90 



KADIATION HIOLOCJY 



;i\:iihil)l(' as arc also similar ijotassiuin and sodium lamps. Xoiic ol llicm 



arc, howcx'cr, sources of ult i'a\'iolct. ol the \va\'c lcnti;llis jicncially desired 



in biological work. 



SUN I,. \ MI'S 



Commercial sunlamps have been used for some biological research. 

 They provide energy down to 2800 A from sources of sufficiently high 

 intrinsic intensity to adapt them to optical methods of isolating narrow 

 spectral regions. They have the general characteristics of high-pressure 

 quartz-mercury arcs with the radiation limited to about 2800 A by the 

 enclosing bulbs or tubes. Laboratory housings for the S-4 lamp have 

 becMi comnKM-cially available. Lamp ('II-3 of Table 2-6 is proving more 



2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400 



WAVE LENGTH, A 



Fig. 2-19. Relative energy distril)uti()ii of fluorescent and S-4 type .sunlamps. 



useful in the same devices because it provides essentially the full (|uartz- 

 arc spectrum. Table 2-7 permits comparison with sources of Tables 2-3 

 and 6. Figure 2-19, which shows the relative energy distribution of sun- 

 lamps, is comparable with Fig. 2-5. The S-1 lamp spectrum is similar 

 to that of the S-4 but with addition of a continuous visible and infrared 

 spectrum from a tungsten filament in multiple with the mercury arc and 

 operating at a temperature of about 2000° K. The RS spectrum has 

 similar visible and infrared components from a tungsten filament in series 

 with the arc. 



As indicated in Fig. 2-19, tluorescent sunlamps provide a continuous 

 ultraviolet spectrum with a peak at about 3100 A. Mercury-arc lines 

 transmitted by the phosphor make an insignificant addition to it. The 

 generated energy in these lines is comparable with that in the lines of the 

 germicidal lamp and is transmitted to an extent of 60-70 per cent by the 

 phosphor. Although the low emission intensity of these lamps makes 

 them unsuitable for use with optical isolating systems, they are compara- 

 ble with the high-pre.ssure mercury arcs for low-intensity general irradia- 

 tion with energy of wave lengths in the 3000-3200 A range. They are 



