Reasoning against dual screen builds?

[realtime3d]

Hey all,
I know the typical recommendation is for a single screen lit by both sides. What are the downsides of two screens with a small gap between the two lit by the same lighting configuration? My question stems from being able to clean screens on alternating weeks and allowing penetrating light to benefit the opposing side especially after cleaning when most light penetrates through anyways. Thanks!

[Floyd R Turbo]

The downside is that you think you are getting twice the action, but you are actually getting half. If you take the example of a T5HO or CFL lamp, one on each side of a screen with a good reflector, the light from each lamp is getting more or less fully re-directed toward the screen. So light that emanates radially from the lamp is re-directed in one direction.

Now take that same 2 lamps (for simplicity, we will discuss only the T5HO linear lamp) and put it between 2 screens. Now you have less than half of the total output of each lamp being directed on one screen, less than half to the other screen, with the remainder lost to the sides. Even if you made some kind of split reflector to be placed along the edge of the lamp that trapped and re-directed this sideways-travelling light, you are still splitting the light source 50% in one direction, 50% in the other. The result of 50% of 2 lamps split between 2 screens is the exact same effect as if you had placed one lamp on each side an directed 100% of the light to the screen. the difference is that in the former, you have 2 single-sided screens, which are less efficient than double-sided screens because the roots die quicker due to shading.

Now that's all related to waterfall scrubbers. UAS might work OK as far as the shading issue goes, but you are still not really gaining anything beside being able to clean the screens at different times, which you can do with a single sided (WAS or UAS) as well by just slicing the screen vertically into 2 parts.

[Bilk]

Bud I don't understand your explanation. How would the light be reduced? The same lamp is illuminating just one side as it would on a dual sided scrubber. Not sure I understand.

Yes good timing LOL

[Floyd R Turbo]

If you do not have a split-reflector to direct 50% of the light in one direction and 50% of the light in the other direction, then inherently you will lose light sideways from the lamp, reducing the overall effective output of the lamp on the screen.

A normal reflector 'pushes' all the light in one direction. You would have to DIY a reflector that would be like 1/2 of a reflector, like a 1/4 circle, with another 1/4 circle attached to it, like a "V" except curved (hard to describe), then you would have one of these along each side of the lamp (somehow) in order to capture the sideways-travelling light and direct it forward.

[sabbath]

Bud I don't understand your explanation. How would the light be reduced? The same lamp is illuminating just one side as it would on a dual sided scrubber. Not sure I understand.

Yes good timing LOL

Because a good reflector will reflect most of the light on the back side of the lamp back to the front.

[realtime3d]

Thanks for the response. I am not expecting 2x the performance nor major volumetric lighting improvements. The lighting is LED based which is inherently hemispherical. I was fishing for something detrimental to a dual screen build. In my specific situation, my scrubbers are short and wide (5x17) but flowing a lot of water. The inlet is horizontally mounted entering on one side but the 3/4" pipe consumes a sizable portion of that 5". To try and squeeze out a little more sq. in., I have the pipe inverted so the water exits at the top and rolls down the sides. So in effect, the pipe is at the same level as the top of the screen(s). Since water flows down both sides of the pipe, I have screens leaning against each side of the pipe. This leads to my dual screen build question I mentioned. I wanted to make sure there wasn't something inherently bad -- roots or strands that decay or something. I'll post some picture when I get home for clarity.

[SantaMonica]

1-sided has half the filtering of 2-sided, even with the same wattage, because with 1-sided the roots die twice as fast from darkness.

[Bilk]

I'm still confused, but that's normal. In a double sided configuration one lamp illuminates one side of the screen and the other lamp the other side of the screen. I guess there's some light that goes thru and then reflects back again from the reflector on the opposite side, but that's only until the algae starts to fill the screen.

I guess the way I view this is just two single sided scrubbers which afaik are also suitable, aren't they? I mean this is my understanding of how I see the system working. Same light output, same screen size each side, just two screens instead of one. Again, maybe I'm confused LOL

[Bilk]

So if you have half the scrubbing ability with one screen, then double it, you have the same scrubbing ability as a double-sided scrubber. .5+.5=1

I also think there's still a way to make this work if light penetration to the roots is an issue. Just place lights on either end so the screen is illuminated from four sides.

I guess the only reason I saw benefit to two screens started alternately, is there's less down time as one screen half filled will still have more capacity than one screen cleaned. Again, I must be confused :)

[Bilk]

Because a good reflector will reflect most of the light on the back side of the lamp back to the front.
Doesn't this only occur for the time there's no algae growing on the screen? Once it starts to fill with algae that reflected light is greatly diminished. That's why you need a light on both sides to begin with or just one light and a reflector would work.

