644 



DISPLAY SYSTEM DESIGN PROBLEMS 



100 



20 30 40 50 60 



PEDESTAL AMPLITUDE (Volts) 



70 



Fig. 12-25 Average Trace Brightness as a Function of Pedestal Amplitude and 

 Receiver Noise. 



for the additional brightness that must be generated by the electron beam 

 so that the observer can detect the spot at a given level of probability. 



Effects of Operator Environments. The data discussed in the 

 foregoing paragraphs are for normal conditions when the observer is not 

 under environmental stress such as acceleration and low atmospheric 

 pressures. These characteristics will change as acceleration and low 

 atmospheric pressure affect the operator. Fig. 12-27 shows the loss of 

 visual acuity as a function of acceleration and body position. A comparison 

 of the minimum spot size which can be resolved at 1 g (0.91 minutes of arc) 

 and that which can be resolved at 3 g (1.11 minutes of arc) indicates that 

 a 22 per cent increase in spot size is required for equivalent detectability 

 at high acceleration. 



The effect of low atmospheric pressure manifests itself as a lack of oxygen. 

 Fig. 12-28 shows the required oxygen at different altitudes to maintain 

 oxygen pressure in the lungs at sea-level conditions. 



