These are examples of the first bulbs with a carbonized split Japanese bamboo filament and a copper threaded base developed by Edison in late 1880.
These bulbs may come with the wooden screw sockets with copper female threads inside
and a thumbscrew on the side of the socket for tightening the base inserted into the socket. Early carbonized split bamboo filaments were an improvement over the previous Bristol cardboard filaments as they lasted longer, about 600 hours. To obtain this type of filament, Edison had his team scoured the world for plant material that would make a superior filament than that of Bristol cardboard. He finally found the plant in 1880 from a species of Japanese bamboo plant scientifically referred to as Phyllostachys bambusoides
but otherwise known by its common name as “Madake.” These bamboo plants are indigenous to the country of Japan and, aside from making excellent lamp filaments, they also make excellent fishing rods. The filaments would be sliced from a length of a single bamboo into extremely fine strips, bent to their desired hairpin shapes in order to fit into the bulb, and then carbonized by first covering them with powdered carbon (to minimize the availability of oxygen) inside a crucible and then heating the crucible inside a furnace at an extremely high temperature for several hours before allowing them to cool. During this process, the bamboo strips would turn from its initial cellulose structure to a pure carbon structure, ready to be mounted in the glass bulbs with extreme care. However, the length of a bamboo filament was restricted as they could be no longer than the distance between the joints of the bamboo cane. This placed an upper limit as to how bright a carbon filament light bulb could be. These light bulbs burned not much brighter than did a candle. As for the base, it is recorded that Thomas Edison, while discussing with his team the need of a better way of attaching the light bulb to the electrical circuit, conceived the idea of a threaded base and socket while noticing an oil can resting on a nearby shelf. Edison removed the oil can from the shelf and unscrewed the cap off. After carefully examining the cap for a moment, Edison then exclaimed to the others, “This certainly would make up a bang-up socket for the lamp!” The threaded bases in each of the lamps shown each have two copper contacts (both the threads and the cone–shaped ring) constructed all over plaster of paris while the wooden screw sockets had the copper female threads and thumbscrews on the side to allow the bulb’s base to be inserted and tightened into place. This allowed the bulbs to be installed upside down from a ceiling if so desired or attached to a wall fixture. It was so successful and convenient that it has been in use to this very day.
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