Russell,

On Mon, 28 Nov 2005 22:46:16 +1300, Russell McMahon wrote:

>...
> I am currently PWMing halogen bulbs at 1 kHz plus at present for a 
> non-automotive application but don't have any lifetime data yet.

Dimming halogen lights it generally a Bad Thing, because they need the heat of their full-on state to cause 
the tungsten that has evaporated to be re-deposited on the filament (the so-called Halogen cycle).  If you 
lower the temperature, the tungsten deposits on the inside of the "glass" (actually some form of manufactured 
quartz) and is lost from the filament.  Result is a dimming of output because of occlusion, and premature 
failure of the filament.  Sometimes *very* premature!

There's a trend to fit extra-low-voltage halogen lights in houses here, and because they create a very intense 
light some people want to dim them.  They then find out the drawbacks as above!

Of course in the OP's case, we're not talking about halogen lights anyway...

Cheers,



Howard Winter
St.Albans, England


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