Discharge lamp maintenance

A serious drawback of this Mn phosphor is its poor maintenance in a lamp. It easily picks up mercury from the gas discharge and is liable to decompose under ultraviolet radiation. In addition beryllium is highly toxic [7], and nowadays not acceptable for application. In 1948, these phosphors were replaced by one phosphor with blue and orange emission, viz. Sb - and Mn -activated calcium halophosphate. 

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. 

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. 

In any choice between incandescent and the other types of lamp the total lighting costs must take into account not only running costs but also installation and replacement costs. Incandescent lamps are much cheaper to buy and install, they give out light immediately they are switched on and they can be dimmed easily, but tiiey are more expensive to run and have short lives, thus increasing maintenance costs. High pressure discharge... 

Mercury. While mercury lamps used to be the standard in high-intensity discharge lighting, their time has passed. This technology has too many drawbacks low LPW, low CRI, poor lumen maintenance, and a blue light that has questionable appeal. In the next 5 to 10 yr, expect sales of mercury lamps to virtually evaporate. 

Varta supply a non-sealed double cell (DTN) for portable lamps. This battery is available in a capacity range 4.5-11 Ah (Table 51.46). It has a light weight, even voltage level, good capacity, long service life, lack of maintenance and low self-discharge rate. 

---