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A deuterium arc lamp (or simply deuterium lamp) is a low-pressure gas-discharge light source often used in spectroscopy when a continuous spectrum in the ultraviolet region is needed. Plasma "arc" or discharge lamps using hydrogen are notable for their high output in the ultraviolet, with comparatively little output in the visible and infrared. This is similar to the situation in a hydrogen flame. Arc lamps made with ordinary light-hydrogen (hydrogen-1) provide a very similar UV spectrum to deuterium, and have been used in UV spectroscopes. However, lamps using deuterium have a longer life span and an emissivity (intensity) at the far end of their UV range which is three to five times that of an ordinary hydrogen arc bulb, at the same temperature. Deuterium arc lamps, therefore, despite being several times more expensive, are considered a superior light source to light-hydrogen arc lamps, for the shortwave UV range. ==Principle of operation== A deuterium lamp uses a tungsten filament and anode placed on opposite sides of a nickel box structure designed to produce the best output spectrum. Unlike an incandescent bulb, the filament is not the source of light in deuterium lamps. Instead an arc is created from the filament to the anode, a similar process to arc lamps. Because the filament must be very hot before it can operate, it is heated for approximately twenty seconds before use. Because the discharge process produces its own heat, the heater is turned down after discharge begins. Although firing voltages are 300 to 500 volts, once the arc is created voltages drop to around 100 to 200 volts. The arc created excites the molecular deuterium contained within the bulb to a higher energy state. The deuterium then emits light as it transitions back to its initial state. This continuous cycle is the origin of the continuous ultraviolet radiation. This process is not the same as the process of decay of atomic excited states (atomic emission), where electrons are excited and then emit radiation. Instead, a molecular emission process, where radiative decay of excited states in molecular deuterium (D2), causes the effect. The spectral line structure of deuterium does not differ noticeably from that of light hydrogen, but deuterium has a slightly stronger molecular bond (439.5 vs. 432 kJ/mol) and is less-well ionized at the temperature of the arc, and this causes a larger population of molecules and a greater emissivity (light output) of UV in the molecular part of the spectrum that is farthest into the ultraviolet.〔(Paper on UV analysis which describes deuterium lamp advantage ) Accessed Sept 25, 2014.〕 Because the lamp operates at high temperatures, normal glass housings cannot be used for a casing. They would also block UV radiation. Instead, a fused quartz, UV glass, or magnesium fluoride envelope is used depending on the specific function of the lamp. The typical lifetime of a deuterium lamp is approximately 2000 hours (Most manufacturers guarantee 2000 hours, but newer lamps are consistently performing well out to 5000 hours and more). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Deuterium arc lamp」の詳細全文を読む スポンサード リンク
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