01 I 10 100 1000 



LUMINANCE OF SMALL AREA IMMEDIATELY AROUND THE TEST OBJECT 

 ( IN EQUIVALENT FOOT-CANDLES ) 



Fig. 23. Visual acuity as a function of the luminance of the small area immediately around the test 

 object with three different surround luminances. The luminance of the surround could not be made to 

 match that of the task at the two highest luminance levels. These are average data for two subjects. 

 (Data from Lythgoe, 62) 



GDI 



100 



LUMINANCE OF LARGE AREA SURROUNDING THE VISUAL TASK 



IN EQUIVALENT FOOT CANDLES 



Fig. 24. Visual acuity as a function of surround luminance with the luminance of the small area 

 around the visual task held constant. These are average data for three subjects. (After Lythgoe, 62) 



33 



