Deep red and far red diodes

[The_Mouse_Police]

Fair enough. I will post my results when I have them.

Is there any reason why people tend to solely focus on adding red and far red as opposed to adding both reds and blue? Or is it just what is popular right now?

Blue is already there, and easy to get more of. White LEDs are based on blue LEDs, generally 450nm, which is very close to the chlorophyll ideal, and close enough to UVA to trigger most plants', "I'm getting a lot of summer sun, so need to stay bushy and produce oils, terpenes, etc.," responses. The higher the CCT, the more of that native blue is left (CCT *generally* correlates well with blue:red ratios). So, using 5000K instead of 3500K would be equivalent to adding more blue, I think on the order of +20%, but don't quote me on the relative amount. In addition, blue LEDs under about 440nm have low efficiency and efficacy, so more 450nm tends to be more cost-effective than closing in on 430nm.

Meanwhile, because most 80 CRI white LEDs (all the common ones, today) peak so far away from 660-680nm, some peaking as low as 620nm, specifically adding 660nm can be more efficient than going further down in CCT to get more red for chlorophyll A. Chlorophyll B's response curves are a good match for many white LEDs, from the start, especially those with lots of red around 640nm. The Samsung's, FI, almost all have their red-orange peak around 620nm, which is low for chlorophyll A and B.

Then, looking at it more from the angle of the McCree curve, the red hump is severely low in most white LEDs, compared to the McCree response curve, which gets very active towards 700nm, as the white LEDs' outputs are trailing off, while the green and blue ranges aren't so bad off (and are easy to adjust for with emitter selection). Adding more energy alone works, but also increases energy that the plant must get rid of as heat. Absorption of, "close enough," frequencies is less efficient, and the energy not used for chemical reactions has to go somewhere.

[ViridisHC]

I see and that makes sense. Wondering would adding blue with red be beneficial then, not so much, or would it possibly be harmful if plants are already getting enough blue light from white LEDs?

[The_Mouse_Police]

It would be fine, if you want more, and some people do just that, usually adding intense blurples. It effectively adds to the amount that the white LEDs already put out, and you can get some decently efficient 440nm emitters, too. Before dropping off the face of the Internet, Photon Fantom Design's WaVy board was a white QB with added blue and red diodes mixed in.

Some plants respond really well to narrow band red and blue supplementation, like most mints, and especially basil. It can also help speed up ripening for tomatoes and peppers under artifical lighting. However, it also means relatively less green, and more green helps tell the plant that it needs to grow more. So, outside of oddballs like basil, it may not be good for the whole life cycle.

It's easier to just stick one kind of QB or strip in there, and consider the setup good enough. Whether you are better off with a complex tunable spectrum (and schedule), a fixed pre-tuned spectrum from different emitters mixed in a system, or just one SKU of PCB mounted diodes, is an open question. There are many variables within light itself (well, PAR), and then light is just one category of many for your grow.

[Vividled]

Hlg along with the awesome R spec qb288 v2 also have a range of extremely efficient high end supplements. Blue, red, far red and now uv. I'm stocking them and experimenting myself along with a couple of close customers. It should be very interesting to see the results especially with the uv supplement as this hasn't really been documented yet.