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[APD] PCF Lights for Open Top Tank
Rachel wanted to know if she could use her 220W of PCF lights on her 72
gallon tank without the cover glasses.
This is a good question. I can't answer this completely, but I think
others on the list will be able to.
1) Can the light fixture be used over an open top tank with only a very
small chance of it ever falling into the tank?
2) Is 220W of PCF light 3 inches from the water surface too close?
3) How securely are PCF bulbs installed in an enclosure? Can they fall out?
I think I saw once a picture of a tank with a downward extension at each
end of the light fixture. The extensions looked like stylish legs under a
table and probably hooked onto the two side edges of the upper rim of the
tank. I haven't been able
to locate any of these light fixture supports on the Internet, or the
original picture I saw. Maybe someone gave give us a hyperlink to a picture
of one. Since Rachel said the lights were 3 inches above
the water it leads me to believe that she has this kind of light fixture
enclosure with the extension legs. I think these legs are used to allow
some ventilation of the enclosure which could get too hot from the lights.
Most light enclosures lock onto the top tank rim somehow. Usually the cheap
strip light enclosures have extensions to the sides of the enclosure that
extend down past the outside of the rim. This allows easy centering of the
light fixture (side-to-side) but doesn't really lock the light fixture onto
the tank rim. This is why companies like All-Glass warn users to always use
a cover glass. Without a cover glass, if you lift one side of the light
enclosure, and move the enclosure laterally, the enclosure could fall into
the tank. Tom Barr gave us some pictures of his light enclosures at:
I think the 5th picture of the wood enclosure with the wooden feet, although
exemplifies this problem, or at least the possibility of a problem if the
enclosure is carelessly moved.
However, if the bottom of the legs clamp around _both_ sides of the top of
the tank (either tank trim rim or top of the glass as in Tom's picture) then
I think the chances of having it fall into the tank are greatly reduced.
The bottom of the legs (the feet) would be shaped like an upside down "U".
This would allow the light enclosure to take a good bump at the side and not
pop up and into the tank. Actually I think Tom's design is pretty good
since the wooden legs look like they are rigidly attached to the enclosure.
That stiffens the legs quite a bit, but I would add a little piece of wood
to each of the feet at the bottom to get the upside down "U" shape.
So, Rachel, if your light enclosure has good rigid extension legs that clamp
to the light fixture or tank rim, and can take a sideways bump without
falling into the tank then I would say you can use them with an open top
Another alternative is to build a wooden box exactly like Tom shows (and
many others of us have done), and either put secure legs on it, or hang it
from the ceiling. The total cost of the wood for the box can't be more than
By the way Tom Barr's pictures (# 3 and #4) show a very nice way of
suspending a light box over a tank. I think he used plate glass and either
silicone or epoxy glue. It looks like the base glass is glued to the side
top edges of the tank. The extension legs protrude up from the base glass.
The box is lowered onto the legs, and the legs sort of lock into the inside
of the fixture. I imagine that you would have to lift the box up quite a
bit before it would be free to move laterally. It looks quite secure and
safe. And it is pretty. Hurry up and build one before Tom gets a patent
for it and we have to pay him royalties.
Rachel, if this info doesn't help, describe your light fixture enclosure
more fully, or
refer us to a picture. I'm sure with the expertise on the list we can
figure something out.
Three inches from the water will not hurt as far as
condensation crapping up the bulbs or electrical is concerned. As long as
you don't have any turbulence at the water surface. (Remember, with an open
top tank turbulence will also dissipate CO2.) Without any spray, the bulbs
and electrical should stay dry as long as you have decent ventilation in the
room, and have a decent HVAC system. Since the tank is open top you should
have enough ventilation at the water surface to prevent any condensation. I
would make sure the light enclosure has a ventilation opening at the top of
it to allow flow through ventilation. I don't think fish bumping into a
bulb would ever get hurt. It is better they do this than land on the floor!
Actually the more emersed growth in the tank made possible by the open top,
the less the fish will want to jump.
So if you think the lights are secure enough, try it. You can always go
However, splashing from fish could wet the bulbs or electrical contacts.
Considering this and the fact you may have too much light without the cover
glass, I would personally feel better with having 6 inches between the bulbs
and water. I have experience with this setup with my six 40 Watt 48 inch
fluorescent tubes enclosure. I have never had a problem with it at 6 inch
height. I'll bet this would give you a problem though as those extension
legs are probably not adjustable.
An advantage of hanging the light box from the ceiling is that you can raise
the box higher when you want to reduce the light or do some heavy duty work
inside the tank.
My 48" T15s are very snugly installed in their end sockets. Not like those
flimsy light strips where when you flex the enclosure, the tubes pop out. I
don't know how PCF lights are installed. I think the plug end is secure,
but if the bulbs are just retained by "C" spring clips they may have to be
retained better so they don't fall out. Any comments?
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