The life of incadessent light bulbs is a very well understood function. It is the applied voltage to the fifth power. At any given voltage level you can have a very bright light which burns out quickly,or a dim light that lasts a long time.
Did you ever notice the behavior of the red lights at railroad crossings. They run those standard 115 volt bulbs at 90 volts, and, even with many ON/OFF cycles, can expect a life of 100 years. Bulbs made for EXIT signs are also made to last a long time. The landing light bulb in a Piper Cherokee plane is good for less than 100 hours, and the damn things cost about $40 :-(