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Re: Need for Fans in Light Fixtures

Roger Gordon wrote:

> My wife has used a 48 inch Phaser IV for several years that utilizes
> four
> T-8 bulbs.  Not the same as with power compacts, but she has been
> very
> pleased with it over her 55 gallon tank.  Her plants grow very
> nicely.  The
> fixture does not get very warm even after being on all day.
> With respect to your comment that the lack of a cooling fan may be
> not be a
> good idea, it all depends.  A properly engineered lighting fixture,
> whether
> it uses fluorescents, power compacts, or metal halides does not need
> a
> cooling fan to maintain optimal operating temperatures.  My wife's
> Phaser IV
> is a case in point, as are the fixtures made by Aqualine Buschke and
> Giesemann.  Of course, good engineering is not cheap, which is one
> reason
> the fanless fixtures cost so much.  On the other hand, fanless
> fixtures are
> almost silent and use less electricity, which in California, is more
> of a
> concern than it used to be.
> Hope this helps.
> Roger Gordon

Personally, I don't think use of fans (forced air cooling) is bad
design.  It is one practical method of dealing with the all that
energy.  All the methods (forced air, radiation, passive convection)
have good and bad points.

A lot of factors are involved in the choice for fans, the main ones
being how much heat is being generated in how small an area (or volume)
and what the ambient temperature is -- actually how quickly the
surrounding environment can absorb that heat -- and other design
parameters such as, does the user want any glare "leaking" from the
lamp into the room.  

Since tank lights are (literally) up in the air, it is the air that
must abosrb the heat, if you want to keep the heat away from the tank. 
There are two ways to move the heat from the lamp to air in the room: 
radiate it (heat sink) or move air over the heat source.  It takes of
lot of surface to quickly radiate the heat from a well lighted plant
tank into a room.  All aluminum hoods can help, but how much surface
area is needed depends not just on the hood material but also the
ambient temps.  In warm summer rooms, you might need fins on the
aluminum hood.

RE air movement, while it is true that with enough air vents you can
cool anything, at some point you loose much of the benefit of having a
hood, which is not only to hold the lamps but to focus the light into
the tank and not otherwise into the room.  You loose much of the
benefit because with too many vents you loose much of the hood itself. 

Hoods that stand above the tank on legs allow more room air to come
into contact with the lamp heat before it reaches the tank but they
emit an unacceptable amount of glare into the room for some folks.  

Fans allow smaller vents, less surface area (not cooling fins are
necessary), allow the hood to sit directly on the tank without
"leaking" light, but create noise and use electricity.  Cheap fans
create a lot of the former and use a lot of the latter.

Scott H.

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