Light Bulb

[Tarantism]

i heard once that the first ever lightbulb that was made is still burning today. what im curious about it that if the lightbulb is still burning then do ours just go out becuase lightbulb companys want profit, or is the first story a myth? :confused:

[Tormod]

Definitely a myth. Light bulbs work by forcing electrons through carbon filament, and this filament eventually wears out and breaks apart.

[Tarantism]

Definitely a myth. Light bulbs work by forcing electrons through carbon filament, and this filament eventually wears out and breaks apart.

oh i see, siily me!

[Boerseun]

Definitely a myth. Light bulbs work by forcing electrons through carbon filament, and this filament eventually wears out and breaks apart.

I thought commercial bulbs used a Wolfram filament in an inert gas?

[infamous]

I thought commercial bulbs used a Wolfram filament in an inert gas?

Quite right Boerseun; actually Wolfram by it's other name..........Tungsten ..........because of it's very high melting point of 3410 C or 6170 F

[Tormod]

I thought commercial bulbs used a Wolfram filament in an inert gas?

 

Ah, well, my point was that the first light bulb that worked (ie, Edison's) used a carbon filament. :confused:

[Boerseun]

Quite right Boerseun; actually Wolfram by it's other name..........Tungsten ..........because of it's very high melting point of 3410 C or 6170 F

Sorry 'bout that - had my multilingual periodic tables all mixed up! Good thing I'm not calling Carbon Koolstof - that'll be just plain rude...:confused:

[CraigD]

i heard once that the first ever lightbulb that was made is still burning today. what im curious about it that if the lightbulb is still burning then do ours just go out becuase lightbulb companys want profit, or is the first story a myth? :confused:

This story contains an element of truth.

 

To understand how, we need to look in detail at how an ordinary incandescent light bulb works, and what causes it to eventually fail.

 

Modern (post 1920 or so) light bulbs produce light by passing electricity though a tungsten filament surrounded by an inert gas, such as nitrogen, argon, or krypton (not, as is commonly believed, a vacuum). The exchange of electrons between tungsten atoms that constitutes the electric current causes those electrons to emit light, mostly (98%) in the infrared, but also in the visible spectrum.

 

Occasionally, the electrons of an atom are so excited that the atom breaks the bonds with its neighbors, and one or more atoms evaporate into the surrounding gas. Eventually, the filament becomes so thin it breaks - the light bulb has then failed.

 

If the filament evaporated evenly, it would be easy to make a nearly “immortal” lightbulb – just make the filament thick enough that it takes a century or more to evaporate away. Unfortunately, the evaporation is not even – as a bit of the filament evaporates, that section of the filament becomes slightly thinner. The amount of current passing though each atom becomes slightly greater, causing the rate of evaporation to increase, eventually leading to a runaway feedback loop that causes the filament to break at that point, while the rest of it is near its original thickness.

 

Also, the filament is under strain from vibration – not only vibrations from the outside world, but from constant expansion and contraction due to heating from the 60 times-a-second changes in current that is modern AC current (if you observe a lightbulb closely, you can sometimes see and hear this vibration). This can cause the filament to break sooner than it would if not for the shaking. The thermal stress on the bulb is greatest when its switched on and off, which is why bulbs often seem to burn out “when they’re off”, or immediately upon being switched off.

 

There are ways to make an ordinary light bulb last much longer – potentially forever – among them: use DC current; and lower the supplied voltage, which lowers the current, and also, the emitted light. Several light bulbs emitting less light can be combined to emit the same light, so such a scheme can make for very long-life light bulbs. It’s impractical, however, to wire homes and businesses with special low-voltage lines and low-intensity fixtures, or to build circuitry into each bulb to condition the electricity – it’s cheaper just to keep buying new bulbs, or use halogen or florescent bulbs.

 

Early (19th century) light bulb research prototypes, however, were usually powered by low-voltage DC power supplies (often batteries), so claims that these labs kept low-output prototype bulbs burning continuously for many years are reasonable. Some museums have examples of these prototypes that can still function. None of these museum pieces, to my knowledge, are left on for extended periods any more.

 

There is at least one documented case of a light bulb that has been on continuously (except for a couple of moves and the occasional power outage) since 1901 – see http://www.snopes.com/science/lightbulb.asp. Given its age, it’s likely to have “squirted” cellulose, or perhaps even bamboo, filament, rather than the more modern metal plated carbon or tungsten.

[CraigD]

Ah, well, my point was that the first light bulb that worked (ie, Edison's) used a carbon filament. :confused:

Now that’s a myth! I though that “Edison invented everything” myths were unique to the US – apparently, they’re not B)

 

The first successful incandescent light bulbs (ca 1820) used platinum strips or wires, and were too expensive to be practical. Since good electric arc lamps had been around since about 1810, the incandescent bulb remained a technological oddity for another generation.

 

The first practical bulb (ca 1855) used carbonized bamboo. Edison’s prototype (ca 1880) did use carbon, but his first commercial version used bamboo.

 

Source: http:// http://en.wikipedia.org/wiki/Incandescent_light_bulb#History_of_the_light_bulb

[cwes99_03]

I think he meant 1810 not 1910.

[CraigD]

I think he meant 1810 not 1910.

Indeed. I've corrected it. Thanks for the catch.