Light bulb longevity I have a summer home in North Carolina where there are more people in the summer than in the winter.  Light bulbs seem to last longer in the winter when there is less demand on the system.  I suspect the line voltage drops with the higher use.  Would this affect the life of the bulb?
 A: You may have noticed that filament light bulbs often fail when the bulb is switched on.
This happens because when a bulb is switched on for a short period of time the current through the bulb exceeds its normal operating current.
This behaviour is shown for two different wattage filament light bulbs in the graphs below.  

The reason for the larger current on switching on is that when cold the resistance of the filament is much less that when it is at working temperature.
So there is a power surge when the bulb is first switched on which could lead to excessive heating and the filament breaking.  
When hot there is some evaporation of the filament and this can lead to a narrowing of the filament in a small region.
This in turn leads to a larger heating effect in that region thus increasing the local temperature and hence the rate of evaporation in that region.
Thus this avalanche type process results with the probability of the filament breaking in that region increasing.
Putting gas inside the bulb reduces the rate of evaporation and hence increases the lifetime of the bulb.  
The more often a filament bulb is switched on (and off) the more chance there is of a failure and it is probable that during the winter in North Carolina light bulbs stays on for long periods of time and are switched off less often than in the summer.
A: The bulb life highly depends on the voltage. The lifetime is limited due to tungsten evaporating from the filament. This process is more intense at a higher voltage, especially because the heat power is proportional to the square of the voltage.
Having said this, the voltage usually drops with higher use, which is in summer. So your observation is reverse to what would be normally expected. Is it possible that the bulbs last longer in winter, because you are not there in winter as often and don't use them as much as in summer?
