Copyright 2005 Frank Andrews - Home - Lightbulb Index - Contact Email: Frank
A Short History of Electric Lightby Frank Andrews |
Edison, being a shrewd businessman, patented every idea he had even if he did not intend to follow it up. On the 10th of November 1879 he applied for a British patent for an incandescent lamp with a carbon filament in an exhausted glass bulb. The 1882 launch of Swan United Electric Light Company Limited brought Swan’s invention to Edison’s notice. Edison brought an action against Swan’s company for infringing his patent, whose response to this was that the Edison patent was invalid. Swan held patents which blocked Edison from progressing with his own inventions and in 1883 the pair settled out of court. They formed a new company the Edison and Swan United Electric Light Company Limited in 1883. A mitigating factor must have been the dozens of other light bulb makers that started to appear. By merging their companies they succeeded in achieving a virtual monopoly for the manufacture of the light bulb on the strength of their combined patents. This monopoly continued until Edison’s patent expired in 11th November 1893. They fought and won major court cases defending their patents in 1886 and 1888. These provide much of the evidence for Swan’s lead in developing the light bulb. The account of Henry Morton, a president of the Steven’s Institute of Technology and a friend of Edison, shows that Edison did not start work on the incandescent lamp until 1878. Neither Swan nor Edison had much involvement with the metal filament lamps that began to appear at the turn of the century but they certainly got involved after the discoveries. When the Edison patent expired the price of light bulbs plummeted by 60% and with more efficient gas lighting the price was to fall still lower by the end of the century.
The only major competitor to beat the EdiSwan patents was the light bulb of Hiram Maxim, Hiram Stephen (US & UK)Maxim. His distinctive ‘M’ shaped filament was sufficiently different to fall outside of the scope of the Edison-Swan patents. Sir William Crookes also produced an ‘M’ shaped filament but it was more fragile than Maxims and did not achieve the same success.
Tamodine was developed by Swan and his method of manufacture was described earlier. For the larger scale production an improved method was developed and adopted by most manufacturers of carbon bulbs. The use of Tamodine is shown in this description of ‘Glow Lamp’ manufacture of the 1890’s, this method would have been used by most light bulb makers with minor variations at this time.
Tamodine, a form of cellulose that has had the nitrous elements removed from it, was extruded into sheets. These were cut into fine strips and packed in bundles with carbon powder into ‘U’ shaped iron moulds and sealed. They were then heated in a furnace until white hot. When the moulds had cooled and were opened the strips had taken on the appearance and properties of metal. They were highly elastic and could be stretched straight without breaking. They were then fitted into special clamps that held them near both tips. Then they were immersed into boiling petroleum-oil and a large electric current was passed through the tips. This caused a thickening of the carbon at the tips which was needed to connect them. Platinum wires with a cup formed at one end were coated with molten glass to give a strong support. The thickened filament tips were fitted into the cupped wire ends which were then closed. The rods were fused to the glass base and the completed element assembly inserted into the hand blown bulb and fused together. At the top of the bulb a small glass tube was fitted to a vacuum pump by a rubber tube and simultaneously a current was passed through the element to assist the evacuation. This would take several hours and when sufficient air had been removed the tubes were sealed by melting forming the characteristic pip. By the 1890’s most manufacturers fitted a brass or ceramic cap to the base at this stage.Back to previous page