Quote Originally Posted by glutek
hi
first I have to mention that i didn't manage to read all the news on 'perfect grow' so forgive me if I ask/say smth that's not new..

knna, could you please gimmie a hint where should I buy small numbers of LEDs in EU? do you live here actually, I noticed you removed Spanish flag from the profile?
In EU there is little good choices for getting LED directly from distributor on small quantities. Just LED shops, that charges large margin profits and often not inform about bin being on sale. LED tech, LED1, dotlight...

For little leds, i use dealextreme. Its from honk kong, but they send you the items (less than 100â?¬) without any problem. Competitive prices with free shipping. But they are more especialized on top end white leds, although sometimes they have some decents of colors.

Im currently doing a group buy of leds and constant current drivers (from mains). At manufacturer's price, top bins (SSC P4 red 635nm [email protected], Crees Royal blue (group 15) and white (Q4-Q5)). 1.94, 3.3 and 2.4â?¬ respectively. CC drivers less than 10â?¬. If you are interested, send me a PM.

Quote Originally Posted by glutek
btw, I wouldn't say cannabis is little demanding about light quality (otherwise we could grow under MV ie.), better to say it's just resistant as a weed and grows quite good under different conditions. just a better word.
When i say is little demanding, its on the sense it requires little (if any) of any given wavelenght. Its a different thing if it performs better using certain spectral distributions.

Cannabis had been grown under MV lights. They were displaced by HPS and MH (that are enhanced MV bulbs, BTW) due mostly the superior energy efficiency. More photons per watt=more yield per watt.

Spectrally, MH are superior to HPSs, but we already know that except very special conditions, at equal wattages HPSs produce more, just because they emit more photons per watt. Some people choose to use MHs at a cost of lower yield because they prefer the quality, but cannabis production is mostly determined by photons absorbed by plants (given there is no other limitant factors, that shouldnt on a well designed grow room).

The main parameter to know perfomance growing cannabis of a given bulb is how much photons per watt burned it emits. And HPS rule here. Until this year it has been impossible to get same photons per watt using LEDs, and spectral advantage only compensate partially that.

Quote Originally Posted by glutek
wheat is a monocot so not a best comparison. still good, as most important photoreceptors are so old origined that are found ubiquitus, and crys are found in likely all animals, including mammals, as humans, for sure
I'd rather say cannabis will benefit from more complex spectrums. but in this topic I mostly wanted to ask for a hint at the moment, dont really know if I want to talk about quality here. thanx a lot in advance
Yep, i know wheat and cannabis are very different. I just use it as example of a very well known plant that is almost light quality insensitive.

Quote Originally Posted by glutek
another question.. do you think(have you experimented) that in vivo it doesn't make a critical difference to have equal quantity of photons at, say, 10 or 20 nm away from 660 and other peaks? as we know from mcree and inada it doesn't affect photosynthesis rates much, but what about the overall effect?photomorphogenesis, plant architecture?
Yes, i have experienced that. I think is good to use both 645 and 660nm red light in order to avoid electron flow imparements between Photosystems I and II that may reduce quantum yield. But it happens mainly at high irradiances. When using medium-low irradiances (below 500 uE/m2), there is little difference on using 660 or 635nm.

For that reason, i choose to distribute the light evenly (to avoid high puntual irradiances) and use LEDs that emits the most photons possible per watt burned. Currently, 635nm ones. Its sad that most radiometricaly efficients AlInGaP leds emits at 654nm, which is almost perfect for us (maximum quantum yield (10.3 photons per O2) recorded was using a 657nm peaked led) but manufacturers dont do it (i dont know if LedEngin uses AlInGaP chips, but i doubt it, as effciencies are about 21-22% and its possible to get over 40% with known technologies. Maybe its just a patents issue).

Photomorphogenesis is mostly driven by blue light (cryptochromes) and red/far red relationship (phytochromes). From 620 to 700nm is red light, so there is little difference on using a peak 20nm ahead. Practical differences are negligible.