"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.