90 



SCIENCE 



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



sity; but the system never proved so favorable 

 in. this regard as even the semi-indirect system. 

 In the tests made under the direct system care 

 ■was taken to have the fixtures in the 

 same position in the room ia every case as 

 they were for the semi-indirect system. The 

 most favorable intensity is secured by an in- 

 stallation that gave 1.16 foot-candles in the 

 horizontal, .85 in the 45° position and .46 

 ia the vertical. At this intensity, however, 

 the loss in the efficiency of the eye for three 

 hours of work was almost four and one half 

 times as great as for a wide range of inten- 

 sities for either the indirect system or day- 

 Ught. 



Two facts, then, may be emphasized at this 

 point. (1) Of the lighting factors that influ- 

 ence the welfare of the eye, those we have 

 grouped under the heading distribution appar- 

 ently are fundamental. They seem to be the 

 most important we have yet to deal with in our 

 search for the conditions that give us the mini- 

 mum loss of efficiency and the maximum com- 

 fort in seeing. If, for example, the light is 

 well distributed in the field of vision and there 

 are no extremes of surface brightness, our 

 tests seem to indicate that the eye, so far 

 as the problem of lighting is concerned, is 

 when the proper distribution is present, inten- 

 sities high enough to give the maximum dis- 

 crimination of detail may be employed with- 

 out causing appreciable damage or discomfort 

 to the eye. (2) For the kind of distribution 

 effects given by the majority of lighting 

 systems in use at the present time, our results 

 show that too much light is being employed 

 for the welfare and comfort of the eye. 



The effect of quality of light on the eye has 

 been the subject of much discussion and much 

 misunderstanding. There seems to be a feel- 

 ing even among lighting engineers and oph- 

 thalmologists that colored light gives better 

 results for seeing than white light. Some, for 

 example, hold that the kerosene flame furnishes 

 the ideal source of light and that its virtues 

 are due largely to the yeUow quality of the 

 light it gives off. While the writer has not 

 as yet begun a systematic study of the effect 

 of quality of light, and while he is, therefore. 



not as yet willing to commit himself on this 

 point, he will say that when ratensity and dis- 

 tribution are equalized, an installation of clear 

 carbon lamps, which gives a light compara- 

 tively rich in yellow and red, causes the eye 

 to fall off more in efficiency as the result of 

 3-4 hours of work than an installation of 

 clear tungsten lamps, the light from which is 

 more nearly white. In short, the question 

 whether or not white or colored light is better 

 for the eye can not be answered until definite 

 tests are made of this point alone under con- 

 ditions in which all other factors are rendered 

 constant. The effects of the kerosene flame, 

 for example, as compared with other sources 

 of illumination, must be tested under a system 

 of installation that gives the same intensity 

 at the source, and, as nearly as possible, the 

 same distribution in the field of vision as is 

 given by other illuminants. This has not been 

 done at all. Our judgment of the compara- 

 tive merits of the color quality of the light 

 given by it have been based on the roughest 

 kinds of impression, obtained under condi- 

 tions of installation in which there has been 

 no attempt at control of the other factors that 

 influence the effect of light on the eye. The 

 work that has been done up to this time on the 

 relation of quality of light to seeing has been 

 confined to visual acuity as determined by the 

 momentary judgment, and even this work 

 which alone can give no safe grounds at all 

 for drawing general conclusions as to the 

 effect of light on the weKare of the eye, shows, 

 whenever the comparison has been made, that 

 white light gives a greater acuity of seeing 

 than light with a dominant color tone. If, as 

 has been maintained by some on the grounds 

 of their working experience, the kerosene flame 

 is easier on the eye than the more modem 

 sources of illumination, the writer would be 

 inclined, more especially in view of his results 

 on the effect of differences in intensity on the 

 efficiency of the eye, to ascribe the benefit, 

 whatever there may be, to the low intrinsic 

 brilliancy of the kerosene flame. For, as has 

 already been stated, it may be safely said that 

 for the kind of distribution effects we are 

 getting from the large majority of our lights 



