What does PAR exactly mean in lamens terms?

[dennis_said]

I see the numbers at cnidarianreef on PAR for particular bulbs... is higher better? What does it exactly contribute to? Better coral growth?

Thoughts? Sorry, just a noob looking for a quick and easy answer =D

Thanks!

[hmoore]

Photosynthetically Active Radiation (or usable radiation). A higher PAR value is supposed to mean more radiation in the region of high absorption as it relates to zooxanthellae uptake.

[reefboy6]

PAR = photosynthetically available radiation....i.e. the amount of light energy actually available to symbiotic zooxanthellae algae for converting into food. The higher the PAR, the more actually useable food energy a coral has available to it. Hope that helps.
Cheers,
Steve

[dennis_said]

So higher par contributes to more food for the corals? Faster growth?

[Peabody]

Not just that, but some animals (like SPS and clams) need MUCH more PAR to live than othe animals.

[hmoore]

I looked around and seemingly the Atmospheric Physics guys (like me) use the term as Photosynthetically Active Radiation and P. Available Rad. interchangeably. Interesting! It's the same thing (I guess).

[photobarry]

PAR light meters measure light in the red-violet range and (at least the scientific models) give equal weighting to every wavelength in that range. That means that one MH bulb with a large blue peak and another bulb with a large red peak could have the same PAR measurement but one would obviously be better for our usage. I have been seeing a lot more people use the term PAR lately, so I think this was a good question. I think it is being improperly used in a lot of cases, especially when people say that corals need PAR. Obviously, a coral needs light that falls within the spectrum that its symbionts can use for photosynthesis. So, saying a coral needs PAR doesn't really mean a whole lot. Since coral symbionts don't use each wavelength equally (unlike how the meter treats each wavelength the same), different spectrum lamps with the same PAR values may result in different reactions from the coral.

[saltshop]

Originally posted by photobarry
PAR light meters measure light in the red-violet range and (at least the scientific models) give equal weighting to every wavelength in that range. That means that one MH bulb with a large blue peak and another bulb with a large red peak could have the same PAR measurement but one would obviously be better for our usage. I have been seeing a lot more people use the term PAR lately, so I think this was a good question. I think it is being improperly used in a lot of cases, especially when people say that corals need PAR. Obviously, a coral needs light that falls within the spectrum that its symbionts can use for photosynthesis. So, saying a coral needs PAR doesn't really mean a whole lot. Since coral symbionts don't use each wavelength equally (unlike how the meter treats each wavelength the same), different spectrum lamps with the same PAR values may result in different reactions from the coral.

Nice post Barry...and from there we move on to PUR which rhymes with burr which is what it is like outside. :D

[harper]

I know Dana Riddle was a huge fan of PAR or PPFD (Photosynthetic Photon Flux Density), but haven’t seen a lot from him as of late. I always wondered how much photocenters differed for deeper water adapted corals verses terrestrial plants. It would seem reefers are inclined to use lamps heavy in the blue spectrum. Seems to work. Not sure if its more to bring out better colors due to UV blocking compounds or if in fact the symbiotic algae of different corals contained adapted photocenters with more carotinoids capturing energy from blue light. It would seem much of the coralime algae is adapted to use blue light. Anecdotal evidence points to Iwasaki lamps being the king of growth and PAR. However they also have a very large blue peek, IIRC they even eclipse most 20k lamps. I guess it would matter if your plan is to keep SPS from a few feet verses LPS/SPS from deep water. My opinion PAR is the least interesting aspect of a lamp. I am much more interested in other peoples experience with a lamp and aesthetics.

[photobarry]

Originally posted by saltshop
Nice post Barry...and from there we move on to PUR which rhymes with burr which is what it is like outside. :D

Thanks! It's foggy out here if that makes you feel any better. :)