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Materials used to make light sources
Lamp materials can be divided into three categories:
(1) Glass and ceramics: (2) Metals: (3) Gases and vapors.
In order to isolate the interior of the lamp from the surrounding air and maintain the gas atmosphere in the bulb, most lamps use a transparent glass bulb. Therefore, the performance of the glass bulb must be compatible with the filling gas and other parts of the lamp in order to withstand the pressure and temperature at the time of ignition. After gradual development, there is now a series of bulb materials ranging from low-melting-point glass to high-temperature resistant transparent ceramics.
Tungsten has become the most important metal material for lamps, mainly because it has a high melting point, high mechanical strength, and can produce a low vapor pressure at the normal operating temperature of the lamp. The main use of tungsten is to make electrodes for discharge lamps and filaments for incandescent lamps. Some people have proposed to replace tungsten with certain oxides and carbides, but no progress has been made so far. Molybdenum is generally used to make internal parts such as leads and filament brackets. There are many other metals, including some rare metals, which are also indispensable materials for the lamp industry.
The filling gas in the lamp has two obvious functions. The inert gas in the discharge lamp can cause gas discharge and also play a buffering role when metal vapor becomes the main medium of the discharge. The gas filled in the incandescent lamp can inhibit the evaporation of the filament, which has a great impact on the light efficiency and life of the lamp. Therefore, it is also necessary to understand the physical properties of commonly used lamp-making gases.
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