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Re: [Shop-talk] looking for small light bulbs

To: Steven Trovato <>
Subject: Re: [Shop-talk] looking for small light bulbs
From: Pat Horne <>
Date: Mon, 25 Feb 2008 17:02:00 -0600
Agreed.  If dimming isn't necessary I'd try a white LED and add a series 
resistor to get the desired brightness.


Thusly spake Steven Trovato:
> Yes, yes.  I was really thinking you would just compare the resistance 
> of the known bulb with the resistance of the candidate bulb.  The V=IR 
> part was a not very well thought out afterthought.  Sorry.  In any 
> event, I think we're overanalyzing this whole thing.  There are little 
> bulbs out there of appropriate voltage.  Try some and find one that 
> looks like it's the right brightness.  Done.
> -Steve
> At 04:56 PM 2/25/2008, Pat Horne wrote:
>> Steven,
>> Cold resistance of a bulb is much lower than hot resistance. That's 
>> why most bulbs burn out when you turn them on.
>> While it may not have an exact correlation, I just measured the cold 
>> resistance of a 130V 75W bulb and it measured 21 ohms. That would be 
>> 804 Watts cold filament dissipation. Using Ohms law, the resistance 
>> of a 130V 75W lamp will be 225 ohms hot, so you might be able to 
>> measure the resistance of another lamp and multiply the resistance by 
>> 10 to get hot resistance, but my measurements is just a sample of 
>> one. YMMV.
>> Peace,
>> Pat

Pat Horne, Owner, Horne Systems 
(512) 797-7501 Voice            5026 FM 2001  Lockhart, TX 78644-4443
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