> Looking for some insight as to the purpose of a resistor in a desk
> lamp... specifically, an illuminated magnifier, 120V AC lamp that 
> has a
> circular Flourescent tube. The lamp was not working, and I tracked 
> it
> down to a failed-open resistor, 0.1 Ohm 5% 1W in series with the 
> live AC
> current.

*IF* it is what you say it is then it has to be intended to act as a 
fuse - and as a very gross one at that. It serves no useful purpose 
otherwise due to its low value.

BUT I = sqrt(Power/R) = sqrt(1/0.1) ~= 3 Amp at rated wattage.
That would only fail under heavy short circuit or a load of 1 kW plus.

POSSIBLY it is a PTC which is meant to have a higher value when hot. 
This also seems unlikely.  The fact that it has failed suggests either 
that you have been trying to run heaters from your lamp :-) or that it 
is not what it appears to be (or that it was faulty).



        Russell


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