Lamp life

These detectors are often used to detect components of a fluorescent derivative prepared to increase the detection sensitivity of compounds with poor UV absorptions. Both variable and filter variable, fixed-wavelength fluorom-eters are available for HPLC, with the same limits of lamp life and sensitivity seen in comparable UV detectors. 

Any emitting surface, cold-cathode, hotdevelop vapor pressures from the elements/compounds of their construction when heated. These vapors will also manifest themselves particularly during the initial start-up (breaking in) time of the lamp. Early atomic absorption, multi-element lamps were shown to have this problem. Some of these additives specifically react with residual gases and elements that might have a deleterious effect on lamp life. The electronics industry has used what are called "getter" substances in their tubes to remove some of these substances and improve emission. 

Many detectors track the number of hours the lamp is ignited. Although the lamp life may vary, the detector s meter reading can be a helpful guide for troubleshooting. Lamps can sometimes operate for more than 2000 h. To distinguish a lamp problem from air bubbles, one should stop the mobile phase flow. A lamp problem will persist when the flow is stopped, whereas, if the problem is due... 

Advantages Higher germicidal efficiency, nearly all ontput at 254 nm smaller power draw per lamps Longer lamp life Higher power output fewer lamps for a given application smaller reactors... 

Disadvantages More lamps needed Higher operating temperature can accelerate fouling shorter lamp life lower electrical to germicidal conversion efficiency... 

Lamps produced during the past two years, for all but a few particularly recalcitrant elements, have shown such long life that it has been all but impossible to gather statistical data on failure rates. For example, if one determination per minute is made on a double-beam instrument which does not expend any lamp life in warm-up, a 500-hour performance corresponds to 30,000 determinations. 

For some elements, better alloy combinations have been found which make it possible to use higher lamp currents with no sacrifice of lamp life. 

Usually phosphors decline slowly during lamp life [2]. This can be due to several processes ... 

The phosphors in the tricolor lamp show another advantage over the halophosphate phosphors, viz. a much better maintenance during lamp life. In Fig. 6.IS the output decrease after 2(KX) hours of burning is plotted as a function of the wall load. The higher stability of the rare-earth activated phosphors is translated into a higher maintenance. The value of the wall load is determined by the tube diameter (see Fig. 6.18). Tricolor and Special Deluxe lamps are now available in a tube diameter of 25 mm, to be compared with the 36 mm of the halophosphate tube. It even proved to be possible to reduce the tube diameter to 10 mm. With this small diameter the discharge tube can be fold up and the compact luminescent lamp is bom. 

Tungsten Halogen Lamp - A type of incandescent lamp that contains a halogen gas in the bulb, which reduces the filament evaporation rate increasing the lamp life. The high operating temperature and need for special fixtures limits their use to commercial applications and for use In projector lamps and spotlights. 

FIGURE 16 The basic elements of a flash lamp. The envelope is typically made from fused silica, the electrodes from a tungsten alloy. The shape of the cathode helps to increase lamp life. 

A greatly reduced lamp life (/.e., less than 100h) can be caused by differential cooling of the electrodes. The aluminium tubing supporting the silica shielding as shown in Fig. 16-3 is intended to prevent cooling of the lower end of the lamp. 

The selection of the source of light appropriate to the circumstances depends on several factors. It is important to consider efficiency, ease of installation, costs of installation and running, maintenance, lamp life characteristics, size, robustness and heat and colom output. The efficiency of any lamp (often termed efficacy) can be expressed in terms of light output per unit of electricity used (lumens per watt). Generally speaking, incandescent lamps are less efficient than discharge sources. 

Optimum lamp life 2,000 h. Operating costs calculated on the basis of 90% COD removal. 

The SON lamp is suitable for many applications. Because of the warming glow of the illuminance it is used in food halls and hotel reception areas. Also, because of the high efficacy and long lamp life it is used for high bay lighting in factories and warehouses and for area floodlighting at airports, car parks and dockyards. 

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