PAR explained?

[6Speed]

Can someone explain to me what PAR is, exactly? I gather that it is the intensity of the light, but I'm not sure how big of a difference, say, a PAR output of 270 from one lamp, to 330 from another.

It seems like a 6500k 250w lamp will put high 500's in PAR, while a 20k will only put out around 250PAR. That seems like a huge difference to me, and I wonder how much greater growth you would see from the extra 200+ PAR, or even if you would see that much difference?

 

[Giovanni]

Along for the education. Maybe someone can point to a good reference.

 

[6Speed]

Anybody? I wasn't sure if this was the right forum, but it seemed the closest match.

 

[ulua56]

http://www.reefkeeping.com/issues/2006-04/sj/index.php

 

[poedag]

Basically it's the amount of usable light for photosynthesis. Different intensities and spectrums have varied PAR. There are many factors that can increase/decrease PAR, including the amount of direct vs. diffuse radiation. For example stratus clouds that may decrease total radiation, might only decrease PAR by a small percentage. It just depends on the type of diffusion. What you ideally would like to go for in an aquarium is the highest PAR for the lowest power with the most ââ"šÂ¬Ã…"œpopââ"šÂ¬Ã‚ to make your corals shine. Iââ"šÂ¬Ã¢"žÂ¢ll leave it to others to figure out what the right combination is. Hope this helps -