Edison and his light bulbs
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Thomas Edison began working on designing filament lamps in 1878. The filaments he used were initially made of platinum, a precious metal which is fairly easy to work and which has a high melting point. It wasn't perfect; the metal tended to absorb air as it heated up which weakened it, so the filaments had a relatively short life.

To overcome this problem he placed the filament inside a glass vacuum bulb. This improved the performance of the lamps but made them expensive. Platinum was also pricey; it had a similar value to gold, and its resistance was too low. This meant that if it was adopted commercially, a low-voltage system would have to be used, with thick copper cables.

Eventually Edison worked out that a bulb needed a high-temperature resistance of 100 ohms or more to restrict the size and cost of the distribution system.

However, since he was now using a vacuum bulb it meant he could try out carbon filaments. He tried using carbonised cotton thread (cotton impregnated with lampblack, a form of non-crystalline carbon), carbonised cardboard, carbonised paper, and various vegetable fibres similarly carbonised. Eventually after much research, testing about 6000 different biological materials, it was found that carbonised bamboo made the best filament, and this was eventually used in his commercial bulbs.

The world's oldest light bulb has been burning for 109 years. It is at Fire Station 6, in Livermore, northern California. It was designed by Adolphe Chailet, one of Edison's competitors.

You might be interested in these interesting novelty items available on Ebay, using modern-day replicas of Edison bulbs, also with carbon filaments. They are very eye-catching (click on the thumbnails):

replica edison lamp on Ebay.... replica edison lamp on Ebay....

The Ebay link for these items are link1 and link2

The person making these (not me!) puts another lamp online when one is sold. They are all hand-made (no two are quite the same) and can be found on Ebay using the terms:

carbon filament lamps edison

The bases are made of oak, smoothed and varnished. There is a small plaque on each, saying what it is; each one uses a 250V fitting which plugs into the mains. The light is very mellow, as shown in the first picture.


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