Actinic Led

[mr_X]

And I love a good debate! Thanks guys.

 

[jeffaquarius]

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.

 

[Gregcoyote]

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 .

 

[jeffaquarius]

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.

 

[Gregcoyote]

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.

 

[jeffaquarius]

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.

 

[mr_X]

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.

 

[Gregcoyote]

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.

 

[jeffaquarius]

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?

 

[Gregcoyote]

Good question. Need to research that point.

 

[mr_X]

I'm using straight blue LEDs over various corals right now, and they are all doing very well and are quite colorful. I don't have anything blue in there though, but it's mainly because the only blue corals I have are acropora and I'm not running enough blues over this tank to support them. Maybe I'll lower the fixture and toss in something.

 

[jeffaquarius]

Being curious of my own question, I searched and i found this link.
Small Polyp Stony Coral and Light Wavelengths - Are LEDs 'Reef Capable'? You decide.

This is a quote from that link

"Montipora caprricornus and Montipora digitata are of the same genus, but are two different species. These two corals do not grow at the same rate, when under the same photosynthetic wavelength of light. Each species requires a specific color wavelength (measured in nanometers) to obtain “optimal” color pigment of the coral’s tissue. "

 

[mr_X]

If that's the case, then it's safe to say that the units over my tank are not as limited in terms of wavelengths as we thought.

 

[Gregcoyote]

Again, I think you can see it in terms of bandwidth. The spectrum narrows from blue to black the deeper you go. The corals algae evolve to absorb those frequencies, down to darkness where only filter feeders live and there is no photosynthesis. But why would a coral be blue if it was evolved to absorb blue light ? Because of variation, I can see how a coral might use whatever it can get to grow. And LEDs, even blue ones have a pretty wide bandwidth in the blue spectrum. They aren't like lasers which are very monochromatic. That was my big word for the evening. Thank you and good night. Zzzz

Another pretty good read;

http://www.reeffrontiers.com/content/40-how-lighting-effects-corals.html

 

[jeffaquarius]

Very interesting to note that corals can absorb different wavelengths and create a distinct color for itself. IMO the pigmentation of each specie could be some sort of a defense mechanism for survival to repel other sea creatures from consuming it just like how octopus with a more sophisticated comouflage. The blue corals could be too sensitive for UVa or UVb but all we see is just blue. It must be absorbing other colors to tint itselft with blue.