> And another thing - filament bulbs are designed to work best in a
> certain orientation - true ? True at one time ?

I believe the problem comes if you change the orientation after they have been
operating for some time. The filament can get a sag in it from being heated for
long periods of time, and if you move the bulb the filament can shake and touch
other points, resulting in a shorter electrical path which results in higher
current which results in brighter but shorter life.... which is why you can get
ruggedised bulbs for use in items like trouble lamps. These are reputed to have
stronger filaments and more filament supports so they can withstand movement
while powered on.

Another possible failure at switch on is reputed to be the filament moving due
to magnetic effects resulting in the filament touching where it shouldn't. This
is often seen by the bulb giving a bright flash at switch on.

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