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Re: Light bulb advice
>
> Date: Sun, 15 Oct 2000 09:15:30 -0400
> From: "Wayne Jones" <waj at mnsi_net>
> Subject: Re: Light bulb advice
>
> Wright Huntley wrote:
>
> I have been switching to compacts for my small tanks and buying electronic
> ballasts in preparation for converting my larger tanks to the far more
> efficient T-8 tubes.
snip...
>
> I reply:
>
> Do you have an idea of how close is too close for fluorescent lamps? I have
> tried to find this out for quite some time but I haven't managed to find a
> clear answer.
Really close is bad, period. The exact location is a fairly tricky
optical/thermal design problem. I will space them as far *apart* as
possible, as that gives me far more design latitude for the reflectors.
Look at the way CFs are designed, to see the absolute closest they should
ever be.
>
> Wright wrote:
>
snip... [some deathless prose!]
>
> I reply:
>
> This is one of the problem with T8s. It is hard to buy or make reflectors
> that can compete with AH Supply reflectors. You need more reflectors because
> the T8s even with the right ballast are still less intense than the PC
> lamps.
I have trouble understanding this statement. CFs are T-5 and T-8s will
*always* be a bit less efficient, AFAIK. Their absolute brightness is *way*
lower than most PCs. The reflector design can get you part way back, but
only if it is clever and terribly efficient.
If I could afford it, I would do all my larger tanks with "Brite Kits" and
have done with it. The AH reflector design is a good and clever compromise.
It keeps the plane of the CF horizontal to keep the reflector low, which
might not be the ultimate in efficiency. Arranging the tubes one above the
other does permit less restrike. It also make for ugly, tall hoods, so...
> I have the equipment to make reflectors and they work very well but I
> don't get enough light in a deep tank if I make single lamp reflectors more
> than 4" wide.
Width is no more significant than depth. The more you can afford (tolerate)
of both, the closer your reflector can approach ideal (steeper angle of
entry for more light). Tank depth has very little to do with it. It's how
much of the light enters at how steep an angle to the water. Once *in* the
water, light-piping will get it to all unshadowed areas with only a little
attenuation. [Of course, I refuse to have, or work in, a tank that is deeper
than my arm will reach. ;-)]
If scuba gear is required, then my statement, above, is obviously wrong.
> I have tried to make two lamp versions but two T8 lamps in a
> single reflector just doesn't seem to work. The ultimate in aquarium
> fixtures would be linear T5 HO lamps with one specular reflector per lamp
> made from a highly reflective material.
It would sure beat anything *I* can afford, right now. (^_^) BTW, how do you
bend the parabola?
> That is one of the reasons I am so
> interested in the merits of 800 series lamps. They don't make the T5 HO
> lamps in 900 colors. In any case though, such a fixture would not be all
> that much better than an AH Supply kit and not nearly as versatile as PCs.
WE agree on that, OK.
> Do you know offhand what the reflectivity of the 3M material?
They make various versions of "Silverlux." The expensive one (about $2/sq.
ft.) is pure silver, under thin vinyl, and is over 95%, as I recall. The
aluminum one is quite a bit cheaper, probably, but more like 85-90%, I
think. I don't have the specs handy.
>
> The other problem with T8s when compared to PCs is that they are designed to
> work at 25 degrees C. while T5 lamps are designed to work at 35 degrees C.
> Most aquarium hoods are going to be closer to 35 rather than 25 degrees C.
> On the other hand T8s are somewhat more efficient than PCs to begin with and
> last longer as well so the T8s should be cheaper to operate.
I have little sympathy for those who would design hoods with insufficient
ventilation.
Most fluorescents have the same negative response to heat. The T-5s just
*have* to put up with more. They aren't exactly "designed" to.
My 40W PC is rated at 20,000 hours. I haven't seen many T-8s rated for that
lifetime.
When I outlined where I'm headed, it should be understood that I don't have
unlimited resources, so I'm looking for practical, easy-to-home-build hoods
that won't embarrass me too much if I have friends over for a drink.
The closer I get to what *I* want, the more impressed I am with the sound
compromises that led to the AH design.
Wright
--
Wright Huntley, Fremont CA, USA, 510 494-8679 huntleyone at home dot com
If it ain't broke, don't fix it -- and, especially,
don't let politicians fix it. ... Thomas Sowell
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