Quote:
Originally Posted by sphelps
Bulbs with a lower K rating typically produce higher PAR because, as you said, it's related to the amount of useful radiation (more of it in lower spectrum bulbs). So if PAR and spectrum wear where directly tied together, as you stated, then with certain bulbs you would see an increase in PAR as the spectrum shifts in the lower K direction. We of course know this isn't the case and the article I linked suggests that the change in par and spectrum overtime are independent not dependent. The decrease in PAR is related more to the decrease in intensity not the shift in spectrum. Of course certain bulbs preform differently so some may be more effected by the spectrum shift but avoiding such bulbs is pretty easy these days with all the information we now have.
So just because an LED doesn't suffer the same spectrum shift as other bulbs doesn't mean the PAR rating will be unaffected, it simply means you won't notice a change in color overtime, only intensity.
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your forgetting those spectrums that were already in the two extreme zones of red and blue, where do they go? Those gets pushed further right into the 800nm (reds) range that we cant see, nor can corals utilize so you lose a good portion of the spectrum that you would if the bulbs were new, so you see a decrease in PAR output. The decrease in PAR is not just about the intensity decrease, losing red spectrum and blue spectrum decrease par values quite a bit as well
The way spectrum works is, too far right, the spectrum isnt used, and same goes for to far let. if the bulbs we had originally were spiked at 450nm and spectrum shift it to 500nm in a year, all that blue light turns into green. Corals dont utilize green light very well and the and useful PAR goes down. Then everything in the 650nm-700nm range literally just disappears from the usefull radiation spectrum and moves into IR range.