par readings

[jason401]

i have been searching for a good reading on par readings..all the info on it...anyone know of any good links?
tia,

 

[inverted]

What do you want to know specifically? Light and PAR is a complicated topic. Well, PAR is pretty simply, it is basically just the amount of light between 400-700nm hitting a given area over a given time (actually, per unit area is called "ppfd", but PAR and ppfd are mostly interchangeable for hobby speak anyways). Usually, outside of the hobby, we "weight" light to compensate for sensitivity of our eyes. So, light, in the lighting industry is given by lumens (or lux - same thing just per unit area). Lux and lumens are sort of like PAR and ppfd, they are light between 400-700nm, but lux/lumens are weighted to the human eyes sensitivity; for example, our eyes are approx 20 times more sensitive to yellow/green light than blue or red light, but blue light may be better for corals... so, lux/lumens are not useful for us (some use them anyways because they are convenient and/or they apparently don't understand what a weighted metric is or something...)

If you want more depth than that
Sanjay Joshi's facts of light pats 1-4 are a good into:
Part 1: What is Light? - http://www.reefkeeping.com/issues/2006-02/sj/index.php) by Sanjay Joshi

Part 2: Photons - http://www.reefkeeping.com/issues/2006-03/sj/index.php

Part 3: Making Sense of Light Measures - http://www.reefkeeping.com/issues/2006-04/sj/index.php

Part 4: Color Temperature - http://www.reefkeeping.com/issues/2006-05/sj/index.php

Also, Sanjay's PAR reading website is popular for comparing lights (remember the PAR readings for halides listed here are without a reflector - PAR is light over a given area, so, focusing the light with a reflector can multiply par by many times).

Dana Riddle also has lots of good articles on PAR

How much light? - (pay attention to table 1 at the bottom too) http://www.advancedaquarist.com/2007/3/aafeature1

Spectrum or Intensity? - http://www.advancedaquarist.com/2002/2/aafeature

The Best Lamp is? - http://www.advancedaquarist.com/2008/12/aafeature1

He has too many to list, but many can be found here: http://www.advancedaquarist.com/search?sort_order=ascending&b_start:int=0&Subject:list=Dana Riddle

His coral coloration articles are really good.

 

[jason401]

thanks inverted...im gonna get my read on..