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incandescent light question

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Gilles.Thesee(at)ac-greno
Guest

Posted: Mon Apr 06, 2009 1:14 am Post subject: incandescent light question

Hi Bob and all,



The topic has already been adressed, but I was not able to retrieve the 

messages or Bob's recommendations on preheating.



The question recently arose on a French pilot list : when and why is a 

landing light filament most fragile ?

- When hot ?

- When cold ?

- When heating up ?

- When cooling down ?

-Why ?



Etc...



Thanks in advance for any input,

Best regards,

-- 

Gilles

http://contrails.free.fr

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Mon Apr 06, 2009 5:22 am Post subject: Re: incandescent light question

Gilles,



The common wisdom is that most lamp failures occur on start due to

three factors:

cold filament stiffness

heat shock/expansion

and 3) flexion of the stiff filament due induction of the magnetic field

in the helical filament



Ira

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_________________
Ira N224XS

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Apr 06, 2009 5:42 am Post subject: incandescent light question

At 04:12 AM 4/6/2009, you wrote:

 	  Quote: 	
		  

<Gilles.Thesee(at)ac-grenoble.fr>



Hi Bob and all,



The topic has already been adressed, but I was not able to retrieve 

the messages or Bob's recommendations on preheating.



The question recently arose on a French pilot list : when and why is 

a landing light filament most fragile ?

- When hot ?

- When cold ?


	


   Tungsten passed from a brittle to ductile state

   as it rises in temperature. The legacy automotive

   lamp filaments were most vulnerable to vibration

   stresses while cold.



 	  Quote: 	
		  - When heating up ?


	


   Thermal stresses are highest during heat-up

   transition.



 	  Quote: 	
		  - When cooling down ?

-Why ?


	


   Modern halogen lamps are MUCH more robust than

   their ancestors. So much so that concerns about

   inrush limiting are almost insignificant in

   terms of adding to the service life of a lamp.



   Even when the halogen lamps are used in a wig-wag

   system, they do not cool enough between flashes

   to suffer a deleterious inrush current with each

   flash. See:



http://www.aeroelectric.com/Pictures/Curves/Exemplar_Incandescent_Lamp_Inrush.gif



http://www.aeroelectric.com/Pictures/Curves/Wig_Wag_Currents.jpg



    For new design, I'm certain that the builder

    will experience very good service life using

    modern automotive halogen lamps operating without

    benefit of inrush limiting.

        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

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Gilles.Thesee(at)ac-greno
Guest

Posted: Mon Apr 06, 2009 11:15 am Post subject: incandescent light question

Robert L. Nuckolls, III a écrit :

 	  Quote: 	
		  

   Tungsten passed from a brittle to ductile state

   as it rises in temperature. The legacy automotive

   lamp filaments were most vulnerable to vibration

   stresses while cold. 


	


Bob, Ira and all,



Thanks for your response.



Best regards,

-- 

Gilles

http://contrails.free.fr

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