120 



RADAR SCOPES 



Color of Illumination 



The color of illumination has been alluded 

 to above, and relevant data from Williams 

 and Hanes (56) are given in Fig. 8. At very- 

 low illuminations color is certainly insignifi- 

 cant. At moderate levels, near that of the 

 scope, and at higher levels, there appear 

 to be very small but rather consistent dif- 

 ferences in favor of the shorter wavelengths. 

 Whether any practical advantage could be 

 gained from colored illumination in radar 

 operating rooms is dubious; it would at best 



well be sizeable "emotional" effects of color 

 which might affect extended work if not 

 thresholds. Qualitative observations of pips 

 under colored illumination suggest that there 

 may also be some pecuHar perceptual-con- 

 stancy effects. For further work on color, 

 the reader is referred to the Eastman-Kodak 

 report (58) and to Ferree and Rand (13). 



Filters 



Because of practical interest in the matter 

 it may be mentioned that unpublished data 



-10 



001 



005 01 05 



AMBIENT ILLUMINATION (FOOTCANIDlES) 



Fig. 8. Visibility and ambient illumination 

 Relative loss in visibility as each illuminant is increased from 0.02 ft-c, taken as a reference. Ac- 

 tually, any of the illuminants was ^ to 1 db better than darkness in intensities up to about 0.1 ft.-c. 

 Scope brightness is about 0.1 ft.-L. (optimal bias). Conditions: 7BP7 tube; 2 /zs x 2° pip; no video 

 noise. 



be very small. Certainly one would ex- 

 pect no differential effect on thresholds merely 

 of colored reflecting surfaces near by, such 

 as wall paint or paper. As an academic 

 question, the effect of color of illumination 

 is more interesting because it still is largely 

 an enigma. Most experiments have shown 

 either no effect or no consistent effects of 

 color unless the visual task itself is one of 

 discriminating colors, as in making color- 

 matches of dyes and fabrics. More work 

 in this area certainly is needed, for there may 



of the writer's show no very sizeable decre- 

 ment in visibility when a sheet of ordinary 

 plexiglass is put over a PPI scope. With 

 negligible ambient illumination, the mean loss 

 with clear plexiglass was 1.4 db and the 

 mean loss with an amber plexiglass, the kind 

 used for Navy scopes, was 2.0 db. The 

 loss was slightly less when ambient light 

 was increased. 



Treated filters, i.e., plexiglass with a fluor- 

 ide coating evaporated on the surface, were 

 also tested by comparing them with un- 



