Incandescent Bulb Blackening

Animated graphic of tungsten filament evaporating and depositing on the glass bulb. Tungsten filament breaks when enough atoms evaporate off of it. Bulb blackening was the number one problem that early light inventors had to deal with before Edison and Swan (1805-1879). Edison and Swan were finally able to create a good vacuum which controlled blackening. Still, blackening happens today, usually at the top of the bulb first. Today the filament breaks before the bulb blackens.

Category:

Science & Technology

Tags:

• light bulbs
• life
• hours
• blacken
• deposit
• evaporation
• ductile tungsten
• filament
• atoms
• burn off
• glass bulb
• evacuated
• argon
• bulb life
• engineering

[EdisonExploratorium]

This is a super simplified model to show the act of blackening, another model could be done to show why it breaks at certain points over others.

[CampKohler]

Wouldn't the tungsten evaporate evenly over the entire filament (except perhaps wherever the support wires touch and cool the filament)? Then, instead of a clean break in an almost-new-appearing fillament as shown, the filament would gradually thin, until one day it becomes so fragile that it breaks from the thermal shock of starting up.

Does the distance from the filament to the glass (say in a bigger envelope) make a difference in the blackening rate or whether it will at all?