🚀 go-pugleaf

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.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net