Prawn Connery wrote: ↑Mon Jun 24, 2019 7:19 am
Yes, on paper they are good LEDs and have a good range from 367nm to 420nm. Seoul Semiconductor are pushing their UV mono LEDs and UV-based white phosphors - which we use on our High Lights - for the horticulture industry, because they understand the importance of full spectrum LED with added UV to target secondary metabolite production.
Or at the very least, they understand that trying to match broad-spectrum sunlight - in light (pun intended) of our ever-changing understanding of how different spectra affect plant growth - is a great marketing gimmick!
I don't pretend to be an expert on the subject, so can only offer some observations. Firstly, I don't know where some of these companies get their ideas that 285nm and 365nm are the most efficient sources of UV for plants, as I haven't seen any real scientific basis for this. They may be based on one particular study that exposed plants to UVB or not, but other more recent studies have shown that pretty much all UV light will elicit stress responses in cannabis that increase cannabinoid production.
It seems logical, therefore, that the higher the frequency (lower nm) and energy of a wavelength, the greater the stress response in a plant over a given timeframe.
However, the trade-off is that these stress responses are exactly that: responses to stress factors (DNA damaging UV light) that would otherwise harm the plant.
So UV light can force a plant to produce more THC, but it can also damage the plant in the process and stunt growth. It may also be a very inefficient use of energy, as the energy required to provide UV light is not helping the plant grow.
The tradeoff, therefore, is THC production vs overall yield.
My own view is that there is probably a balance somewhere, between optimum use of UV light to provide a mild stress response to improve terpene and cannabinoid production, and wasted energy/damaging UV that either stunts growth, damages the plant, or does not promote growth - resulting in lower yields.
Very few growers want lower yields. And quality can be very subjective.
I have smoked UVA/B exposed buds and non-UV exposed. The UV exposed bud has been grown under lights, and grown outdoors.
You can clearly notice the difference in potency - it is tangible (even if you don't have a mass spectrometer to measure THC levels). But does it improve the experience? Is the quality of the high "better" or just "stronger". And if it is merely "stronger" (higher levels of cannabinoids), then does that make up for any lack of "quality" in the high? By which I mean, a strong, nasty (paranoia-inducing) high is still a nasty high.
Increasing THC production when other cannabinoids are not increased by the same proportion could, in fact, ruin the "high" profile and turn what may be a pleasant smoke into something a little less pleasant.
Nearly all of today's modern strains were bred under almost no UV (HPS lights, or sometimes Metal Halides that usually had UV-blockiung iron incorporated into the protective glass).
Even plants that evolved outside where never subjected to high levels of UVB: 285nm almost doesn't exist on our planet, as it is nearly all filtered out by the atmosphere. The UVB to UVA ratio averages around 20:1, and even that only makes up around 5% of all light energy that reaches the earth (meaning UVB makes up 5% of 5% - or 0.25% of all light energy). And of that 0.25%, only a tiny, tiny fraction is 285nm - if at all at sea level.
So if we are really using sunlight as the yardstick when creating artificial light, then we probably only need 5% maximum UV, and of that, 95% should be UVA. And it should probably be broad spectrum UVA, too - not just one wavelength.
But as I said, I'm no expert, and these are only my observations.