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Old 07-07-2013, 07:42 PM   #61
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And I love a good debate! Thanks guys.
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Old 07-07-2013, 08:46 PM   #62
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I agree and the rest of the readers may have picked up more info from both sides. Just a quick note though. You often refer to PAR when we know that PUR is responsible for photosynthesis for corals. PAR is a broad term for all photosynthetic life which includes wide range of colors while PUR is specific.
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Old 07-07-2013, 09:12 PM   #63
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I agree and the rest of the readers may have picked up more info from both sides. Just a quick note though. You often refer to PAR when we know that PUR is responsible for photosynthesis for corals. PAR is a broad term for all photosynthetic life which includes wide range of colors while PUR is specific.
Because each coral species has a PUR number, we are almost forced to use PAR for simplicity .
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Old 07-07-2013, 09:30 PM   #64
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The way I understand PUR is that it is the intensity of a specific frequency (wavelength or color) or is it the minimum PAR the coral requires? Please correct me if I am wrong.
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Old 07-07-2013, 11:14 PM   #65
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The part to note is "active" vs "usable."


PAR is the value that weights the amount of light a emitter outputs at all frequencies that can cause photosynthesis. While lumens are the light output period. PUR is the amount of light an organism needs at certain frequencies that will cause photosynthesis. This can be almost anything in the visible spectrum. Tomatoes like one frequency, or set of frequencies, while deep water corals symbiotic algae adapt to a much narrower bandwidth. Green plants are green because they absorb all frequencies but green. That gets reflected back to your eye. Corals work the same way. That's why hydroponic led lights aren't green, they are the color opposite on the color wheel, magenta. That is the frequency of maximum absorption for a green plant. So the PUR of that plant would be in the magenta frequencies.

Of interest, green plants look black under magenta LEDs as I have in my algae scrubber, indicating little light is being reflected back but being absorbed in the plant tissues.
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Old 07-08-2013, 01:25 PM   #66
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Yes that is exactly how I understand both PAR and PUR. Corals PUR could be on the shorter wavelength of the spectrum but not necessarily of exactly same frequencies.
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Old 07-08-2013, 04:39 PM   #67
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I believe a color temp that works for one coral, will work for all corals. You just need to turn up or down the intensity.
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Old 07-08-2013, 05:04 PM   #68
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I believe a color temp that works for one coral, will work for all corals. You just need to turn up or down the intensity.
In general that would be true, but corals that grow in shallow water have evolved to accept a broader bandwidth of light they can use for photosynthesis, while deep water corals exist on higher frequency blue light alone for photosynthesis. Both can grow under blue light just fine, making your point. But you lose so much color under just blues. Maybe okay for growth, but not display IMO.
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Old 07-08-2013, 10:15 PM   #69
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If it is true that all corals would have the same reaction to the same wavelength supposedly blue for photosynthesis, why would there be different colors of corals? What happens to corals with blue color? It would certainly reflect the blue and absorb other colors. By doing so, is it not that it would hinder its growth by not absorbing the blue?
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Old 07-08-2013, 11:09 PM   #70
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Good question. Need to research that point.
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