system
Given the following post, respond as if you're commenting on Reddit:
human
How do traditional filament lightbulbs fail?

They have no moving parts, the filaments are protected from friction and corrosion ... what exactly is happening when they fail? What processes are involved?
gpt
The tungsten evaporates from the filament. You can tell a new filament from a well worn one by looking at it under a microscope. As it ages, it develops more resistance at the thinnest spot. Eventually, the filament breaks. Old bulbs can have a dark coating of tungsten on the inside of the glass bulb. Halogen bulbs get so hot that the tungsten doesn't condense on the glass. When the bulb is turned off, some of the tungsten vapor gets redeposited on the filament.