Re[2]: AC vs DC lamps

[KSMITH1@mailgw.sanders.lockheed.com]

I think that if lamp life is truly better hooked to the battery than 
to the alternator, it is the result of lamp life being related to some 
high power (I recall 4) of the voltage, so a small decreases in 
voltage leads to a significant increase in life.  Just what the 
difference is depends on the impedance of the alternator-battery 
connection.  An alternator generating 100A peak currents into a 0.05 
ohm circuit could generate 5 volts of peak ripple on top of the 
battery voltage.  Its not the ac component of the ripple but the 13.6V 
for a charging battery plus 5 volts of interconnecting wire drop that 
gets you!

Note that for the same life, a tungsten-halogen lamp will generate 
more lumens per watt than basic tungsten because the color temperature 
is higher.  The spectral output peaks closer to the visible.  (Both 
are in the infrared.)  That is why the HID is more efficient; its 
color temperature is close to that of the sun and the eye's 
photometric response.


______________________________ Reply Separator _________________________________
Subject: Re: AC vs DC lamps
Author:  QSHIPQ@aol.com at INTERNET
Date:    1/27/97 1:15 PM


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.

Scott