|MLA Citation:||Bloomfield, Louis A. "Question 633"|
How Everything Works 16 Jan 2018. 16 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=633>.
As the electrons flow through the lamp's filament, they leave behind much of their energy. This energy is deposited in the tiny filament and the filament becomes extremely hot. It begins to emit much of its thermal energy as thermal radiation, part of which is visible light. So you can think of the electricity as a steady stream of tiny delivery trucks (the electrons), carrying energy to the lamp's filament, and then returning to the power company to pick up some more energy. The filament sends this energy into the room as heat and light.
When a light bulb burns out, it's because the filament has became so thin that a section of it has overheated and melted. This thinning process is caused by the slow evaporation (or actually sublimation) of tungsten atoms from the filament. A thinned filament usually fails as you turn the bulb on because that's the time of maximum power delivery to the filament and thus maximum stress. Unfortunately, it's very hard to tell in advance whether the filament will be able to tolerate the next attempt to turn it on. Probably the best predictor is the number of hours the bulb has been on. If you always replace a bulb after it has operated for 750 hours at full power, you'll probably avoid most outages.