In article , Chris Lewis wrote:
Random responses:

These are brand-new (less than a year old) ceiling pot fixtures. A
"standard" HD brand of some sort. Cheapies, but reasonably well built.
Rated at 100W I believe.

BR30s are medium size incandescent flood lights, 60W apiece - the fixtures
are designed specifically for this size. The halogen equivalent is "PAR30"
IIRC.

So heat is unlikely to be a problem. We haven't even installed the fixture
bezels yet.

Vibration is certainly a possibility, but we're aware of it (I wrote the
FAQ on that! ;-), and some of the lights that are dying aren't anywhere
near floor space likely to have much vibration. CFs on the same area (in
previous ceiling mounted J-boxes, same switches) also _seemed_ to have a
relatively shortened lifespan.

Fixtures as described above are notoriously hard on compact
fluorescents. (Less of a problem for most CFLs 13 watts or less, as well
as Philips SLS excluding versions 25 watts or more or dimmable). So I
suspect rough heat situation for early failure of compact fluorescents,
and fair-good chance of a different reason for early failure of
incandescents - most likely bad brand or bad lot of bulbs, after that
significantly high line voltage or vibration.

There is no aluminum on (or upstream) of this circuit. The only aluminum
is a subpanel feed to the garage.

No, we're not having dimming/brightening problems. Many other bulbs in
the house have more than adequate lifetimes (ie: 10 year+ on some reasonably
well used flood lights). So it's not an overall voltage problem.

As we've not had a lot of luck with CFs on this circuit already,
I'm hesitant about going for them until I understand what's happening.

[Our kitchen ceiling lights also have similar problems, despite being
on a dimmer.]

If you are using the dimmer as a soft-starting means, please be aware
that soft-starting usually increases incandescent lifetime only a little.
Some incandescents even suffer vibration problems from the spiky current
waveforms when dimmed by usual dimmers, to an extent such that dimming
only slightly extends their lives. (Most incandescents have major life
extension from dimming, although with energy efficiency decreasing badly
enough for cost of achieving a given level of lighting to actually
increase.)
Most halogens have an aging mechanism slowed only a little by dimming
and a few halogens have contaminants that dominate and wreak havoc when
major dimming is done.

I should check the voltages on this circuit just in case. A pair
of new switches is probably a good idea too.

- Don Klipstein )