Re: [ATM]: What do they offer:

[Stan Truitt <s.truitt@verizon.net>]

Aloha Dave,

<Will someone offer me an explanation for what the "advantages" of LEDs are,
<compared to VERY BRIGHT incandescent filament lamps? I just have never been
<able to figure this out. I'm sure it's not a fad;' it's just probably
<because I am stupid about these things.

While being a fan of incandescent Tungsten, and to a lesser extent 
Zirconium arc lamps, I would like to share an experience relating to 
LED sources.  In an ellipsoid being tested with the knife at it's 
long focus and the source at the focus closer to the mirror, 
convection currents from the heat dissipated within the light path 
seriously disturbed data repeatability.  Efforts in ducting away the 
heated air, and water cooling the lamp surround, improved the setup; 
but not without blocking an unacceptably large area at the mirror's 
center.  Switching to the vastly more efficient LED source while 
retaining a bit of the water cooling resulted in excellent 
repeatability of the data, even with the water flow turned off.

Perhaps you are not "stupid about these things", rather than highly 
enthusiastic about those things that worked for you.  Patient 
forbearance of others' curious investigation of alternate avenues 
seems, to me, a good way to go!  Pontificating is, at least for me, 
not.

Tungsten ribbon lamps are a practical necessity in the double bounce 
from uncoated Cass secondaries in Hindle sphere setups.  Not to 
mention providing a fine place atop the lamp housing to set my 
pyroceram coffee cup!  Coherence effects in porting my HeNe beam to 
this setup make the filament approach all the more desirable.

I enjoy many of your messages to the ATM list.  Some, for me, have 
been valuable.  Your kindness and generosity garner my appreciation 
and sometimes admiration.


Sincerely,

Stan Truitt
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