[Floyd R Turbo]

1-sided has half the filtering of 2-sided, even with the same wattage, because with 1-sided the roots die twice as fast from darkness.

^^ this snuck in above one of your posts

One lamp, one reflector, light reflects forward. Reflection off the opposing reflector has no factor at all.

[Floyd R Turbo]

I also think there's still a way to make this work if light penetration to the roots is an issue. Just place lights on either end so the screen is illuminated from four sides.

If you are referring to edge-lighting the screen, no, that won't work. Light must be perpendicular to the growth substrate.

[realtime3d]

If that were the case, we'd only have algae on the bottom of the aquarium versus the sides. Light scattering, reflection and refraction virtually guarantee something hits the substrate perpendicularly.

[Bilk]

I'm new to ATS in employing one, however I've seen them at work and have read about them for years as most of us have. There's a few things I'm not convinced of though. Roots dying is one. If the screen is filling from both sides with algae, the illumination from both sides, the light reaching the "roots", is continually diminishing on each side as the light get's blocked anyway. As for edge lighting, I don't believe that the light source has to be perpendicular as a secondary source. Light is light. It radiates and by definition that isn't a linear aspect.

I can see a scrubber where the screens are separated by two or three inches and have a few on the edge and pointed in between the screens to help with the "dying root" issue. The back of these screens aren't the primary growing medium. The front is. The edge light will not be wasted. It's still energy into the system. Heck if the entire inside of the scrubber were made of reflective material, you could probably get growth on both sides of both screens.

I guess there's only one way to find out :) Maybe I'll patent it :)

[Bilk]

If that were the case, we'd only have algae on the bottom of the aquarium versus the sides. Light scattering, reflection and refraction virtually guarantee something hits the substrate perpendicularly.
Exactly! :)

[Floyd R Turbo]

If that were the case, we'd only have algae on the bottom of the aquarium versus the sides. Light scattering, reflection and refraction virtually guarantee something hits the substrate perpendicularly.

Maybe in your aquarium. But not on a scrubber.

[Garf]

I've thought about edge lighting. Even tested it. Shine a light through the edge, and the whole screen glows (while being shaded from the light source).The light travels through the screen material.This would give light to the inside layers, but if it's enough or not, only testing it would confirm. However, plumped for the one sided screen cleanings.

[Floyd R Turbo]

I'm new to ATS in employing one, however I've seen them at work and have read about them for years as most of us have. There's a few things I'm not convinced of though. Roots dying is one. If the screen is filling from both sides with algae, the illumination from both sides, the light reaching the "roots", is continually diminishing on each side as the light get's blocked anyway. As for edge lighting, I don't believe that the light source has to be perpendicular as a secondary source. Light is light. It radiates and by definition that isn't a linear aspect.

I can see a scrubber where the screens are separated by two or three inches and have a few on the edge and pointed in between the screens to help with the "dying root" issue. The back of these screens aren't the primary growing medium. The front is. The edge light will not be wasted. It's still energy into the system. Heck if the entire inside of the scrubber were made of reflective material, you could probably get growth on both sides of both screens.

I guess there's only one way to find out :) Maybe I'll patent it :)

Yes, roots die in double-lit screens as well. They just don't die as fast, because though it may seem like an inconsequential amount of light that penetrates from one side to the other, when light is penetrating from both sides to the roots, they will last a few more days before the dying process starts versus a single sided screen. Thickness of growth is also a factor in all cases.

Again, edge lighting really does nothing. You cannot force light to illuminate the substrate/roots from the edge. It would only penetrate a little ways along the substrate, then it would be absorbed or reflected. I'm really having a hard time understanding why you think this is feasible. I'm not trying to be a jack--- here, just honest. People have had troubles solved by changing the light orientation from a 60 degree angle to the screen to a 90 degree angle. So why would going the other direction help anything?

[Floyd R Turbo]

I've thought about edge lighting. Even tested it. Shine a light through the edge, and the whole screen glows (while being shaded from the light source).The light travels through the screen material.This would give light to the inside layers, but if it's enough or not, only testing it would confirm. However, plumped for the one sided screen cleanings.

So are you saying you tried it and it worked?

