🚀 go-pugleaf

Phil Hobbs wrote:
> 
> On 10/12/2012 01:38 PM, Michael A. Terrell wrote:
> >
> > Phil Hobbs wrote:
> >>
> >> On 10/11/2012 07:18 PM, Dave Plowman (News) wrote:
> >>> In article<ju2e78dvhsud46mljvoujn8kn69bqikpjr@4ax.com>,
> >>>      Jeff Liebermann<jeffl@cruzio.com>   wrote:
> >>>> The lobby and foyer lights were mounted on the ceiling, pointing down.
> >>>> One would think that there would be plenty of hot air accumulating
> >>>> near the ceiling, but that wasn't the case.  That's where the fan
> >>>> ducts were located which helped to cool the lights.  Few of those
> >>>> lights ever burned out.
> >>>
> >>>> The marquee lamps were mounted on a vertical structure, with the lamps
> >>>> pointed horizontally.
> >>>
> >>> Vertical mounting for a GLS lamp seems to give a better life than other
> >>> orientations. A rough service type may have had a better life in this
> >>> application.
> >>>
> >>
> >> The filament temperature goes up more slowly than the ambient, since
> >> it's radiatively cooled, but a rise of, say, 50 degrees would probably
> >> have a significant effect on bulb life.
> >
> >
> >     The projector bulbs in the old RCA TP66 film chain were mounted in a
> > vertical line.  If you used the bottom lamp, and let it switch the to
> > spare on top, they had a short life of a little over 20 hours.  If you
> > ran the top lamp, with the spare at the bottom, the life was over five
> > times longer.  The projector used a motorized track, with a relay in
> > series with the filament. When the filament opened, the relay dropped
> > out and turned on the motor.   In either position, it would run to look
> > for the other bulb when the one in use failed.  I would pull the bad
> > lamp and move the good lamp to the top at the next film change, then put
> > the new lamp in the bottom socket.  I averaged over 130 hours per lamp,
> > that way.
> 
> That's interesting--just storing the bulb at higher temperature reduced
> its life that badly, even if it wasn't energized?  The only mechanism I
> can think of for that is that they leaked and let oxygen in.  Otherwise
> glass and metal should be unaffected by ~100 C temperatures.  But then
> they should leak even worse when energized.  Another mystery, Scoob.
> 
>   Hot tungsten doesn't have a very high emissivity in the IR, so
> probably the filament temperature is more sensitive to ambient
> temperature than one would expect from the T**4 dependence from Stefan's
> law for black bodies.  Raising the temperature by 1 degree at 3000 K
> makes the radiation go up by 1000 times more than at 300 K, so the
> filament regulates its own temperature quite closely if it's really a
> black body.


   The glass on these projection lamps was usually distorted, by the
time they failed.