APPLICATIONS AND SOUHCES OF ULTKAVIOLET 87 



HIGHER PRESSURE MERCURY SOURCES OF ULTRAVIOLET 



Electric-discharge mercury lamps in tubes of high ultrav^iolet trans- 

 mission develop relatively full-line spectra when operated at higher 

 (over 400 mm or 0.5 atm) pressure. The total ultraviolet per watt of 

 electrical input drops to about one-half that of a low-pressure lamp in 

 tubes of the same transmission. The energy is distributed variably 

 among about 20 lines instead of being almost entirely concentrated at 

 2537 A, as shown graphically in Fig. 2-5. Lines other than 2537 A of 

 good energy content become very useful for studies of biological effects 

 as functions of wave length. The high intrinsic output of the higher 

 pressure sources becomes essential for effects requiring ultraviolet inten- 

 sities unobtainable even at the surface of the low-pressure sources. 

 High-pressure lamps in the lower wattage sizes are essential to any 

 research involving isolation of spectral lines or bands by optical methods. 

 Their adaptability can be inferred from the source dimensions given in 

 Tables 2-3 and 6, based partially on the lES Lighting Handbook, 2d ed 

 (1952). 



INTENSITY AND VARIATIONS WITH DISTANCE 



The radiant-energy intensity at a distance of 1 meter, in microwatts 

 per square centimeter, can be approximated from the total watts output 

 rating of Table 2-6 by multiplying by a factor of 10. Conversion to 

 other units and distances can be made by the methods outlined for low- 

 pressure sources. 



INDIVIDUAL LINE INTENSITIES 



Persons who need a more detailed analysis of the line spectra of the 

 sources listed in Tables 2-3 and 6 but who do not have facilities for making 

 line-intensity measurements under the actual conditions of their experi- 

 mentation should correspond directly with manufacturers of the source 

 being used. The relative energy distribution among the lines of high- 

 pressure mercury lamps varies between individuals and between groups 

 in such a complicated fashion that no general rules can be given and 

 detailed listings here become impractical. A fairly representative high- 

 pressure spectrum is shown graphically in Fig. 2-5 and is typical of such 

 lamps as the UA-3 and UA-1 1 of Table 2-6. 



STARTING AND RESTARTING TLMES 



With few exceptions, the higher pressure lamps start with low-pressure 

 characteristics and require 3-5 min to reach normal operating temper- 

 ature, pressure, and radiation output. If momentarily extinguished, they 

 also require a cooling and restarting period equal to or in some cases 

 one-half longer than their warm-up time. 



