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Old 07-05-2013, 02:47 PM   #31
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Read the thread I posted. It goes into detail about this exact topic. My PAR meter shows the opposite. What does your PAR meter show with just blues then just whites Mr_X? I know you have a meter too. Understanding you probably have more blue emitters than white. I grew lots of coral with just MH before actinics became popular. PUR would be a better number for comparison, but I am unsure how to get a PUR reading from my meter.

Lumen for lumen, corals do use a lot of blue light. But they use other frequencies as well. But at white frequencies, nuisance algae has an advantage and your corals will grow fast but be browner.

Here's another thread:

http://www.nano-reef.com/topic/65551...ely-aesthetic/

It's a good topic as there is some different opinions.
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Old 07-05-2013, 08:59 PM   #32
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Quote:
Originally Posted by Gregcoyote View Post
Read the thread I posted. It goes into detail about this exact topic. My PAR meter shows the opposite. What does your PAR meter show with just blues then just whites Mr_X? I know you have a meter too. Understanding you probably have more blue emitters than white. I grew lots of coral with just MH before actinics became popular. PUR would be a better number for comparison, but I am unsure how to get a PUR reading from my meter.

Lumen for lumen, corals do use a lot of blue light. But they use other frequencies as well. But at white frequencies, nuisance algae has an advantage and your corals will grow fast but be browner.

Here's another thread:

Actinic purely aesthetic?? - Lighting Forum - Nano-Reef.com Forums

It's a good topic as there is some different opinions.
I notice there are some confusions on that link. When we talk about PAR (Photosynthetically Available Radiation) it is the total radiation generated by the light source with wavelength between 350 to 750 nm (actinic blue to red). If you look at the spectrograph of a lighting fixture you will notice a certain wavelength is more pronounced than the rests. The PAR is the total emission of light coming from that fixture while the PUR (Photosynthetically Usable Radiation) is the specific wavelength of that light being absorbed by a specific corals we are dealing with. Keep in mind that different types of corals prefer different wavelengths (colors) or combination of colors. What that means is that the PUR depends on which corals you have in your tank. Some corals prefers more actinic and some prefers combinations of colors from blue to red. Now lets consider a pure actinic light. Its spectrograph will emphasize the blue which is the shorter wavelength. If your corals prefer the blue then your PUR is almost equal to PAR. The PUR can only be less or equal to PAR.
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Old 07-06-2013, 11:39 AM   #33
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On my straight blue and white unit, The PAR coming from the blue at "X" distance was 100, while just the whites, was 72. I have been growing assorted corals just under the blues in one of my tanks for some time now. Decent growth and coloration, but less than the main tank with both on at 100%. FYI, I have montipora a little further away than "X", and don't use the whites at all in this tank. PUR must be much higher than PAR in this case, or would it be safe to assume that montipora does well under less than 100 PAR?
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Old 07-06-2013, 11:58 AM   #34
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As I have mentioned, PAR is the total reading of the lighting fixture radiated into a particular space in the tank. It includes all the colors or wavelengths within the spectrum coming out from the fixture available for photosynthetic life including plants and corals. While PUR is the colors on that PAR where the corals utilize for photosynthesis. It only follows that PUR can never be more than PAR given same fixture.
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Old 07-06-2013, 01:48 PM   #35
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On my straight blue and white unit, The PAR coming from the blue at "X" distance was 100, while just the whites, was 72. I have been growing assorted corals just under the blues in one of my tanks for some time now. Decent growth and coloration, but less than the main tank with both on at 100%. FYI, I have montipora a little further away than "X", and don't use the whites at all in this tank. PUR must be much higher than PAR in this case, or would it be safe to assume that montipora does well under less than 100 PAR?
Don't you have a 2:1 ratio of blues to whites?
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Old 07-06-2013, 02:02 PM   #36
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No. 30 and 25.
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Old 07-06-2013, 02:27 PM   #37
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Some monti's do fine at 100 par. I would agree that pur is never greater than par. It is the depth the coral lives at that controls the color "tuning" of its algae. Deeper the bluer it is. And par is a broad measurement of all light frequencies, so different corals will see a different pur value from the same light. Royal blue led emitters are quite a bit different than a actinic fluorescent. Never had much luck growing anything under just actinics.
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Old 07-06-2013, 02:53 PM   #38
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Corals that are found in deeper water like mushrooms love the actinic or blue, while those corals in shallow water prefers the white sunlight. This would explain why some reefers are having problems. They wonder why some of their corals are doing fine and some are not. It is the balancing of these colors. It is true that each type of coral would receive different PUR from same light because each variety select certain wavelengths or colors. It is like the food animals eat. Your pet dog prefers only a certain brand and they will not touch any other food. The food is the PAR and the brand is the PUR.
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Old 07-06-2013, 08:24 PM   #39
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Not true. No corals prefer white light over blue, they just prefer more or less PAR. They don't know what color the light is.
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Old 07-06-2013, 09:34 PM   #40
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Here is an article that I think is also helpful:

(http://saltaquarium.about.com/od/lig...eef-Lights.htm)

I think I am understanding all of this. From what I am hearing PAR is the total light given while every coral has a specific need/requirement of usable light (PUR). Intensity is only a part of the lighting requirements while color from the lighting is also very important. The article sums it well with the A B and C points on the spectrum.
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