86 



SCIENCE 



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



to-day: illumination, by daylight, direct light- 

 ing' systems, indirect lighting systems and 

 semi-direct systems. In the proper illumina- 

 tion of a room by daylight, we have been able 

 thus far to get the best conditions of distribu- 

 tion. Before it reaches our -windows or sky- 

 lights daylight has been rendered widely dif- 

 fuse by innumerable reflections; and the 

 windows and skylights themselves, acting as 

 sources, have a broad area and low intrinsic 

 brilliancy, all of which features contribute 

 towards giving the ideal condition of distri- 

 bution stated above, namely, that the field of 

 vision shall be uniformly illuminated with 

 light well diffused and that there shall be no 

 extremes of surface brightness. Of the sys- 

 tems of artificial lighting the best distribu- 

 tion effects, speaking in general terms, are 

 given by the indirect systems. In this type of 

 System the source is concealed from the eye 

 and the light is thrown against the ceiling or 

 some other diffusely reflecting surface, in such 

 a way that it suffers one or more reflections 

 before it reaches the eye. In some of the 

 respects most important to the eye, this system 

 gives the best approximation of the distri- 

 bution effects characteristic of daylight of 

 any that has yet been devised. The direct 

 lighting systems are designed to send the 

 light directly to the plane of work. There is 

 in general in the use of these systems a 

 tendency to concentrate the light on the work- 

 ing plane or object viewed rather than to dif- 

 fuse it, and, therefore, a tendency to emphasize 

 brightness extremes rather than to level them 

 down. Too often, too, the eye is not properly 

 shielded from the light source and frequently 

 no attempt at all is made to do this. The semi- 

 indirect systems are intended to represent a 

 compromise between the direct and indirect 

 systems. A part of the light is transmitted 

 directly to the eye through the translucent 

 reflector placed beneath the source of light, and 

 a part is reflected to the ceiling. Thus, de- 

 pending upon the density of the reflector, this 

 type of system may vary between the totally 

 direct and the totally indirect as extremes and 

 share in the relative merits and demerits of 

 each in proportion to its place in the scale. 



By giving better distribution this type of 

 system is supposed also to be a concession to 

 the welfare of the eye, but our tests show that 

 the concession, at least for the type of 

 reflector we have used,^ is not so great as it is 

 supposed to be. In fact, installed at the inten- 

 sity of illumination ordinarily used or at an 

 intensity great enough for all kinds of work, 

 little advantage is gained for the eye in this 

 type of lighting with reflectors of low or 

 medium densities; for with these intensities 

 of light and densities of reflector, the bright- 

 ness of the source has not been sufficiently 

 reduced to give much relief to the suffering 

 eye.* Until this is done in home, office and 



3 The reflectors we used were supplied to us by a 

 prominent lighting corporation, interested neither 

 in the manufacture nor the sale of lighting fixtures, 

 in response to a request for a representative semi- 

 indirect lighting system. Obviously, however, final 

 conclusions should be reserved until the tests are 

 extended to other types of reflectors. 



* The semi-indirect system used by us was but 

 little better for the eye than the direct sys- 

 tem. The direct system we employed was the one in 

 general use throughout the building in which our 

 tests were made. It was installed about six years 

 ago and is, therefore, not of the most modem 

 type. It seems to the writer safe to say, however, 

 that it gives effects fully as good as most direct 

 lighting in actual use in the country to-day. Fur- 

 thermore, it is difficult to believe that any great 

 injustice has been done to direct lighting, so far as 

 this principle of lighting has been commercialized 

 up to this time, by the selection of this system, be- 

 cause of the fact that very little less loss of effi- 

 ciency was obtained from the semi-indirect lighting 

 system, which on accoimt of its similarity to indi- 

 rect lighting represents, we have good reason to be- 

 lieve from our results, a greater modification of di- 

 rect lighting for the welfare of the eye than any 

 that is found within the class of direct systems. 

 However, a final conclusion will be reserved until a 

 more extensive investigation of the direct systems 

 has been made. The writer further does not wish 

 to be understood as contending that direct lighting 

 can not be accomplished in a way that is not ex- 

 cessively damaging to the eye. Doubtless great im- 

 provement can be made in this type of lighting if 

 proper attention is given to the fundamental prin- 

 ciples governing the effect of light on the eye. It 

 does not seem to the writer, however, that the prin- 



