I found this article from Orphek LED that discusses PAR vs. PUR, specifically while the Cree emitters we know and love have higher PAR value a lot of that energy is not useable by the coral for growth. So while the Orphek LED are lower in PAR and may even look dimmer, more energy is useable by the coral. I thought this was an interesting claim and worthy of sharing.
http://orphek.com/led/2012/07/unders...l-wavelengths/