4.74 FERREE AND RAND— LIGHTING 



lighting on the extrinsic muscles of the eye; the effect of the angle 

 at which the light falls on the work ; the effect of motion pictures ; 

 etc. Space can not be taken in this paper for a detailed report of 

 these investigations. For convenience of reference a complete bibli- 

 ography of the studies published up to the present time is appended 

 at the end of the paper. 



IV. Ocular Discomfort in Relation to the Position of 

 THE Source of Light in the Field of View. 



In addition to studying the conditions that give us maximal 

 visual efficiency or power to sustain clear seeing, it is important also 

 to determine the lighting conditions and eye factors that cause ocular 

 discomfort. Therefore, in case of each of the lighting situations 

 tested for tendency to cause loss in power to sustain clear seeing, 

 we have determined the tendency to produce ocular discomfort, as 

 has been noted in the preceding pages. In the work on the lighting 

 systems previously described, however, the effect of "the angle of 

 presentation of surfaces of high brilliancy (lamp, surfaces and 

 openings of reflector, ceiling spots, etc.) on both the power to sus- 

 tain clear seeing and the tendency to produce ocular discomfort was 

 shown through a comparatively small range of variation of angle. 

 It was thought advisable to supplement this work by determining 

 the effect on the tendency to produce ocular discomfort for a wider 

 range of variation of angle of presentation. For this purpose a 

 large perimeter was used, along the arm of which the brilliant sur- 

 face, the effect of which was to be determined, could be moved. A 

 variable area of brilliant surface was obtained by mounting on the 

 arm of the perimeter a lamp house in the side of which next to the 

 observer's eye a large iris diaphragm was inserted. The brilliancy 

 and color value of this test surface could be varied within limits to 

 suit the needs of the experiment by means of absorption screens and 

 filters. Larger variations of intensity were obtained by means of the 

 use of lamps of dift'erent wattages. The arm of the perimeter could 

 be shifted to any meridian in which it was desired to work and the 

 lamp could be moved at will along the arm. W'orking in this way 

 it is possible to investigate the eft'ects of many types of distribution 



