English: A General Electric tantalum incandescent light bulb from 1908, 100 V, 44 watts. Refractory metal filaments began to replace the Edison carbon filament in light bulbs around the turn of the century, because they lasted longer and used less energy. Tantalum was the first widely used metal filament, which briefly took over before the more durable tungsten filament was developed. Siemens developed the tantalum lamp in 1902 and GE bought the rights to it and produced them until 1913. Several feet of filament were needed per bulb and the filament wire wasn't double-coiled as modern filaments are, requiring the elaborate support structure seen. The filament contracted during use, so the bulb was made with slack loops of filament which tightened during use. The tantalum lamp had an efficiency of 2 watts per candle, 35% better than the 3.5 watts per candle of carbon. On DC it had a life of 800 hours, but its life was much shorter on AC, and the spreading use of AC distribution systems doomed it.