Re: Reflectors and Stuff

>From: justin_frese at csufresno_edu (Justin Frese)
>Date: Tue, 31 Oct 1995 08:27:04 -0800 (PST)
>Subject: Reflectors and Stuff
>     There has been all this talk about reflectors and substitutes.  I
>have found the stuff I use to work quite well.  I have previously
>described it before.  >>>It is intended as a heat insulator<<<, and I've
>seen it at car shows intended to put in the engine compartment to
>reduce a cars cab tmperature.  >>>It looks like stiff sheets of bubble
>packing material covered with foil.<<<  It has drastically reduced the
>temperature of my hood.  It used to be very warm to the touch.
>Justin Frese    Fresno Ca, USA 

I'm also building a light fixture,  I'm trying to get around six 40 Watt bulbs 
in the hood.  I thought about using 4 and 3/8 inch wide vinyl rain gutters that 
are symmetrically beveled along what would be the top of the fixture.
It seemed that they had a near ideal shape to reflect light back down and
would fit two T12 lamps. They also come with a white inside/dark brown
outside color.  You can even use the vinyl end pieces to make it look nearly
commercial quality as opposed to home brewed.

Since vinyl is a fairly good heat insulator, I started to worry about heat
build up. I measured the temperature in a All Glass Twin Tube light fixture and
found that the steady state temperature just above the glass top inside the light
fixture to be around 120 to 130 degrees F. The bulb temperatures were much higher.
I don't think my vinyl designed fixture would  melt???, but I'm concerned about what
affect the increased temperature would have on the performance/life of the lamp.
According to Sylvania's Engineering Bulletin 0-362 a 40 Watt lamp can loose
over one third (3000 lumens to 2000 lumens) of its light output when the bulb 
temperature increases from 100 degrees F to about 160 degrees F.  I suspect that
a hood that uses materials which are good heat insulators (e.g. plastic),
one can easily exceed these temperatures.

Anyways....., what I trying to say that using a stiff sheets of bubble packing 
material covered with foil may improve the reflectivity of the fixture, but
you may loose even more light output do to decrease bulb lumen output caused
by higher operating temperatures.  Also, since the heat has to go somewhere,
an aquarium with the light fixture resting on top of the glass will transfer
the heat to the surface of the glass/water causing a significant increase in
water temperature.  Also, any plants which emerges out of the water and contact
the glass top will get burned.

I'm considering making an all aluminum box fixture for better heat dissipation.
I definitely want to separate the ballasted from the hood.
Definitely interested in the white or polished metal reflector thread.  
Anybody have ideas one when a cooling fan pays off for a hood?

Ron Wozniak  Allentown PA, USA