Steph's Friend

Saturday, March 26, 2005

Tungsten Vapour

Have you ever noticed in older bulbs they have a black deposit on the inside of it afrer long use? Some people may think that it's dust while others think that it's just their eyes playing tricks on them. For me...I didn't have a single clue as to what it was until I found the answer.

It's actually tungsten!! In a light bulb, the gas is an inert one such as argon or krypton. It's not oxygen as it will react with tungsten to give tungsten oxide. This might reduce the efficiency of the light bulb. As the filament gets hot (this is where your light comes from), some of the tungsten evaporates and condenses on the cooler glass surface. Hence the black deposit. This only happens when the light bulb is really old.

Neat huh? So next time you see a dark light bulb, you know that it's time to change your bulb.

(Found the answer from a book from a local library)


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