Note on diamond diffuser panels

[rygh]

I have been using diamond diffuser panels on my LED system to spread out the light.
Those panels are to diffuse flourescent lights. They are flat on one side, and have a rough diamond like pattern on the other.
I put them between LED and screen.

Now I am not so sure it was a great idea!

Our club bought a nice Apogee PAR meter, and I recently did some measurements.
The amount of light lost is huge. It spreads the light out in too wide of a pattern.

Right next to the panel, in line with a big LED cluster, the PAR was about 400.
About 3 inches away, it quickly dropped to 150.
At the screen distance, it was about 90 or so.
That said, it was very uniform at the screen distance. Probably 80-90, very even.
And it was very NON uniform at the LED. Zero to 400.
But still, a 4X drop is not good.

PLUS, keep in mind the reflection off of the water.
As light hits water at a wider angle, it reflects more and more.
At the "maximum angle of incidence", the light reflects 100%, and no light enters.
That angle is roughly about 45 degrees.
So the light coming out at wide angles from the diffuser panel will be completely reflected away.
Thus real PAR is likely far lower than that 90. Perhaps half.

So I am losing a ton of light because of those panels.

[Floyd R Turbo]

I include these on all my scrubbers. The advantage is that using them allows you to place the LEDs very close. Without them, the screens will not start growing nearly as fast, because the LEDs are too intense and disallow initial growth. This was very apparent in my Rev 1 L2s, which had 2 reds with a blue in between them, each 1" apart like this



Almost everyone's screen was bare in the middle, and filled in last. The edges all around the screen filled in first, then in front of the outer reds, and the middle was always last. There would still usually be a bare spot in the dead center of the screen, maybe the size of a penny, even with the diffuser. So I started putting a black dot on the diffuser with a sharpie, and now recommend electrical tape instead as it does not fade.

My current versions have the blues wired in parallel within the series





this reduces the center-burn in significantly, if not all together.

This also allows one to remove the diffuser after the screen is cured / mature.

So all in all, I would have to agree with you that diffusers are not necessary, at least for the long term. My experience has revealed, however, that they are necessary to prevent start-up photoinhibition effects. There is a light intensity level at which algae will not grow - but once algae gets a foothold on the screen, this effect goes away. I can't explain why that is the case - it just is.

My L2 on my personal tank (running just over 5 weeks now) runs with the diffuser on one side and without on the other. I removed one diffuser at the 4 week point, just to see what would happen. Growth was great - no inhibition effects.

If your LEDs are further away from the screen, say 3 or 4 inches, no diffuser should be needed. But, it might still help to even out the light and get a good base going - you would be able to remove it sooner after growth started possibly.

Additional comment: I started recommending to anyone running the Rev 2 versions of my scrubber that they can remove the diffusers after the break-in period.

[rygh]

Good to know!
Never thought about simply removing them later.

Ideal might be to have lots of LEDs running at a lower current. But that is a royal pain to build, and gets expensive.

Just an FYI on another idea I had:
One thing I did on my main tank LEDs was put a short section of PVC pipe around each LED.
It acts a bit like a very cheap reflector tube. I measured that as well, and it made about a 15% difference.
At only 15%, it is probably not worth the effort.
For the main tank it was, since it prevented a light of annoying light-spill out the sides.