Edison Created a Long-Lasting Incandescent Light Bulb Using Carbonized Bamboo Filament
The invention of the incandescent light bulb by Thomas Alva Edison illuminated homes around the world. Edison began experimenting with incandescent bulbs in 1878. These bulbs produce light by passing electricity through a thin material filament until it heats up enough to glow. Many inventors had sought to perfect the incandescent bulb, but the bulbs they created had very short lifespans. Other types were too expensive for large-scale commercial production, while remaining types consumed a lot of electricity and required thick filaments, leading to increased costs. Finding a suitable material for light bulb filaments was a significant challenge that Edison overcame, according to Interesting Engineering.
Bamboo growing near Iwashimizu Hachimangu Shrine in Kyoto. (Photo: mTaira)
Edison realized that to maintain the electric current, he needed to find a material with high resistance. To extend the lifespan of the filament, the material also needed to be durable enough to withstand heating. After testing thousands of materials from platinum to animal hair, Edison discovered that carbon filaments possessed the characteristics he was looking for. He decided to try filaments made from carbonized cotton fibers. This bulb lit up for a record-breaking 14 hours. Edison immediately applied for a patent, describing that the carbon filament could be made from various materials such as “cotton, flax fibers, wood strips, and paper, rolled in different ways.”
Edison continued to experiment with several other organic materials, carbonizing them in the laboratory. He reached out to biologists and requested samples of various plant fibers from tropical regions. He sent staff around the world in search of the perfect material. Edison estimated that he had “tested no less than 6,000 plant species, scouring the globe for the most suitable filament material.”
One of Edison’s assistants, William H. Moore, sent him a sample from a bamboo species growing near the Iwashimizu Hachiman Shrine in Kyoto in 1880. This plant, scientifically known as Phyllostachys bambusoides, is native to China and Japan, where its hollow stems are used for making flutes and crafts. Bamboo also makes for excellent fishing rods. Edison himself had seen such rods during a fishing trip in Wyoming two years prior, where he had tested some fibers taken from bamboo fishing rods. It is unclear whether Edison specifically requested Moore to send that particular bamboo species or if Moore sent the sample independently. Regardless, Edison discovered that carbonized bamboo made excellent light bulb filaments.
To produce these filaments, the bamboo is split lengthwise into very fine strips and bent into a U-shape or closed circuit to fit into the bulb. They are then coated with carbon powder and heated in a furnace at extremely high temperatures for several hours, after which they are allowed to cool. Throughout this process, the bamboo strips transform from their original cellulose structure into pure carbon, ready to be placed inside the glass bulb. However, the length of the bamboo filament can only be as long as the distance between two nodes of the bamboo. This limits the filament’s length and thus sets a cap on the brightness that the carbon filament bulb can achieve. The bulbs made from carbonized bamboo filaments are not much brighter than candles but last significantly longer than any filament available at that time. Some bulbs created by Edison and his team lasted over 1,200 hours.
Carbon filaments became the standard material for incandescent lamps until researchers developed tungsten filaments, which allowed bulbs to last longer and shine brighter. Tungsten incandescent bulbs were produced by a Hungarian company named Tungsram in 1904. In 1911, Edison’s company, General Electric, also switched to using tungsten. Edison passed away in 1931.
