I have been reading the bulb-life discussion,
specifically regarding the doubling of the
bulbs life expectancy from dropping the AC voltage
a few percent.

I just want to state that you can get many times
this effect from adding a series resistor, which
drops the voltage as desired, BUT ALSO reduces the
start current of the cold filament. So if just
dropping the voltage 5% can give double the bulb
life, doing this with a series resistor can give
10x or more bulb life.

I measured a 240vac 60w bulb, at 60 ohms cold.
If you turn on the switch at the ac peak, this will
give 340v into a 60 ohm filament!

That is worst case power of 1927w,
Almost 2kW!!! No wonder they blow every ten weeks
or less, and I have "light bulbs" on most of my
shopping lists.

If you drop just 5% of running voltage with a
resistor, with a 60w bulb it needs about 50 ohms
series resistor. The bulb gets 5% less volts when
running and is almost as bright.

BUT! Now at cold start the worst case power in
the filament is almost a quarter of what it was,
and the number one cause of bulb death is virtually
eliminated. It's quite possible to get 10 years
or more from an incandescent bulb, maybe 20 or 30
times the "normal" life span.

I learned this from an old electrician when I was
an apprentice. He did this 5% trick on some of
the bulbs in very high places. And some bulbs
were so old they were almost black. :o)

What irks me is that the bulb manufacturers could
very easily add a 5% wire resistor into their filament
designs, and make bulbs that last almost forever.

They just rip us off in a cold calculated fashion
with products designed to last a few weeks!!
-Roman

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