Russell wrote regarding 'Re: [EE] means of dimming auto tail light?' on Mon, Nov 28 at 04:10:
[...]
> Here's a simple but useful primer on driving incandescent bulbs
> 
>        http://www.allegromicro.com/techpub2/an/an295012.pdf
> 
> Adding either a "warming resistor" or a series limiting resistor will 
> increase lamp lifetime and give the driver an easier job. Both methods 
> have good and bad points.
[...]

The warming resistor I think might be a bad idea, since the brake
light circuit is constant-power (so the brake lights work even if the
ignition circuit has some problem), and I'm not sure if it'd be worth
the complexity to add in an ignition-powered warming circuit (which
would require another wire running the length of the car).  If I power
the PIC and everything from the brake circuit, though, then there's
really no warming time and it's useless. :)  A series resistor might
be an alright idea, though it seems pretty inexpensive to come up with
a FET that'll handle the inrush by itself (as you said in a trimmed
part).  I hadn't thought about the low initial resistance, though, and
am glad that several people pointed it out.  Hooray for smart people!
:)

--Danny
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