Will it reduce yield and quality.
If "quality" is secondary metabolites, I've not seen anything that indicates that. Given that blue heavy light in veg will tend to increase branching, it might be arguable that it could increase the mass of secondary metabolites but my sense is that would be an incredibly hard argument to make, in terms of a practical difference.
"crop quality" is also defined as the ratio of flower to above ground mass. In that case, using a blue light could be argued to increase quality because there's less mass in the stems. One of the reasons I like a veg light is not because the quality metric looks better (I don't measure weights like that) but because the plants are easier to work with.
In terms of yield, it might be that a there's a reduction in flower yield if you use a veg light (in veg) vs just going with a flower light all the way through. The difference? It would be a challenge to quantify unless you're in a lab. I've seen no research that looks into that and one paper that showed yield decreased as the percentage of blue increased but, IIRC, that was when blue was used throughout the grow cycle. I've attached the paper for your review.
Bugbee, and subsequently Westmoreland, have commented on "the optimal spectrum" and both have said that a white LED with some far red is "optimal" but, overall, the best approach is to get plants to their light saturation point and keep them there.
Will using a T5 in veg reduce yield or quality? On the latter, I've seen nothing on that; for the former, perhaps in a lab but, in the real world, a grow is subject to so many impacts other than what might be caused by a couple of weeks of a T5 that, for me, I take advantage of a veg light to impact plant morphology because, when a cannabis plant is given a lot of light throughout its lifecycle, the yield is truly staggering.
As an addendum - based on Mitch Westmoreland's videos of earlier this year (YouTube), the key to maximizing yield and secondary metabolites, my growing practice will be to keep plants at the light saturation point throughout their lifecycle while allowing canopy temp to reach up to 85° until the second week in flower after which the temperature of tops of the flowers should not exceed 78°F. The high temps and high light conditions maximize plant "build out" while the lowered temperatures help to reduce loss of secondary metabolites.
Below are couple of screenshots from Westmoreland's YT videos. I've read a handful of research documents that provide the details of what he shares in his videos but, if you want to not have to grind through that level of information, his videos are an absolute gold mine of "just do this".
In the screenshot below, note the caption in the lower left - it's all about the DLI.
In his video, Westmoreland reveals the hard truth - cannabis yield estimate is a function of DLI. Per Westmoreland, flower yield in grams is 0.2 to 0.3 * the number of mols of light the plant has received over its lifespan. The rationale for this is that the only way plants can grow is by using light to generate glucose which is then used for growth. There's simply no other way for a plant to grow than by using the glucose that it generates.
So a veg light will yield plants of a different shape but, overall, yield is a function of how many photons hit the canopy.
Long answer, no doubt, but there are no perfect solutions, only tradeoffs.
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