[Garf]

In as much as the screen material glowed, yes. Didn't try it with algae on though because this sets up another load of obstacles, stopping algea growing on the edge of the screen, concentrating light to illuminate he screen material and waterproofing the light source are just a few I can think of at the minute. One sided cleaning is much easier to sort out and test.

[Bilk]

1-sided has half the filtering of 2-sided, even with the same wattage, because with 1-sided the roots die twice as fast from darkness.

I actually don 't see the difference between incorporating two screens back to back in one unit vs THIS (http://www.santa-monica.cc/Hang-On-Glass-HOG-Upflow-Algae-Scrubber-UAS--05-Cubes-feeding-per-day--MAGNET-VERSION_p_21.html) :)

This part, in particular, applies to the discussion:


The number of gallons or liters of water does not matter. If you feed more than this, you can get multiple units; multiple units are preferred because you can clean one per week, and because you'll always have one filtering while the other starts growing again after a cleaning. * emphasis added by me :)

So here we have a single sided unit and you suggest that people should purchase multiple units for the same reason the OP suggested and I suggested (in another thread), to keep scrubbing action working in the system after one screen is cleaned so the bioload absorption doesn't fluctuate too much.

So which is it?

[SantaMonica]

I guess there's some light that goes thru and then reflects back again from the reflector on the opposite side

That's the definition of a 2-sided screen: Light and flow goes through it.


but that's only until the algae starts to fill the screen.

That's all the time it takes for the roots to die.

[Floyd R Turbo]

There is no difference. Like I said, you can do what you suggested, having back-to-back screens, alternating cleaning, or you can get 2 single sided HOGs and alternate. It makes no difference in those 2 scenarios, because in both examples, they are single sided. The only difficulty becomes placing a light source in between the 2 screens and protecting it. This is more difficult to perform as a UAS as you can imagine.

I was saying the difference would be if you ran a double-sided scrubber of the same size (same LxW as one of the single screens), which had 2 screen sections (but in half vertically), and you alternated cleaning those. Because it's double-sided, it is inherently better, no matter if it's UAS or waterfall, with half of the total LxW.

The difference between a dual-single-sided screen scrubber and a single double-sided screen scrubber is that in order to "equal" the scrubbing power, you need 2 single sided screens, each one of them being the same size as the double-sided screen. Because you need the same physical growth area - if your single sided screen was 4x6, then you have 24 sq in of growth area. Your double-sided screen has 24 sq in of growth area on each side. I say "equal" because as discussed, single sided screens are less than half as powerful as a double sided screen when both are properly sized (i.e. the single sided screen is twice the LxW of the double sided one, with the same amount of light, all on one side)

[realtime3d]

I wasn't trying to start a war as I've been following SM, Floyd and others' posts over the past year. I was only hoping to kindle some discussion. As I think I stated earlier, my goal was to reclaim some lost surface area because of the 3/4" drain pipe eating into my 5" vertical clearance. Either way, I thought I'd throw up some photos of the build that's still a WIP. They've been running about 2 weeks with one screen being cleaned a week ago. I get decent growth for its age but need to diffuse some of the LED light because of close proximity to the screen itself. You can also see the bubbles on the left side from the Durso I mentioned in Rygh's Gen4 build thread. Comments and suggestions welcome! Thanks again for everything this site's contributed to scrubber evolution.
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[Bilk]

War? Hope my comments and questions weren't taken that way. It's just a discussion of what practices work and how they may be improved or why certain things don't. I find there's a lot of information to be gathered here. I'm really looking forward to utilizing an ATS on my system.

[Bilk]

Just to add, I may order some specular mylar to include in my build as the leds I have do not have reflectors. They have a built in heat sink though and don't require additional cooling. It's why I chose them. Don't want more fans (more noise) added to things. These leds are used for signage to replace neon or in lieu of neon. I may need to add some blues though. They have multi-color pucks and might be a good option as well. I think they'll work just fine.

[Floyd R Turbo]

I didn't mean it to sound like a war either - just trying to disseminate information, sometimes it does tend to sound a bit heated.

mylar may or may not help with LEDs, since they are directional. These signage LEDs are likely still directional also, if they are the ones I am thinking of (the little squares with 4 LEDs?) so you probably don't need any reflectors. 90% of the light is thrown forward in a cone, the only light you see from the side is really negligible. LED intensity is much higher, so there is much less need to gather the small percentage of stray light and direct it forward. However if you place the array far away, a cone or tube of mylar might help. But for the really low power LEDs, you want those pretty much right against the screen (for <1W LEDs) and tightly packed so this is not an issue.