Re: [AGA Member] Fluorescent Reflectors efficiency

["S. Hieber" <shieber@yahoo.com>]

What makes a good reflector are thre things:

How little light it absorbs--how much light it reflects
without further diffusing it;

How durable it is--how fast it wil corrode and lose it's
specular properties;


How well it reflects light to where you want it.


That third one varies on circumstances. If you want the
light to spread as little as possible, then a parabolic
shape is best. Consider a point source of light. If you
properly place a point source in the center of a prabolic
reflector, all the rays coming from the light source and
going to the reflector will be reflected straight forward.
Smooth curves would be ideal, other things being equal.

With a line source, like fluorescent tube, then the choice
would be a long straight relfector whose sides are
parabolic curves. However, fluorescent light is so diffuse
comeing from the bulb, you'll never get a straightforward
(pardon the pun) reflection. Double tube bulbs (PCs) make
things a tad worse since neither tube will be right on
center. And making things a bit harder is the fact that
fluorescents are really a line source either; the light is
emitted from all over the tube. A fluorescent is a tube
source and not really a line source of light; the light is
spread out right at the bulb.

If you want light to spread more than a parabolic provides,
then something less than praboic is preferred and vice
versa if you want it be narrower.

The best material around for the first and second
properties (reflectivity and durability), I believe, is
Miro, a coated polished aluminum. The coating that makes
the aluminum resist corrosion absorbs very little light and
that's the key.

For an example of very good reflector made of Miro,
consider the AHS reflectors. They are angled because, I
suspect, it's tons easier to get them into shape by bending
them on a brake than to try to get smooth curves with a
more complex machine that rolled or stamped the shape.

The diff between the psuedo-parabolic shape of an AHS
reflectors and one that was true parabolic is probably
negligible -- bigger diffs exst between brands of bulbs,
how well the bulb and ballast are matched, how long you use
the bulb, and maybe even room temps.

Also, being angled, they are easier to adjust to suit your
particular purposes. You can relatively easily widen or
narrow the angles, and thereby widen or narrow the spread
of the refelcted light, without damaging the reflector. It
would not be as easy, I think, with smooth curves -- some
portion of the curve would always want to "give" first and
you'd end up with a dent or a buckle instead of a smooth
curve.

The amount of UV coming from a good fluorescent bulb isn't
much. Enough to darken your Photo-gray eyeglass lenses but
not to darken them al the way. If you have a glass top on
your tank between the bulbs and the water, then there isn't
much UV getting through to the water. Water also abosrbs
true UV pretty well. So there isn't much UV getting down
into the water. 


Btw, the worst reflectors in terms of shape are ones that
are flat or square in cross section. So individual
refelctors for each bulb do a better job than refelctors
that wrap several bubls. Theorhetically, straight tube T5
bulbs can beat out bent tube/u-tube PCs with the right
reflectors.

So the short answer is, no angled isn't better, other
things being equal. But given real workd conditions, you
won't find better refelctors than AHS's, imo.

Hope that's some help. It's a complicated subject and I
only know this [ ] much. ;-)
sh

--- Amit Brucker <amitb@gtek.co.il> wrote:
> Thank you all for your help on deep tanks.
> I was reading that reflectors (depending on their
> material, shape and quality) can increase the light
> source in about 40-60%. I am aware of two kinds of
> reflectors:
> 1. The rounded ones 
> 2.  Angled ones - which are better than the first kind
> because of their shape which increases the light even
> more.
> 
> Questions:
> 1. Can anyone approve this info ?
> 2. Is it 'Fair' to include the reflectors when
> calculating the W/G into account ?
> 3. There are some special fluorescent that are covered
> with a special coating which acts as a UV filter that is
> helping to prevent algae - Is that so?
> 
> Thanks
> 
> Amit Brucker
> www.plantica.com
> 
> 
> 
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