spectrum tweaking

Varinaut

Well-Known Member
Jun 14, 2020
169
322
For the past 3 years I've had 400 watts of 4000'K Bridgelux LED strips over my 2' x 4', 2-plant hydro system, and have been happy with 1-1.75 lb of quality, dried product per harvest, but, of course, we're always looking for that extra boost in quality or quantity. That said, a couple of shiny biological objects have caught my eye for the past year or so that promise faster/bigger/better harvests, so after educating myself sufficiently on building LED strips, I'm trying to "tune" my light for happier plants.

First, the Emerson Effect. Research has found that while both 660nm and 730nm are photosynthetically active, when exposed to *both* spectra in the right quantities and ratio -- like %5 of total spectrum should be 660nm with a ratio of 3:1 of 660:730 -- the total photosynthetic output is significantly higher than the sum of the output of each of the 2 spectra alone, suggesting a synergistic effect between processes driven by the 2 spectra.

Then there's the effect of 730nm on light-dark transition. Without going into fine detail, as the sun goes down, more and more of the shorter wavelengths are filtered out until, for a brief period just before nightfall, only 730nm and above hit the leaves signaling to the plant that it should transition from its day to night time processes. Without the 730nm photons, the plant takes more than an hour to transition. By illuminating my girls with 6W of 730nm for 6 minutes after lights out, the plant flowers on a 13/11 schedule, and should "finish" a week early.

So, getting the LED parts from Aliexpress, I put together 2 strips to add to my fixture, each with 10x 1W 660nm diodes and 2x 1W 400nm (to control stretch). These are on for the full 13 hours of the grow room "day." I also added 6x 1W 730nm diodes (you can barely see them in the photo in the middle of the strips). The 730s are on from the beginning of lights on and go off 6 minutes after "lights-off."

IMG_20230117_083711017_HDR.jpg


Here's a comparison of the spectra of what I started with, and what I should have now:

4000K-led-spectrum.jpeg
fullspec-spectum.png.png


The room was put on a 13/11 flowering schedule on 12/15, so we're into week 5 and everything's looking good. Though, the stretch was a bit excessive so I'll probably add 4 more 400nm diodes for the next run. I'll try to update grow progress, but the harvest window is around March 1 so a more complete report then. If any of you have knowledgeable input I'd be interested.
 

Varinaut

Well-Known Member
Jun 14, 2020
169
322
The girls are in week 8 of 13/11, and exposed to the "enhanced" spectrum for 2.5 weeks. With a hard target date of March 1 for harvest, they're looking on track, although, the Panama is maturing more slowly and could probably use an extra week; we'll see. The Diet Durban (the near plant) in particular, has some pretty fluffy buds, but with 3.5 weeks to go, I expect them to fatten up nicely. As for the effects of the added spectra, it's too early to say, but if nothing else, the girls *seem* to be maturing more quickly so the EOD 730nm may well be working as advertised, at least in that regard.
IMG_20230205_100011608.jpg
 


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