Quote:
Originally Posted by OceanicCorals-Eugene-
PAR decreases as spectrum shift due to a few factors. PAR is a measure of Photosynthetically Active Radiation as bulbs shift in color they generally move either towards the right of the spectrum graph or the left, most bulbs we know move towards the right as can be seen in high kelvin bulbs as they go from blue to white-ish. As this happens PAR values drop as the spectrum is now shifting and you get less of both red/blue spectrum that most corals utilize. The point is even if the PAR is still high enough the corals no longer get there needed spectrum so there colors become dull or brown and none of us like that  |
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.