408 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



To watch a night mission return to blacked-out Britain or to see 

 hundreds of gliders sweeping into unlit cornfields during an airborne 

 maneuver, is to appreciate how unnatural such duties are to the boy 

 who has grown up with an electric-light switch at his finger tip and 

 a flashlight in his pocket. Even the flight surgeon has had to recall 

 forgotten facts concerning the mechanism of night vision: the fact 

 that the cone cells of the retina, which are used in day vision, do not 

 respond to dim lights; that the rod cells, which are used in night 

 vision, are located in the peripheral regions of the retina, so that one 

 sees a dim object best by looking a little away from it; that the sensi- 

 tivity of the rods is destroyed for some time by a bright light, and is 

 least affected by red of all the colors. The translation of these prin- 

 ciples into tactical practice is an important element in the success of 

 night operations. 



A first step toward this end was a revision of lighting practice on 

 airfields and in aircraft. Dark adaptation following prolonged expo- 

 sure to bright light requires about half an hour, and until then night 

 vision is below normal. Accordingly, a pilot who goes quickly from 

 a lighted room into combat is relatively blind and under a severe 

 handicap. He is likewise at a disadvantage on looking from his 

 lighted instrument panel out into the darkness where enemy planes 

 are hidden. To protect the airmen against these hazards, the Air 

 Surgeon has recommended that lights to which the fliers are exposed 

 shall be red in color, whenever that is possible. As has been said, 

 this makes possible cone vision without affecting the subsequent sensi- 

 tivity of rod night vision. 



A more far-reaching effort to improve human efficiency in night 

 combat is the establishment of a night visual training program. Fol- 

 lowing the pattern of the altitude training program, the Army Air 

 Forces have developed a course of instruction which will familiarize 

 the airmen with basic physiological principles relating to night vision; 

 will warn him of the harmful visual effects of unnecessary light, of 

 diets inadequate in vitamin A, and of insufficient oxygen. To this is 

 added several hours of directed practice in the detection and identifi- 

 cation of faintly illuminated objects. We have reason to believe that 

 it is thus possible to improve visual performance in night operations 

 by as much as 30 to 40 percent. 



Just prior to our entrance into the war the National Research Coun- 

 cil sponsored a survey of the sensitivity of rod vision in a group of 

 several thousand military personnel. The results confirmed Hecht's 

 laboratory findings that, within a normal population, some individuals 

 are 15 times better fitted by their retinal characteristics for night 

 observation than the poorest, and 5 to 10 times better than the average. 



