LEDs, why 660nm reds?

[Fredfish]

I'm starting this thread so as not to hijack the thread I originally posted it in.

I got two answers that puzzle me somewhat.

The first is that this is one of the peak absorption spectra of chlorophyll a.

OK, but most corals never see that spectrum. The maximum penetration of 650 nm is about 8 or 9 meters. The maximum penetration of 600nm is 15 meters (found a nice chart earlier, but can't find it now). 10 meters is where the shallow fore reef starts. In my limited diving experience, this is where the highest diversity of corals starts and 15 meters is right in the middle of the fore reef.

To me, this spectrum is not required by most corals.

The second answer was for looks, light the coral reflects back. From articles I have read in the Advanced Aquarist, for reflection and fluorescence, we should be looking at light in the 580 to 625 nm range. There is also absorption going on in this range.

I would think that if you want to include red spectrum in an LED light, you would get more value out of reds in teh 580 to 625 nm range.

What am I missing?

[Khemul]

The thing about the 580 to 625 range is that most LED fixtures use white LEDs. The white LEDs have a peak in the mid 500s and then slope quickly downwards into the 600s.

Since the common suggestion has shifted from cool white to neutral or warm white LEDs, the peak is bigger and thus usually covers 580 to 625 pretty well. A cool white fixture may get some benefit out of a red or amber supplement. Deep red isn't necessarily lacking, but may need supplementation on a neutral white setup. Haven't tried warm white, but in theory they should cover even 660. Similar concept as cyan/blue being supplemented. It's there, but may be overshadowed/underpowered compared to the other spectrums put out.


As for what is useful to the corals, there is a lot of debate there. But as far as I've seen, and it is heavily dependent on type of coral (I managed to grow Kenya Trees under a couple eBay 9W cool white par20 bulbs perfectly fine in the past), the corals would be perfectly happy with a violet/royal blue/blue setup. The rest is mainly for our benefit.

[Jerzey]

i have two 660 nm deep reds in my fixture that i'm swapping out with 430 nm hyper violet... i've herd alot about reds causing more then usual algae growth and from experience can now say it's true (no3-5 po4-0)... it only seemed to grow where there was just a little less flow then anywhere else in my DT and i have high flow with my BB.... NW have more then enough of that spectrum that it really doesn't have to be targeted unless you really want to... i'm more concerned with the 410-500 nm wavelengths now and gonna see if i notice a change in my corals

[Fredfish]

I think I found my answer in starting to re-read the Open Letter to the Lighting Industry thread.

So, it appears that some red above 600 is needed to make the eyes happy...

http://reefcentral.com/forums/showpost.php?p=21734372&postcount=21

Sigh, I'm getting old.