Metal halide lamp
In the early 1960s, people successfully added many metal halides to high-pressure mercury arcs, which improved the color of the lamp and greatly increased the luminous efficiency. This is because metal halides provide arc discharge with high vapor pressure, and metal atoms radiate with their own characteristic spectrum lines, filling the gap in the mercury spectrum line. There are two types of metal halide lamps produced in my country: tubular and spherical. The spherical ones have double-ended AC, DC and single-ended DC lamps.
Dysprosium lamps can be used as light sources for filming movies and television, with power ranging from 1kW to 10KW. The spherical ones can range from 250W to 3.5kW, with a variety of specifications. The commonly produced 400W or 1000W sodium thallium indium lamps are used for lighting. Various metal halide lamps can obtain special positive spectrum lines radiated by various metals. Therefore, many special uses can be obtained. It is particularly suitable as a photochemical light source. This is because the spectrum line can be freely selected and the luminous efficiency is high. It can be a point light source (spherical) or a linear light source (tubular), and the absolute intensity of radiation can be selected from the power size. However, it should be pointed out here that the spectrum and light effect of metal halide lamps will be affected by different tube wall temperatures (different cold end temperatures). Therefore, for the same lamp, its power control is different, and its radiation spectrum and intensity are different when the external conditions are different. Be careful when using it.
Indium iodide, thallium iodide, and lithium iodide can make blue, green, and red lights respectively. Thallium iodide (535nm) is a good light source for photochemical synthesis, underwater color television photography, and fishing. my country can produce high-power 10,000 to 50,000 watt thallium iodide lamps. Thallium iodide lamps (filled with a small amount of thorium iodide) can be used in the synthesis of nylon 66, and the photochemical reaction of benzene nitrosylation has achieved good results.
Gallium iodide and lead iodide can produce strong radiation in the wavelength range of 340 to 450nm. If it is used instead of a mercury lamp, the efficiency of photographic reproduction or photolithography can be increased by 50 to 100%. The spectrum of this lamp is shown in Figure 9-14. The application of gallium iodide lamps in the copying of microbubble film has achieved good results in place of mercury lamps and mercury Xenon Lamps. It not only ensures the concave density of the film, but also doubles the copying speed. The metal halide lamp using bismuth chloride can produce 2800~3200A, 3200~4200A ultraviolet rays, which can be used for photochemical reactions.
If the metal halide lamp adopts the glow discharge form, an excess of zinc or cadmium halide is filled in the arc tube to obtain 2800~3400A ultraviolet rays. For example: 400W, the inner diameter of the arc tube is 18mm, the distance between the two thorium oxide electrodes is 10cm, and 75mg of ZnCl₂ and 2666Pa (20mmHg) of Xe are filled. When 75V voltage is applied to the electrodes, a glow discharge with a current of 50mA can be generated. The lamp emits strong ultraviolet rays with a peak value of 3065A. In addition, the peak value of the emission spectrum may vary with the filling material. When zinc bromide is filled, the peak value is 3070, 3110A, and when zinc iodide is filled, it is 3280, 3320 A. When cadmium bromide is filled, when the lowest temperature of the arc tube is 600~700℃, the peak value is 3175A, when cadmium chloride is filled, it is 3080~3180A, and when cadmium iodide is filled, it is 2385, 3380A (at this time, the coldest temperature of the tube wall is 400~550°℃). Compared with high (medium) pressure mercury lamps of the same power, the ultraviolet output intensity of these lamps can be doubled. In short, various metal halides can emit the required light wave region (ultraviolet region) with different peak values in the arc, which can be used for photochemistry, which will greatly benefit the development of photochemistry.
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