LIGHTING IN ITS RELATION TO THE EYE. 

 By C. E. FERREE and G. RAND. 



(Read April 13, 1917.) 



1. Introduction. 



The work of which this paper is a brief outhne was done under 

 the auspices of the American Medical Association's subcommittee on 

 the hygiene of the eye, of which Dr. WilHam Cambell Posey, of 

 Philadelphia, is chairman, and has been in progress for six years. 

 The object of the work has been to compare the effect of different 

 lighting conditions on the eye, and to find the factors in a lighting 

 situation which cause the eye to lose in efificiency and to experience 

 discomfort. In all 52 different lighting situations have been investi- 

 gated, selected with special reference to the problem in hand. Also 

 a number of miscellaneous experiments have been conducted per- 

 taining to the hygienic employment of the eye. 



Confronting the pro'blem of the effect of different lighting con- 

 ditions on the eye, it is obvious that the first step towards systematic 

 work is to obtain some means of estimating effect. The prominent 

 effects of bad lighting systems are loss of efificiency, temporary and 

 progressive, and eye discomfort. Three classes of effect, however, 

 may be investigated: (i) The effect on the general level or scale of 

 efificiency of the fresh eye; (2) loss of efficiency as the result of a 

 period of work; and (3) the tendency to produce discomfort. A 

 description of tests designed especially for this work has previously 

 appeared in print. Some of these tests have been designed to de- 

 termine the eye's aggregate loss in functional power, others to aid 

 in the analysis of this effect. Time can be taken here only for the 

 briefest mention of the principles on which they are based. The 

 one with which the greater part of the work has been done is a test 

 for determining the power of the eye to sustain clear seeing. Just 

 two principles are involved in this test. One is that visual acuity 

 or clearness of seeing may be measured by the smallest visual angle 



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