640 



DISPLAY SYSTEM DESIGN PROBLEMS 



response of the fovea and the periphery to energy. The periphery response 

 is indicated by the curve labeled scotopic, while the foveal response curve is 

 labeled photopic. The ordinate of Fig. 12-19 is a measure of the energy 

 required to obtain an equal brightness response as a function of wavelength. 

 For example, referring to the photopic curve, a greenish-yellow hue (550 

 mM) will require approximately 20 per cent of the energy required by an 

 orange hue (650 mju) to elicit an equal brightness response. 



Although the terms periphery (photopic) and fovea (scotopic) have been 

 used to designate the parts and response of the eye, there has been no 

 discussion as yet of the quantitative levels of energy at which these two 

 parts of the eye become effective. Fig. 12-20 gives a crude practical 

 estimate of the brightness at which the fovea and the periphery become 

 effective. The periphery begins to be effective at about 0.1 millilambert, 

 depending upon the length of dark adaptation. 



-3-2-1 1 2 

 Log, (,6 {foot lamberts) 



-3-2-1 1 2 3 

 Log,„B (foot lamberts) 



PERFORMANCE LEVEL 



95% 50% 



-3-2-1 1 2 

 Log JO B (foot lamberts) 



PERFORMANCE LEVEL 

 95% 50% 

 5 



-3-2-1 1 2 3 

 LogjoB (foot lamberts) 



Fig. 12-21 Contrast Value for a Given Detection Probability as a Function ot 

 Performance Level, Time of Exposure, Background Level, and Spot Size. 



