PAR not the definitive measurement? PAR vs. PUR
 

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/

Thanks for posting it, its a good read for sure.

Playing devils advocate the company makes lots of claims, would be nice to see some actual studies or citations at the end of the post. It also discourages me that I can move my cursor over slightly and purchase their product.

Oh yes. It's their site designed to sell a product no doubt but the information is straight forward and if correct could be used when purchasing any LED for coral propagation regardless of brand.

seems like they are comparing apples and oranges... if u compare any 16000k K bulb with any 7000k bulb you will get different spikes in a spectrograph!!... more studies needed for sure

While the theory behind PUR is pretty sound the problem is it is still all theoretical and it's important you recognize that. Nailing down what spectrum all your corals benefit most from is virtually impossible as not only do different corals use different wavelengths based on depth and origin but they are also capable of adapting over time. PAR is still an accurate way of gauging usable light as it measures light within ALL usable wavelengths, to start nitpicking stating otherwise or more likely a way of justifying lower par values. Remember the bulbs and LEDs we use are already focused in on what corals tend to use more in general so realistically PUR theory has already been accounted for before we even break out PAR meters. Also consider most hobbyists agree from experience a 10K bulb promotes better growth than a 20K which supports PAR yet goes against PUR theory.

My DIY LED unit uses 454nm blues, 6500k, 10000k & 20000k (at least that's what the manufacturer states) wavelengths. I used so many different LEDs to try to account for both PAR & PUR requirements. My theory is that LEDs are more like a rifle shot approach in terms of narrow band wavelengths, so I spread them out to achieve more of a shotgun approach. The corals seem to like the light.

Pretty much all that really matters! All the main stream LED fixtures seem capable of growing coral just fine regardless of PAR or PUR battles. I haven't heard of any well made DIY LED fixtures having coral growth problems either.

I was thinking the same thing. :wink: