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Re: AC vs DC lamps

In a message dated 97-01-27 12:37:59 EST, you write:

<< Hello lighting mavens:
      On the subject of lamp life versus ac ripple, it is my 
 understanding that tungsten lamps last longer with ac than dc.  
 Perhaps the positive end of a dc fed lamp emits tungsten ions easier, 
 thereby preferentially weakening the filiment at that point.  Whether 
 this materially matters to a tungsten-halogen lamp with its tungsten 
 replacement cycle, I cannot say.  In any case, the level of ac ripple 
 at the alternator, given reasonable wiring and battery health, is 
 unlikely to have any effect at all.
I always used battery feed, found Halogen life extended considerably, all
else being equal, some practical engineering.  Interesting to note that KC
quoted the 9004 "standard" bulb at 300hours, the H1 at 150 hours.  I find
both those numbers on the low side from "experience," though I wanted some
confirmation from some other sources before accepting that number as the
rule, esp. considering they are the Highest claimed lumens per watt ratio
(XSM vs Halogen) @ 3.85

There has been some debate on the "capacitor" effects of battery vs alt
voltage.  I got so many conflicting data refs on this (here on the list as
well), that I just went with my experience, battery.