12-7] IMPORTANT CHARACTERISTICS OF THE HUMAN OPERATOR 643 



Spot Brightness 

 1.27 Foot Lamberts 



Background Brightness 

 (Foot Lamberts) 



40.5 



40 



50 



60 



70 



A6/£ 



Fig. 12-24 Detection Time as a Function of Contrast, Target Brightness, and 

 Background Brightness (Light Adaptation Duration 120 sec at 3100 ml). 



brightnesses as a result of his other duties, time will be lost in target 

 detection even if the target is present on the scope. It is obvious from these 

 figures that the system designer must consider these additional duties in 

 the development of his system. 



A study typical of those often required in the development of the display 

 system concept has been performed by Gardner and Carl.'' In this study, 

 the experimenters were interested in determining whether there exists an 

 optimum pedestal amplitude voltage as a function of the ambient brightness 

 and the receiver noise. (The pedestal amplitude voltage is used to set the 

 trace brightness on intensity-modulated radar scopes. This brightness is 

 independent of the brightness that is incident to the receiver noise on the 

 signal.) Fig. 12-25 shows the relationship between pedestal amplitude 

 voltage, receiver noise, and trace brightness. Fig. 12-26 shows detectability 

 as a function of pedestal amplitude voltage, receiver noise, and ambient 

 light levels. Using the data shown in Figs. 12-26 and 12-21, it is possible 

 to determine the contrast that was obtained at the detectability threshold 

 for each pedestal amplitude voltage and receiver noise level. In such 

 instances the trace brightness can be considered to be equivalent to the 

 background brightness shown in Fig. 12-21. With this information and a 

 measure of the ambient brightness, it is possible to state the requirements 



■^R. E. Gardner and J. M. Carl, The Effects of Ambient Illumination, CRT Bias, and Noise 

 upon Target Detectability with a B-Display, NRL Report 5264, Jan. 28, 1959. 



