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Thread: Reasoning against dual screen builds?

  1. #1

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    Reasoning against dual screen builds?

    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!
    Brandon

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    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.

  3. #3

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    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

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    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.

  5. #5

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    Quote Originally Posted by Bilk View Post
    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.

  6. #6

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    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.
    Brandon

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    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.

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    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

  9. #9

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    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

  10. #10

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    Quote Originally Posted by sabbath View Post
    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.

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