GENERATION, CONTROL, AND MEASUREMENT 



173 



MERCURY ARC 



In the mercury-arc discharge lamp the distribution of energy into the 

 various excited states of the mercury atom is in part determined by the 

 vapor pressure. These lamps may be divided into three general classes 

 depending on the operating vapor pressure. The low-pressure lamps are 

 low-intensity sources in which most of the energy is in the ultraviolet 

 and the spectrum consists of relatively few sharp lines (Table 3-11). 



Table 3-11. Spectral Energy Distribution of Mercury-arc Lamps 



Lamp wattage and designation'' 



Wave length, rati 



Spectral band 



220-230 

 230-240 

 240-250 

 250-260 

 260-270 



270-280 

 280-290 

 2<.»0 300 

 300-310 

 310-320 



320-330 

 330-340 

 340-350 

 350-360 

 360-370 



370-380 

 380-400 

 400-410 

 410-430 

 430-440 



440-540 

 640-550 

 550-570 

 570-580 

 580-760 



Principal 

 lines 



254 

 265 



280 

 297 

 302 

 313 



365 



405 

 436 



546 



578 



Average watts radiated per 10 m^ 

 within wave band indicated 



" The H lamps have a high-silica glass tube inside a glass jacket; the UA lamp con- 

 sists of a single tube of quartz. 



