SCIENCE 



[N. S. Vol. XL. No. 1020 



loses practically notLiiig in efficiency as the 

 result of three to four hours of work under 

 daylight. It loses enormously for the same 

 period of work under the system of direct 

 lighting selected for our work and almost as 

 much under the system of semi-indirect 

 lighting. Under the system of indirect 

 lighting, however, the eye loses but little 

 more than it loses in daylight. The results 

 of these tests show also that acuity of vision 

 as determined by the momentary judgment is 

 higher for the same foot-candles of illumina- 

 tion for the daylight system than for the 

 systems of artificial lighting, and that for the 

 latter systems, it is highest for the indirect 

 system, next highest for the semi-indirect 

 system, and lowest for the direct. It will thus 

 be seen that for all purposes of clear seeing, 

 whether the criterion be maximum acuity or 

 the ability of the eye to hold its efficiency for 

 a period of work, the best results are given in 

 order by the systems that give the best dis- 

 tribution of light and surface brightness. The 

 effect of distribution is not so great, however, 

 on the ability of the fresh eye to see clearly as 

 it is on its power to hold its efficiency. 



The loss of efficiency found in the above 

 work seems to be predominantly, if not en- 

 tirely muscular, for the tests for the sensitiv- 

 ity of the retina show practically no loss of 

 sensitivity as the result of work under any of 

 the lighting systems employed. The following 

 reasons are suggested why the muscles of the 

 eye giving both fixation and accommodation 

 should have been subjected to a greater strain 

 by the systems of direct or semi-direct light- 

 ing, than by the system of indirect light- 

 ing or daylight. (1) The bright images 

 of the sources falling on the peripheral 

 retina which is in a perpetual state of dark- 

 ness-adaptation, as compared with the cen- 

 tral retina, and is, therefore, extremely sensi- 

 tive in its reaction to such intensive stimuli, 

 set up a reflex tendency for the eye to fixate 

 them instead of, for example, the letters which 

 the observer is required to read. (2) Like- 

 wise, a strong reflex tendency to accommodate 

 for these brilliant sources of light, all at 

 different distances from each other and the 



lettered page, is set up. (3) These brilliant 

 images falling on a part of the retina that 

 is not adapted to them, causing as they do 

 acute discomfort in a very short period of time, 

 doubtless induce spasmodic contractions of the 

 muscles which both disturb the clearness of 

 vision and greatly accentuate the fatiguing 

 of the muscles. The net result of all these 

 causes is excessive strain, which shows itself 

 in a loss of power to do work. In the illu- 

 mination of a room by daylight, however, 

 with a proper distribution of windows, the 

 situation is quite different. The field of 

 vision contains no bright sources of light to 

 disturb fixation and accommodation and to 

 cause spasmodic muscular disturbances due 

 to the action of the intensive light sources on 

 the dark-adapted and sensitive peripheral 

 retina. As has already been pointed out, the 

 light waves have suffered innumerable reflec- 

 tions and the light has become diffuse. The 

 field of vision is comparatively speaking uni- 

 formly illuminated and there are no extremes 

 of surface brightness. The illumination of 

 the retina, therefore, falls off more or less 

 gradually from center to periphery, as it should 

 to permit of fixation and accommodation for a 

 given object with a minimum amount of strain. 

 It is not our purpose, however, to contend 

 that distribution is the only factor of impor- 

 tance in the illumination of a room. We have 

 chosen to begin our work with types based on 

 distribution, only because it has seemed to us, 

 both from our own work and from a survey of 

 the work done by others, that this is the most 

 important factor with which we have yet to 

 deal in our search for the conditions that give 

 minimum loss of efficiency and maximum 

 comfort in seeing. The quality of light and 

 its intensity at the source are already pretty 

 well taken care of, apparently better taken care 

 of, at least in general practise relative to their 

 importance to the eye, than is distribution. 

 A systematic study of factors, however, can 

 not stop with an investigation of the effect of 

 distribution alone. The intensity and quality 

 of light must also be taken into account. For 

 example, one of the most persistent questions 

 asked by the illuminating engineer is, " How 



