I watched the webinar and I also did a little bit of research afterwards. We need to clarify that Valoya did not test THC levels in the UV vs Far Red experiments – only CBD. Perhaps their THC results were not what they had hoped for. I would expect that if they were, they would have published them. It is even stranger to me as most growers are more interested in THC levels than CBD. Or they are at least interested in both.
It's also interesting that the figures below do not add up. Simple maths says the Blue:Green ratios are incorrect and so are the Red:Far Red ratios. For example 39.7% Red to 3.8% Far Red is a ratio of 10.4 (not 12.3) for the Control, whilst the UVA + FR ratio is actually 9.1 (not 8.2). The UVA+ ratio is correct. Looking at the Blue:Green ratios, they are correct for the Control, but not for the UVA+ and UVA/FR+ lights.
Sloppy maths is sloppy science. If basic ratios can't be calculated correctly, then who knows what else is wrong? I'm not going to pick holes in every chart but simply point out that there appear to be quite a few mistakes in the presentation that may cast doubt on the numbers.
I also want to point out that even though the UVA/FR+ LED had 385nm diodes compared to the Control LED having 405nm, the Control had significantly more cannabinoids. This is attributed to lower levels of Far Red light – even though the R:FR ratios are quite close (10.4 vs 9.1). It would have been more interesting to me to see the same levels of Far Red light where only the UVA is changed from 405nm to 385nm – that would tell us if indeed 385nm is better than 405nm because this experiment is inconclusive in that respect. In fact, it appears to confirm our belief that 405nm is just as good as UVA in increasing cannabinoid levels, as that's what the Valoya experiments showed.
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I also want to mention that the Valoya experiment appears to contradict what outdoor growers have found, which is that THC and terpene levels in outdoor plants (when grown properly) can actually be higher than those grown indoors under lights. Here is one reference for that statement and there are others online.
https://weedmaps.com/news/2017/01/indoor-vs-outdoor-weed-a-visual-guide/
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Sunlight has a very low Red:Far Red ratio in the region of 1.4. That ratio varies at different times of day and season, but it is still a very low figure compared to indoor lighting. Even HPS has a R:FR ratio of around 2.8-3, which is twice as much R:FR as sunlight.
To be fair there are other experiments that have been done that do agree with the Valoya presentation. One of them is here:
https://www.karger.com/Article/FullText/489030
The highest THC percentages came from plants with the lowest amount of Far Red (higher R:FR ratio). The LED lights that were used in the above experiment also happend to be supplied by Valoya!
One phenomenon that may be happening is that in all the research we have read there seems to be a trade-off between yield and cannabinoid levels. That is to say that two plants of the same strain grown under different lights can have different yields and cannabinoid levels, but in many cases higher yields lead to lower cannabinoid levels and vice versa. It is almost as if the plant produces the same total amount of cannabinoids and only the yield changes. If you have higher yields with the same cannabinoid content, then the percentage of cannabinoids per biomass will be lower. This has been observed many times but I still can't say whether there is a linear correlation between the two.
If anything we have noticed that LED tends to produce higher cannabinoid levels and almost the same yield as HPS. HPS is very hard to beat for overal yield. LED can easily beat HPS on a yield per watts basis but when the grow area and conditions are the same, HPS can rival or beat LED for total yield even though it uses more power. I suspect this may have to do with HPS producing more stem weight in each flower compared to LED, as LED flowers are nearly always more compact and higher in cannabinoids.
As for the rest of the presentation, I don't have any real issue with it as it reinforces what we have said all along, that a small amount of UVA/near-UV can have quite a large effect on cannabinoid production compared to standard white phosphor LEDs that contain almost no light below 430nm.
