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BELL SYSTEM TECHNICAL JOURNAL 



path of the arc light beam, and potassium photoelectric cells specially 

 sensitized to blue light and more sensitive than those previously 

 used have been developed. The number of these cells and their area 

 has also been increased over those used in the earlier television 

 apparatus so that the necessary intensity of the scanning beam is 

 decreased. 



The second half of the problem, namely that of securing a max- 



Fig. 3 — Interior of the television booth. 



imum intensity of the neon lamp, has been attained by the develop- 

 ment of water-cooled lamps capable of carrying a high current. 

 The net result of the use of the blue light for scanning, of more 

 sensitive photoelectric cells, and of the high efficiency neon lamps is that 

 the user of the apparatus is subjected only to a relatively mild blue 



