"Jim Yanik" wrote in message
4...
"Ian Field" wrote in
:


"David Lesher" wrote in message
...
"Ian Field" writes:



If you run a lamp on DC the almost molten tungsten gradually migrates
to one
end of the filament leaving weak spots at the other end where it
becomes thinner - this shortens lamp life compared to running on AC.


Flip the lamp in the socket monthly, maybe?

The migration is extremely lumpy so you still get weakened spots on
the relatively thicker sections of the filament, and I vagely remember
the book I read years ago explaining why reversing the DC doesn't help
as much as you'd expect - unfortunately I can't remember what that
explanation was.




if the lamp has a transformer,why is the bulb running on DC?
transformers output AC.
you would have to add an extra component(diode) at more cost,and for
lesser
performance.

Or is the "transformer" actually a AC-DC switching converter?


All the electronic 'transformers' I've looked inside had a circuit
remarkably similar to a CFL - except no ballast coil and the primary of a
toroidal transformer is half bridge style between the O/P & divider
capacitors.

AFAICR I've never seen one with a secondary side rectifier.

It just happened that someone suggested DC operation and I'm one of those
pointing out that it wouldn't provide optimum lamp life.