[Coral-List] RE: Coral-List Digest, Vol 31, Issue 31 What is PAR?

Jason Licamele jasonlicamele at hotmail.com
Tue Jan 24 22:03:05 EST 2006

P.A.R. is Photosynthetically Active Radiation which unit of measurement is:

meter^2 second^2    (mol m^-2 s^-2)

It is not a percentage but a unit of displacement over time of photon 
molecules.The appropriate unit for discussing photosynthesis is referred to 
as Photosynthetic Photon Flux (PPF) which is measured in mol m^-2 s^2.   
P.A.R.  ranges between 400 - 700 nm.

Lumen is derived from illumination which is determined with the human eye 
(or lux meter) and is usually referred to as lux (lx). The human eye is 
capable of adjusting to light quickly and is not an accurate measure of 
light (radiation of an electromagnetic wave with wavelengths in a range of 
1nm to 1mm). Plant Scientists refer to PAR rather than Lux.

I assume you are using the bulbs for some type of algal / coral system. 
Theoretically bulbs with the same lumen will have the same PAR. However to 
be completely accurate (due to variation in manufacturing) a measurement of 
PAR should be taken.



Jason D. Licamele
Environmental Research Laboratory
Soil, Water & Environmental Science
Agriculture and Biosystems Engineering
University of Arizona

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>Subject: Coral-List Digest, Vol 31, Issue 31
>Date: Tue, 24 Jan 2006 12:00:16 -0500 (EST)
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>    1. Photosynthetically Active Radiation (Jade Maggs)
>Message: 1
>Date: Tue, 24 Jan 2006 11:57:56 +0200
>From: "Jade Maggs" <jmaggs at seaworld.org.za>
>Subject: [Coral-List] Photosynthetically Active Radiation
>To: "Coral List Server" <coral-list at coral.aoml.noaa.gov>
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>Please can someone explain what P.A.R. is. I gather it is a percentage of 
>lux which is photosynthetically active. For two bulbs with the same lumen 
>output, can P.A.R. differ.
>Jade Maggs
>uShaka Marine World
>083 515 1079
>Coral-List mailing list
>Coral-List at coral.aoml.noaa.gov
>End of Coral-List Digest, Vol 31, Issue 31

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