What is PAR

[JoshHarpst]

What is PAR? I have heard about it but don't get it. Thanks
~Josh

 

[jeffbrig]

Photosynthetically Active Radiation

Quick google link

PAR is defined in terms of photon (quantum) flux, specifically, the number of moles of photons in the radiant energy
between 400 nm and 700 nm. One mole of photons is 6.0222 x 1023 photons (6.0222 x 1023 is Avagadroââ"šÂ¬Ã¢"žÂ¢s Number).
The Photosynthetic Photon Flux Density (PPFD), i.e., the photon irradiance, is expressed in moles per square meter

 

[IndyReefMan]

PAR is Photosynthetically Active Radiation. It is a measure of the "amount" of light that a bulb emits that is useful for photosynthesis. It is applicable in our hobby since most corals harbor symbiotic algae that reside within their tissues. These algae utilize photosynthesis and produce by-products that are beneficial to the coral. At least, that's my understanding of it.

 

[RobbyG]

In simple terms It's a measurement unit for the amount of light energy across the whole visible light spectrum. Different from other measurements that may only measure specific wave lengths or include light outside regular visible wave lengths