Electronic – What are the effects of AC vs DC for an Incandescent bulb life


What are the effects of AC versus DC on incandescent bulb life? Provided the same amount of power is being delivered to the bulb.

Best Answer

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.


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.