Its a very interesting approach. Blue light is mostly use for signaling and it don't needs much blue to see an effect. You need only 10PAR/w of blue wavelengths per squaremeter to keep the plants compact and support branching. I've seen such short nodial distance under blurple fixtures with lots of blue light like the Viparspectra LED's.
I've done my own experiments with additional blue 420-430nm LED's and the effects are clearly visible. Also the terpene profile is changing with more blue wavelength.
The diodes he has used are the cheapest he could find(3ct) but there are many other cheap solutions one can use.
These 12v, 1,2w modules for instance are available in different white spectrums as well as with red, green, purple or blue diodes and you can get them pretty cheap. And they are IP67 rated and run with a 12v driver so there would be no risk causing a fire. Maybe one or two modules mounted in the area where the stems are still soft are already enough to cause an effect and these midpower diodes would cause no burnings even when touching the stem.
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Its for sure worth a try. 20 of these modules you can get for less than 10 bucks and we all have a 12v driver laying around and if not, a 12v/1A wallplug power supply costs 3 bucks shipped and is enough for 10 of these modules.
Maybe a trick to win the next party cup competition, lol! The plant which is grown with multiple nodes per inch looks deffinately like a keeper. I have a little 3sft area for testing pourposes and these modules are already on my wish list. I've a few stretchy sativa strains currently(BlueDream, SSH and ColumbianGold/LemonGreen) who actually offer to try it out.