We’re (or at least I’m) not. But the easiest way to account for the likely increase in photosynthesis from UV-A in cannabis would be to boost PPFD (a better way would be to boost 400-450 nm to match the UV-A umol/s/m2).
You can kill plants with too much PPFD or DLI, but the mechanisms of damage are different than the DNA damage from UV.
Also, once you exceed around 600-700 umol/s/m2 of red light photobleaching often occurs in cannabis. Which leads to dead flower and leaf tissues. So, yeah, you can do extreme damage to cannabis with PAR photons (specifically red range photons due to their effect on tissue temp, chlorophylls, light saturation, etc.).
Not sure how that matters though, because hopefully no one is adding too much UV or too much PPFD and DLI.
PPFD is a spot measurement only if a grower is measuring in one spot or doesn’t have photometric modeling of their space. Plus, bar quantum sensors are great, which are 3’ or 4’ long with multiple senors to average readings for a greater measurement area.
Every facility I design for clients or employers come with full photomteric molding (using DIALux) so a grower knows the PPFD at any given spot at multiple planes. And those data can easily be used to find the PPFD at any spot and any distance from the floor (plane).
Yes, for many species (see below). Most people are wrong because they don’t read scientific literature, instead, they read forums and attend the YouTube University.
UV-A, at least the higher end of the range greater than about 360 nm, has been found to be photosynthetically active many species (e.g., tomato) but not always for others (e.g., lettuce). The photosynthetic capacity and net photosynthesis tends to increase as the wavelength band widens (e.g., 390 nm); as does the increase in growth rate and biomass. The closer to 400 nm the better in terms of UV-A. And indoor cultivation tends to allow for greater photosynthetic increases from UV-A than outdoor cultivation.
UV-B damages photosynthetic capacity, doesn’t increase cannabis yield, delays flower maturation, and at worst (typically) reduces cannabis yield when applied throughout an entire grow.
While UV-A below about 350 nm damages the photosynthetic apparatus leading to a reduction in the maximum quantum efficiency of photosystem II (PSII) and net photosynthetic rate. So, narrow UV-A damages the photosynthetic capacity just like UV-B.
This study didn’t find an increase in Pn (net photosynthetic rate) from UV-A for chemotype I plant (Larry OG) using a Fluence Bioengineering Ray44 LED with “UVSpec” (UV-A at ~390 mm and ~66 umol/s/m2). But there also wasn’t a decrease in Pn. The control (PAR) PPFD was from SPYDER xPlus LED fixutres from Fluence as well.
And many factors come into play which can determine whether UV-A increases, decreases, or has no effect on Pn. So just because this study didn’t find an increase in Pn for Larry OG under their experimental conditions doesn’t mean cannabis Pn doesn’t increase with UV-A.
Here’s the effect of UV-A on photosynthesis for Larry OG:
The mass medical bar is frequently sold out. A person could copy their design easily to make their own, I’m sure.
From what I have read (on here), the uv diodes burn out about twice as fast. So it seems a better idea to place them in a bar, as compared to scattered in the fixture, but then that would seem more difficult to achieve perfect uniformity.
Let me tell you here that I don’t want to prove anything. I’m an ordinary home grower, don’t believe me, I’m just sharing my story. uvb from the end of week 5 until week 9 in the morning 1 hour before the power goes out for another 1 hour. I can’t check the whole tree because it costs money. So I choose the main flower of both sides to send for examination. whatever the result I received my results 4/23/2023, it’s my latest family.
Agree 100% Ralph, been in the lighting game for 30 years and have growers every week looking for the UV and FR silver bullets.
Work as an agent for the biggest horticulture lighting company in the world and seen the R&D they do - spend $$$ with seriously clever people.
Bottom line for lighting IMHO is -
Get your DLI as high as possible (if over say DLI = 35) then add CO2 1200ppm.
Take care of the other parameters and you should be golden.
Phytochrome and Cryptochrome activation will cause exponentially more metabolic activity than simply using PAR lighting and trying to exponentially grow your DLI. As. Matter of fact this metabolic activity is what allows for high input gardens. EC into 11, CO2 near 3000ppm peak, etc.
Phytochrome and Cryptochrome are activated with FAR Red and Ultra Violet radiation respectively.
Thank god light salesman aren’t responsible for the science behind botany.
