The Coolidge Process for Making Tungsten Ductile: The Foundation of Incandescent Lighting

Abstract

Try to imagine a world without incandescent lamps. We light our homes with 20-200-watt lamps, which are routinely purchased in local stores. These lamps are made at the rate of millions per week and their manufacture represents a large global industry. The consumer expects them to last approximately 1,000 hours and to be energy efficient and inexpensive.Many types of incandescent lamps exist. Figure 1 shows several examples. The most common types are A-line (the general household lamp), automotive lamps, and reflector lamps for floodlight or projector applications. We also have many thousands of specialty lamps, which have a broad range of applications, such as audio-visual projectors, fiberoptic systems, video-camera lights, airport-runway markers, photoprinters, medical/scientific instruments, and stage/studio systems. They can have power ratings from a few watts to several thousand watts, but they all have at least one feature in common. They contain a filament made of tungsten wire. The diameter of the wire will vary, depending on the power rating and application of the lamp, but for most common household lamps it is less than 100 μm.