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Re: How much light is reflected by a glass cover?

On the topic of glass, there are a lot of options including the more
expensive optical glass:



I often find good deals on optical glass surplus items here:

I know we're now moving into the more expensive areas and it's probably more
economic to just increase your lighting than buy optical glass but every now
and then you can get lucky on eBay or Hydroponics retailers and find
something useful. I don't remember the name of the product but I used some
plastic optical film a while ago for a project and it was relatively cheap,
durable and close to optical grade glass. I've been told plexiglass has
better light transmission properties than soda-lime glass but I have never
used it for optics. I'm sure there are plastic alternatives to glass that
are probably better than our standard lids however you will always need to
keep them nice and clean, I find my glass lids get dirty on a daily basis
from evaporation and keeping them clean is a pain but important. Perhaps
finding a net or mesh as you said might be better, you can get one kind at
fishing stores which is made of thin fishing line, shouldn't be toxic and
will probably allow more light to pass than thicker or non-trasparent
materials. Do they make trasparent fly screens?

Good luck
Giancarlo Podio

----- Original Message -----
  a.. To: aquatic-plants at actwin_com
  b.. Subject: Re: How much light is reflected by a glass cover?
  c.. From: Bill Wichers <billw at waveform_net>
  d.. Date: Tue, 25 Feb 2003 12:53:58 -0500


> >All told, I expect a clean cover glass to waste maybe 25% of the useful
> >energy, so it is pretty significant. [Unfortunately, my fish are all
> >killies, and air just doesn't keep them in the tanks. :-)]

There is a special glass known as "starfire" glass that is much clearer
than the usual soda-lime (greenish) glass. I'm not sure what the exact
spectral transmission properties are, but it certainly appears to allow
much more light to pass through. If the glass is a big problem in your
setup you might check with a glass shop to see if you can get some 1/8" or
so starfire glass panes to use in your lights.

>I wonder if a wire mesh would be a better option. I've been thinking
>about removing the glass but two things bother me[using powercompact

Use fiberglass mesh -- it will last longer in a high-humidity environment.
Aluminum WILL corrode over time if it is constantly misted with water,
especially if that water has any salt or similar compounds in it. Ask
anyone along a coast how long aluminum lasts in the salt spray and you'll
see why this is a concern

Steel mesh is usually hot dip galvanized, and you don't want the zinc run
off getting into your tank. Zinc strips are often installed at the peak of
roofs so that the runoff prevents algae and moss growth on the shingles to
take advantage of this -- zinc is toxic!

If you need the mesh to handle high heat then Al is probably your only
option, but I'd try to use fiberglass if at all possible.

>1) Water splashing on hot tubes could cause failure.

Not usually a problem if your lights are suspended high enough above your
tank, but this will depend on your particular setup.

>2) Strip light accidentally getting knocked into the tank.

Any fixture dropped into the tank will be a problem, with or without a
cover glass. I have had success building "springy brackets" to allow me to
snap little 13w PCF fixtures into the rim around AGA tanks, but I've never
tried it with anything larger than the AH Supply 13w PCF fixtures. For any
open-top tank I recommend secure light mountings AND a GFCI to help prevent
a dropped fixture from becoming a big problem.

BTW, those "springy bracket" fixtures use no cover glass, and hold the bulb
about maybe 5-6" above the water surface. Even with a bit of mist coming
from the air-driven filters in those tanks, I haven't had any bulb breakage
and the reflectors only need occasional cleaning to wipe off the mineral
deposits. I've been running the lights for about 3 years now this way.


Waveform Technology
UNIX Systems Administrator