From: utzoo!decvax!ucbvax!CAD:teklabs!keithe
Newsgroups: net.invest
Title: bulb savers
Article-I.D.: teklabs.1575
Posted: Wed Dec  1 08:08:30 1982
Received: Sun Dec  5 15:49:08 1982

I remember the old, old 16mm movie projectors having a four-position
(rotary) power switch - two offs and two ons. The reason for two ons is
that the sound-track exciter lamp was run on dc (ac would put hum in
the sound), and the two positions ran the current through the bulb in
opposite directions. Thus, over enough on/off cycles, the bulb would
have the exciter current run through it in each direction equally.
When I asked (someone) "why" I remember being told that it was to
increase the bulb life; for some reason running the current only one
way thru the bulb apparently reduced the filament life. Now, this may
have been on a differently-constructed bulb than a standard light bulb,
but it still makes me wonder about putting a rectifier in series with
one.

keith ericson