( 3 ) the spectral matching factor of nea phothocathodes for reflecting spectrum of objects under night sky radiation has been studied . the spectral matching factors of typical phothocathodes , such as gaas nea photocathode , s _ ( 251 ) and s _ ( 252 ) photocathode , are calculated and compared . the factors give the explanation of high detection performance of the low - light - level night vision equipments
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