>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 28 June 2006 16:29
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Predicting keep alive voltages for incandescent lamps
>
>
>> I replaced one of of the (series string) bulbs with a (carefully
>> insulated) 1N4007 to knock the voltage down to 70% of line and get 
>> several years lifetime 24/7.
>>
>
>
>Which reminds me... Some projectors use 70V lamps. I assume 
>they get the 70V by half wave rectifying the 120VAC line. But 
>why not just use a 120V lamp? I'm guessing that it MAY have 
>something to do with being able to have a shorter filament 
>making the light more of a point source and easier to focus. 
>Is the guess correct?

That sounds reasonable. The only other explanation I can muster is that lower voltage lamp filaments are physicaly tougher as they are shorter and thicker, which is why standard house lamps don't last too long in inspection lights.

Regards

Mike

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