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Re: [APD] Plexi lid vs. Glass

Have you by chance measure the absorption of red and blue in water column?. 
It is significant for the typical tank depth?.



>From: Wright Huntley <whuntley at verizon_net>
>Reply-To: aquatic plants digest <aquatic-plants at actwin_com>
>To: aquatic-plants at actwin_com
>Subject: Re: [APD] Plexi lid vs. Glass
>Date: Wed, 21 Sep 2005 06:07:44 -0700
>First surface reflections are almost the same from glass and plexi
>(about 4% for each surface), but plexi does absorb less, particular of
>the important red light. Glass can absorb up to 10-15% of that in 1/4"
>thick panels. I have measured it. [Notice how green the edges look?
>That's because most red has been absorbed and only blue-green propagates
>the long way through it.]
>Unfortunately, the warpage in plexi (acrylic) is not from lamp heat, but
>from absorbing water and swelling. When that happens on one side, it
>results in truly impressive bowing. [It also melts at very low
>temperatures, so lamp heat isn't a minor issue if an end moves up
>against a hot tube.]
>There are other good glazing plastics, like Lexan (expen$ive) that do
>not bow, but avoid plexi unless you are willing to cement on ribs to
>resist the warping. Those will, of course block and scatter more light.
>Check out polyester and polycarbonate.
>You may find that "water-white" glass, the "Pyrex"-like stuff, is the
>toughest and most economical material for covers. It is nearly as clear
>as plexi and much more durable and cleanable(if unbroken). Ask your
>local glass shop.
> >Message: 2
> >Date: Tue, 20 Sep 2005 14:43:30 -0400
> >From: "David Grim" <grim1214 at bellsouth_net>
> >Subject: Re: [APD] Plexi lid vs. Glass
> >To: "Aquatic Plants Mailing List" <aquatic-plants at actwin_com>
> >
> >(snip)
> >Hi, you guys have been discussing how much light is lost through glass. 
> >is good to know. Anyone know if more or less is lost through a 0.25 inch
> >piece of plexi from Home Depot? I friend of mine added this to his tank 
> >I was considering doing
> >it also. I have so much evaporation with an open top.
> >Thanks,
> >Kelleen Harris
> >(snip)
> >
> >The main issue using plexiglass for tank tops is warpage of the plexi, I 
> >assuming from the heat of the light. This from previous threads on this
> >subject.
> >
> >Regards,
> >Dave
> >
>Wright Huntley - Rt. 001 Box K36, Bishop CA 93514 - whuntley at verizon_net - 
>760 872-3995
>"...watching Mayor Nagin and Governor Blanco handle the New Orleans/ 
>Louisiana debacle is like watching Moe and Curly trying to work a Rubik?s 
>Doug Giles
>Aquatic-Plants mailing list
>Aquatic-Plants at actwin_com

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