Final answer:
Electron arcing from the filament to the glass envelope in a light bulb leads to bulb blackening due to tungsten atoms depositing on the glass, which diminishes light output and shortens bulb life.
Step-by-step explanation:
When electrons begin to arc from the filament to vaporized tungsten on the glass envelope in an incandescent light bulb, it can lead to a phenomenon known as 'bulb blackening'. This occurs because the high temperatures cause tungsten atoms to evaporate off the filament and, if these atoms come in contact with the cooler glass, they settle on it, leading to a thin tungsten coating that darkens the bulb. This reduces the light output and can shorten the bulb's lifespan. Incandescent bulbs contain a tungsten filament housed in a partially evacuated glass envelope or one filled with an inert gas to minimize this effect. Furthermore, the inside surface of the glass envelope may be coated with a reflective material to reflect infrared radiation back to the filament, thus increasing its temperature with the same amount of electrical energy and improving energy efficiency.