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These two electric lamps are examples of those with a copper threaded base with wood as the insulator, a collar above the base, and a carbonized split Japanese bamboo filament connected by copper plated clamps and screws.  (The earlier method of attaching the filaments to the inner leads by means of copper clamps and screws proved to be very cumbersome and unreliable and often resulted in broken filaments, cracked bases, and electric arcing.)  These two bulbs were manufactured in 1881.  Notice that the bulb on the left looks quite darkened.  This wasn’t an intentional coloring of the bulb. It actually displays black soot on the inside that was given off or “evaporated” by the carbonized filament as it glowed.  The soot migrated from the filament to the bulb’s interior surface on which it settled and later darkened the bulb.  Soot darkening was an annoying feature of a light bulb for many years as it reduced the bulb’s light output and shortened its otherwise useful life span.  It wasn’t until a General Electric scientist by the name of Dr. Irving Langmuir [see A49] in 1913 discovered a way to reduced the filament evaporation that the problem of soot darkening was solved.

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