What are the effects of AC vs DC for an Incandescent bulb life?
From what I understand, with low voltage it isn't very much of a problem (as the filament is thicker)

With 120, 240V bulbs, with very thin filament, DC leads to shorter life due to some sort of... filament mobility...

Here's a quote from Osram's site. Mind you this is specific to halogen bulbs, which do run the filament in more torturous conditions. I'm not certain if it matters as much on standard incandescents? Someone can fill us in.

Come to think of it, it likely to only affect halogens, due to their method of operation. They boil filament off during normal operation, and it resettles on itself, due to reaction with the halogen gas. Presumably it settles to one side when running on DC supply, leading to the much shorter life. 


  Question
  
  Can halogen lamps also be operated with direct current? Answer
  
  With low-wattage, high-voltage (230, 240 V) halogen lamps, a drastic
  reduction in the service life must be expected with DC operation. For
  example, with the 60 W lamp only approximately 15 % of the nominal
  value is achieved. The reason for this is the increasing material
  movements in the tungsten wire of the filament. Higher-wattage lamps
  with their larger wire diameter are less critical in DC operation.
  This is similar for the low-voltage lamps (12 V), as here the critical
  limit is low due to the generally larger wire diameter of these lamps,
  i.e. below 20 W.