JULT 17, 1914] 



SCIENCE 



85 



for the momentary judgment or the highest 

 level of efficiency for the fresh eye. It is 

 rather the one that gives us the least loss of 

 efficiency for a period of work, and the maxi- 

 mum of comfort. 



In 1911 the American Medical Association 

 appointed a committee to study the effect of 

 different lighting systems on the eye. The 

 vpriter was asked to share in the vrork of this 

 committee. The problem presented to him 

 was to furnish tests that would show the ef- 

 fect of different lighting systems on the eye, 

 and more especially to devise, if possible, a 

 test that would show loss of efficiency as a re- 

 sult of three or four hours of work under 

 an unfavorable lighting system. In his work 

 directed along these lines he has succeeded in 

 getting methods of estimating effect which 

 after eighteen months of trial seem sufficiently 

 sensitive to differentiate between good and 

 bad lighting systems with regard to these 

 points. He has undertaken, therefore, to 

 determine (1) the lighting conditions that 

 give in general the highest level or scale of 

 visual efficiency; (2) the conditions that give 

 the least loss of efficiency for continued work ; 

 and (3) the conditions that cause the least 

 discomfort. This plan of work, it is scarcely 

 needful to remark, will involve a wide range 

 of experimentation. The crux of the problem 

 is, however, to secure reliable methods of esti- 

 mating effect. Having these methods, the 

 factors, whatever they may be, distribution, 

 intensity, quality, position of the light rela- 

 tive to the eye, etc., can be varied one at a 

 time and the effects be determined. From these 

 effects it should not be difficult to ascertain 

 what lighting conditions are best for the eye, 

 and what is the relative importance of the 

 factors that go to make up these conditions. 

 Further, it should be possible on the practical 

 side to test out and perfect a lighting system 

 before it is put on the market; also to deter- 

 mine the best conditions of installation for a 

 given lighting system; to investigate the effect 

 of different kinds of type and paper on the 

 eye; to study the effect of different kinds of 

 desk lighting, etc. In short, it is obvious that 



the usefulness of such tests is limited along 

 these lines only by their sensitivity. 



A detailed description of the tests we are 

 using has already appeared in print.- Time 

 can not be given to them here. A brief report 

 only of some of the results of the work in 

 which they have been employed is possible in 

 the time placed at my disposal. 



In the study of the problems presented to 

 us in this field it has been thought best to 

 conduct the investigation at first along broad 

 lines in order to determine in a general way 

 the conditions that affect the efficiency and 

 comfort of the eye. Later a more detailed 

 examination will be made of the ways in 

 which these conditions have been worked out 

 in the various types of lighting systems in use 

 at the present time. The following aspects of 

 lighting sustain an important relation to the 

 eye: the evenness of the illumination, the 

 diffuseness of light, the angle at which the, 

 light falls on the object viewed, the evenness 

 of surface brightness, intensity and quality. 

 The first four of these aspects are very closely 

 interrelated, and are apt to vary together in 

 a concrete lighting situation, although not 

 in a 1 : 1 ratio. For the purposes of this paper 

 these aspects will be grouped together and 

 referred to as the distribution of light and 

 surface brightness in the field of vision, or 

 still more generally as distribution. The ideal 

 condition with regard to distribution is to have 

 the field of vision uniformly illuminated with 

 light well diffused and no extremes of sur- 

 face brightness. When this condition is 

 attained, the illumination of the retina will 

 shade off more or less gradually from center to 

 periphery, which gradation is necessary for 

 accurate and comfortable fixation and accom- 

 modation. 



The factors we have grouped under the 

 heading distribution can be most conveni- 

 ently discussed perhaps with reference to four 

 types of lighting systems in common use 



2 ' ' Tests for tbe Efficiency of the Eye Under Dif- 

 ferent Systems of Illumination and a Preliminary 

 Study of the Causes of Discomfort, ' ' Transactions, 

 of the Illuminating Engineering Society, 1913, 

 VIII, pp. 40-60. 



