8 you should speak with @igodfrey, he has been conducting some research on the LED industry.
Thanks for your thought Nick, good idea. Appreciate your help.
Hey Jack, a good place to start with academic research is scholar.google.com everything is cited and sourced. Most studies are on lettuce, tomatoes etc. but you can still use most of what you find. LED magazine and IES - Illuminating Engineering Society will help get things moving too.
Hi everyone, great discussions across this forum so far! I’m starting to reply to some of the threads relating to lighting since my background is in optical engineering and the study of light. I’m a Ph.D candidate in the field currently and extremely interested in the cannabis industry!
@clones Fantastic review! I’ve looked at using UVC/UVB LED’s for a water purification project before and it was interesting to find this thread of UVB use in cannabis. You mentioned studies that document UVB uptake and stress response, and in your website post you mention that the chemical production of malonyl-CoA from the stress response is used by cannabis “to make Olivtol, which it in turn uses to make THC”, is there documentation on this? I’ve looked but can’t seem to find the review or study on it and would love to read it!
Due to the high energy nature of photons in this region, I would be hesitant to introduce this wavelength into a grow space because of the damage induced to humans, especially in the eye as was mentioned in this thread. We have done studies and other studies can be found on the damage threshold of the eye (specifically the cornea) at various wavelengths. UVB is highly absorbed in the cornea leading to a number of concerns over time. Therefore, I guess I’d pose a question of what the cost/benefit relationship is with introducing UVB LED’s for higher THC production vs. the safety of cultivators and the precautions needed when using this wavelength?
Here are some interesting reads I found to bring me up to speed on UV use in cannabis and Iook forward to learning more on the subject from this thread.
Solid Q&A Intro
https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-015-0156-y
A more involved review of UVR8 and it’s impact on plant structure
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3963570/
I’m curious, do you know if there is an established “safe” UV-B exposure limit for workers (IE the radiation dose limit for radiation workers)?
@Hunter: The link you referred to deals with radiation emitted from radioactive sources. Typically this radiation is in the form of alpha, beta, neutrino and EM radiation. However, the EM radiation is in the gamma and x-ray portions of the EM spectrum which have significantly higher energies that UV. (Atom destroying!)
I’ll try to post the damage threshold curve and the calculation for radiation exposure in the UV range for the eye later today. Sorry for the delayed response.
Dr. Marc Van Iersel from the University of Georgia is leading the way in LED technology and plant communication. If you google him you will get information on his current and past research.
http://www.ashs.org/news/288543/Biofeedback-system-designed-to-control-photosynthetic-lighting.htm
I have been testing a light bar from Fluence that emits UV. I only use it during the last 4 weeks of flower, when the trichomes really begin to develop. However, LEDs are also my main source of photon energy, and we found some interesting things. Fluence has other growers, who are using traditional DE HID lighting, and found that when those growers used the UV light bar, they increased their trichome density (not increase in potency, but in volume of oil) per square millimeter of calyx. When I did my trials, I saw less trichome density increase, but what that means is the the LED fixtures being used as the sole source light were already increasing the density.
As far as using UV light for disinfection of irrigation drain water for the purpose of recirculating the drain water…this works very well. In greenhouse ag, we have been using UV units for 20 years now to disinfect the drain water of pathogens. There are many climate control companies who produce these UV units for this purpose. I personally have used the Priva Vialux and Hortimax Vitalite units before. I like the Hortimax unit as it has more surface area of contact with the UV lights and the water flow thru the system is slower, thus allowing a more thorough disinfection to occur. We’ve also used a custom unit controlled by a Hoogendorn system as well. I am currently using Hortimax for all of our cannabis projects.
http://www.hortimax.com/7/18/89/en/news/hortimax-launches-new-uv-disinfection-unit.html
@jbohannan8: I get alot of my research material on LED’s from OSA. They have papers in a couple areas that I was interested in. Photodegradation of the phosphor coating on white LED’s, substrate materials for LED’s (efficiency type reviews) and a lot of others. An account is like $300 for a year but I find it extremely useful.
@Dsolomon: Do you know how much UV power is being radiated from that light bar? And what has your experience been using Fluence’s lights? When I read up on them it looked like they were using a spectrum built mostly form white LED’s as opposed to most other who use just the 451nm and 660nm approach. Any benefits that you’ve seen in your growing with one spectrum over another? Also, super interesting that the oil volume increased rather than the density which seems like the plant is trying to mitigate the stress response through a higher production of oil rather than increase the concentration of UVR8 homodimers. I wonder if this drops the other plant mechanics like photosynthesis etc.during the UV lighting.
@Hunter: We are about to get into the weeds here…
CNIRP EL standard says that 3mJ/cm^2 is the limit for ocular exposure for wavelengths between 180nm - 400nm. Let’s call this variable lim.
The max exposure time based on Bunsen–Roscoe law or the rule of reciprocity (irradiance vs exposure) can be found by
t_max = lim/E_eff
E_eff is the irradiance of light on the cornea. Let’s look at a UVB LED at 265nm
The optical power output is .35mW and is roughly a 3x3mm emitting surface
The irradiance from the source can be found by E_source = .27L_sT*D_e^2
L_s = radiance of source
T = transmittance of cornea based on age
D_e = diameter of the pupil
Therefore: E_source = .27*(4.126e-4)(.85)(4mm)^2 = 1.515e-5 [W/cm^s]
E_eff = E_source*S(265) = 1.439e-5 [W/cm^2] S(lam) is the UV hazard function
So coming all the way back
t_max = (3mJ/cm^2)/1.439e-5 [W/cm^2] = 208 seconds
Keep in mind that this assumes our eye is looking directly at the full source but with large enough power this does become a concern. Mechanisms can be put into place to shunt the UV light with workers in the space but I was more or less surprised that UV was being used at all in the space. Science rant over.
Paper for calculations: David H. Sliney, Peder Fast, and Anders Ricksand, “Optical radiation hazards analysis of ultraviolet headlamps,” Appl. Opt. 34, 4912-4922 (1995)
@shibbyhockey04 Thanks for the analysis! 208 seconds is a long time to be staring directly at a UV light. Is that a maximum for a person’s lifetime, per year, or some other time period?
That exposure time is based on continuous exposure. Damage in the eye is cumulative since the repair mechanisms in the areas of damage aren’t super robust (better for scratches and things of that nature), so after this time frame damage will begin and subsequent exposure further increases the damage, usually causing cataracts. The exposure time is for one single LED, so yes 208 seconds is a long time but add one more LED and that number drops, so with a fixture outfitted with multiple LED’s I’d start to get a little worried.
There are plenty of ways to mitigate this problem, I mostly bring up the point so that anyone using tech like this can ask the proper questions for safety!
A simple standard polycarbonate safety glasses shields 100% UV…with regards to working underneath the LEDs…the power drops exponentially with distance so a study conducted by the Association of Industrial Hygenists showed that it would take working 18h continuously per day to be affected by UV. The typical exposure times and application timing during harvest cycle would never reach those daily levels.
I would be skeptical to see Fluence’s “UV”—not all UV is created equal…a 400 nm UV LED is far different than UVB (280-320) for example. It targets different pathways within plant or no pathways at all in some cases.
I apologize the lengthy delay in responding to my original thread…but I have been tied up in some non-disclosure aspects and working through the legal stuff to get info out to everyone.
Again my sincerest apologies.
Dr. Peter Barber, MBA
Product Marketing Manager
