Extending Bulb Life

I've added series resistors to household bulbs to stop the damn things blowing with annoying regularity. Two household 60W spot bulbs have a 47R 10W resistor in series, two have 2 x 47R 10W resistors in series. Two others have no resistor (ie normal operation)

Here are some ongoing results -

60W filament bulb
House voltage 240VAC
47R 10W resistor has 11.4VAC across it
Bulb now has 229VAC @ 0.27A across it (95% of house voltage)
Still a good white colour
Resistor reaches top temperature of 63 degrees C in 15 minutes
Neither bulb has blown after eighteen months (as of June 2002)

For two resistors -

Voltage across bulb drops to 213V (89% of house voltage)
Colour very slightly yellow but still bright
Neither bulb has blown after eighteen months (as of June 2002)

For no resistor -

One has blown already and I expect either to blow whenever I flick the switch (update - both of these bulbs have now been fitted with a resistor)

This is a chart from GE showing how bulb life is affected by running voltage. I expect the bulbs with series resistors to last a very long time. Each resistor costs around $1, so it's a very cheap way prolonging the life (which presently doesn't seem to be long at all) of a $3 bulb perhaps 10 times or more. This would be more than the chart indicates, but the resistor should take some of the stress out of turn-on as well as make the filament run very slightly cooler

Bulb Life Chart