Yeah! I'd get that too. Perfect grow, everything was "correct", but still all of the above issues and what I described. I never experienced these issues under Single Ended Bulb grows, but once I switched to a DE bulb I encountered many new challenges I'd never faced growing under SE bulbs.
If we think about it, its a symptom of excess light. If our buds have that "hay" smell to them, that means chlorophyll is being "fried" by something. Consider that "hay/chlorophyll" smell is also a terpene, and what is producing that terpene? Excess light, I believe.
I cannot provide much other than personal anecdotes based on my own personal experiences. Google searches have given me the following citations from articles, but I'm still honestly not quite sure what questions to ask Google to get the information to confirm my theory. I recall coming across the term "Photosynthesis toxicity" a few years back, but Google searches have yielded me no results upon searching for that.
Here's a few excerpts and articles I came up with from my searching, but still nothing conclusive enough for me to believe my theory as fact.
Source 1
"Photosynthesis is a life-sustaining process by which plants store solar energy as sugar molecules. However, if sunlight is in excess, it can lead to leaves being dehydrated and damaged. To prevent such damage, plants dissipate extra light as heat."
"Previous research has shown how plants quickly adapt to changes in sunlight intensity.
Even in very sunny conditions, only 30 per cent available sunlight is converted into sugar, and the rest is released as heat. The excess energy, if not released, leads to the creation of free radicals that can damage proteins and other important cellular molecules."
“During photosynthesis, light-harvesting complexes play two seemingly contradictory roles. They absorb energy to drive water-splitting and photosynthesis, but at the same time, when there’s too much energy,
they have to also be able to get rid of it” (Or, perhaps not have the surpluss in the first place?)
Source 2
"Although light is the energy source for plant growth, excessive light can lead to depression in photosynthetic efficiency (photoinhibition), mainly due to oxidative damage to the photosystem II"
Its always week 5 this happens too, which is what triggered my brain into asking; "Why week 5?"
Eventually made me consider outdoor light cycles. Not sure about your location, but flower here starts early July and goes into Sept-Oct. So I thought, July-August is like weeks 1-4 of flower indoor, and Sept-Oct is like weeks 5-12 in flower indoor. If only 30% of available sunlight is used, this means the rest is excess.
The same plants that were doing everything in their power to grow into the DE/LED bulbs themselves if they could, were now suffering. Outdoors, the sun changes and is further away from the plants, as well as dimmer. I never considered this change in an indoor environment. Since dimming my lights at week 5+, I have had much greater results.
While I will readily admit dimming lights sounds like "stoner science", I've based it on the fact that fall sunlight is much different than spring/summer sunlight in terms of both intensity and spectrum. We indoor growers will change from MH to HPS bulbs to account for the spectrum changes between spring/fall, but not once have I seen anyone suggest dimming lights to "fall levels" as we observe the sun itself doing.
Furthermore, even in the summer, plants never deal with constant direct sunlight. The sun is moving outdoors; yet another thing we as indoor growers can forget to account for. Outdoors, it isn't 12 full hours of direct overheat sunlight, its more like 3-4 hours of overhead sun.
Try dimming your lights at week 5 and see if you notice any positive changes like I did. We can always dial things back to 100%, but cannot take any excess back. Especially in flower.
It has helped me quite a bit, and I'm embarrassed it took me so many years of growing to realize I needed to dim my lights. Seems incredibly counterintuitive, but it works. Of course, it is always something simple and plain that I have ignored.
Sorry for the book, I still do not believe the information is conclusive enough to confirm my theory at this time, but hopefully the information was useful to you in some way.
