Electrodeless lamp

In general, the electrodeless lamp contains a small amount of mercury and a neutral starter gas. The mercury pressures during its operation are in the 5-20 bar range, which is higher than for arc lamps, with pressures only in the 1-2 bar range. The characteristics of fhe lamp can be modified by fhe addition of mefal halides in confrolled quanfifies to the gas. The frequently used D or V lamps contain iron or gallium salts, respectively. Some characteristics of microwave-powered lamps are in Table 3.1. 

A variefy of gas fills are available, and fhese cover a fairly large range of UV and visible specfra. The bulbs are interchangeable and can be changed easily, so if is easy to use the proper lamp for a specific job. The advanfages of fhe elecfrodeless lamp systems are  

Lamp System Bulb Type Bulb Diameter, mm Peak Irradiance, W/cm (UVA) 

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The operating conditions affecting electrodeless lamp performance are a combination of many factors [30] ... 

The microwave photochemical reactor is an essential tool for experimental work in this field. Such equipment enables simultaneous irradiation of the sample with both MW and UV/VIS radiation. The idea of using an electrodeless lamp (EDL), in which the discharge is powered by the MW field, for photochemistry was bom half a century ago [46, 68]. The lamp was originally proposed as a source of UV radiation only,... 

Simultaneous application of UV and MW irradiation has found widespread use in industry. The techniques are based on the conventional UV lamps and MW-powered electrodeless lamps and MW devices [28], The following paragraphs discuss several patents and papers that describe industrial microwave photochemistry, such as treatment of waste water, sterilization, or industrial photo induced organic synthesis. 

In the method described by Willie et al. [167] atomic absorption measurements were made with a Perkin-Elmer 5000 spectrometer fitted with a Model HGA 500 graphite furnace and Zeeman effect background correction system. Peak absorbance signals were recorded with a Perkin-Elmer PRS-10 printer-sequencer. A selenium electrodeless lamp (Perkin-Elmer Corp.) operated at 6W was used as the source. Absorption was measured at the 196.0nm line. The spectral band-pass was 0.7nm. Standard Perkin-Elmer pyrolytic graphite-coated tubes were used in all studies. 

In general, the electrodeless lamp contains a small amount of mercury and is filled with a neutral starter gas. The mercury pressures during its operation are in... 

Flydrides, which are easily thermalised at around 1000 K, liberate the atoms of an element. An electrodeless lamp is preferably used as a light source. 

One of the disadvantages of electrode lamps is that they take about 3 min to warm up from a cold start and about 5 min to restart after being turned off. Electrodeless lamps need no more than 15 s to come to full power from a cold start or 60 s from a hot start. This hot start time can be reduced to instant starting (less than 1 s) if required. Presumably this would alleviate the need for shutters on commercial curing lines. 

The elimination of glass-metal seals results in a simpler, less stressed bulb. As a result, the electrodeless lamp potential lifetimes should be superior to the electrode type. In fact, a mechanism for failure has not yet been identified. 

Because the electrodeless lamp can be cooled uniformly, it can be made to run cooler than the electrode type, but at the same time it can be driven at higher power. This allows for lamp input powers up to 600 W/in. as compared to the conventional 200 W/in. of electrode lamps, without any serious degradation of lamp lifetime. Because the plasma inside has a higher electron temperature, the spectrum is shifted further toward ultraviolet. With the same fill, the same lines and continuum appear as with an electrode lamp but the output in the UV is much greater. The actual UV output from a 320 W/in. electrodeless lamp is 117 W/in. This represents a 36% energy efficiency as compared to about 20% for 200 W/in. electrode arcs. Of course, it must be added that considerable energy losses occur in converting ac to radio frequency. 

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