I Killed an Incandecant (Tapping Bulbs)

[yuandrew]

So a little earlier, I was reading and after looking up, I decided to give the Philips 75 watt bulb a quick and firm "tap" with my fingernail. Well, for some reason, the light got slightly brighter after I had tapped the bulb. Not really thinking about it much, I went back to reading. About 15 to 20 mins later, the bulb burned out with a flash and I was like "Awww!"

I recalled the same thing as well from my younger years playing with a night light bulb as well. Sometimes, tapping the bulb would cause it to burn brighter but it would then have a very short life afterwards (the night light would only last maybe an hour or so at the increased light output)

Anyone know what might be happening ?

 

[FlashSpyJ]

no but I have experienced the same thing when tapping a incandescent desk light.

 

[bfg9000]

Most likely, the long filament broke and short circuited so it was shorter. I see this on unfrosted household incans where it is often even possible to temporarily resurrect a burned-out bulb by carefully rotating it until the ends of the broken filament touch again somewhere.

Kind of like those sealed marble gravity puzzles.

 

[jrmcferren]

Most likely, the long filament broke and short circuited so it was shorter. I see this on unfrosted household incans where it is often even possible to temporarily resurrect a burned-out bulb by carefully rotating it until the ends of the broken filament touch again somewhere.

Kind of like those sealed marble gravity puzzles.

Bingo, I do this with Christmas bulbs all the time. Sometimes they will last a long time.

 

[broadgage]

The filament of a line voltage lamp is much longer and thinner than that of a low voltage bulb. Therefore to fit into the bulb, the filament is tightly coiled, and in some types the coil is again coiled.
Tapping or knocking the bulb causes the coils to collapse with adjacent turns touching, this of course reduces the total lenght of the filament and overuns it it leading to early failure.

This may be demonstrated (if you dont mind wasting a bulb) by tapping a lit bulb until it lights brighter, then before it burns out, connect to a dimmer and turn down until just glowing red. The collapsed coils of the filament will be clearly visable.

Tapping or knocking an unlit bulb can lead to failure, but this is less likely since the filament is much stronger when not heated to near its melting point.

UK type 230/240 volt lamps are even more vulnerable to this than USA 120 volt ones.

In the UK, lamps on machine tools etc are often 25 volt, worked from a transformer, this is not just for electrical safety reasons, but also to improve the lamp life since the shorter thicker filament of the 25 volt lamp is less liable to damage.

Street lighting lamps are very exposed to vibration, and used to be very low voltage lamps wired in series, again for durability.