July 17, 1914] 



SCIENCE 



87 



public lighting we can not tope to get rid of 

 eye-strain with its complex train of physical 

 and mental disturbances. 



It is not our purpose, however, at this time 

 to attempt a final rating of the merits of 

 lighting systems. For that our work is still 

 too young. Moreover, there are relatively 

 good and bad systems of each type, and good 

 and bad installations may be made of any 

 system. What we hope to do is by making an 

 appropriate selection and variation of condi- 

 tions to find out what the factors are that 

 are of importance to the eye, and from this 

 knowledge as a starting point to work towards 

 reconstruction. 



With regard to the effect of the distribu- 

 tion of light and surface lightness on 

 the eye a brief statement will be given here 

 only of its effect on efficiency; and in the 

 consideration of efficiency loss of efficiency 

 will receive the major part of our attention. 

 'Ho attempt will be made, for example, to pre- 

 sent the results of the study of the factors 

 producing discomfort. The study of these 

 factors haa constituted for us an entirely 

 separate and independent piece of work inves- 

 tigated by separate and independent methods. 



Our tests for loss of efficiency' show that 



ciple of direct lighting offers as great possibilities 

 in this direction as the indirect; still he permits 

 this also to remain an open question in his mind. 

 It is obvious that much can be accomplished for the 

 ■welfare of the eye in cases both of the direct and 

 eemi-indirect systems by using sources of large 

 area and of low intrinsic brilliancy, by removing 

 them as much as possible from the field of vision, 

 by employing better means of diffusing the light, 

 etc. 



5 The tests were made in a room 30.5 feet long, 

 22.3 feet wide, and 9 feet high. The artificial 

 lighting was accomplished by means of two rows 

 of fixtures of four fixtures each. Each tow was 6 

 feet from the side wall and the fixtures were 6 

 feet apart. The reflectors were in the different 

 cases 19-26 inches from the ceiling. Clear tungsten 

 lamps were used as source. The voltage was kept 

 constant by means of a voltmeter and a finely grad- 

 uated wall rheostat placed in series with the light- 

 ing circuit. In case of the direct system two bulbs 

 making an angle of 180° were used for each fixture 

 and the distribution was obtained by means of white 



when the intensity and quality of the light 

 are equalized at the point of work, the eye 



slightly concaved porcelain reflectors 16 inches in 

 diameter fastened directly above. In case of the in- 

 direct system corrugated mirror reflectors, enclosed 

 in brass bowls, were used. For the semi-indirect 

 system the distribution was obtained by means of 

 inverted alba reflectors 11 inches in diameter 

 which threw a part of the light against the 

 ceiling and transmitted the rest directly to 

 the room, minus a rather large absorption quan- 

 tity. The daylight illumination came from 

 three windows all on one side of the room and 

 situated in a line parallel with the line of 

 sight used when making the tests. These windows 

 were so sheltered that it was never possible for 

 them to receive light directly from the sun or 

 from a brightly illuminated sky. Moreover, the 

 light from one of them, the one nearest the ob- 

 server, was further diffused by passing through 

 a diffusion sash made of double thick glass ground 

 on one side. The intensity in foot-candles was 

 made equal at the point of work for all the sys- 

 tems employed. In making this equalization the 

 light was photometered in five directions at the 

 point of work: with the receiving surface of the 

 photometer in the horizontal plane, at angles of 

 45° and 90° pointing towards the observer, and at 

 angles of 45° and 90° pointing in the opposite di- 

 rection. In installing the lights in the different 

 systems it was impossible to make the intensity 

 equal in all of these directions. Oare was taken to 

 make it equal in the plane of the test card, i. e., 

 the vertical plane, ajid as nearly as possible equal 

 in the other planes. The Sharpe-Millar portable 

 photometer was used to make these measurements, 

 also another method mentioned in a former paper 

 (op. cit., p. 49) which is more sensitive to day- 

 light illumination than is the Sharpe-Millar 

 method. The effect of varying distribution of 

 light was thus tested under conditions in which 

 quality and intensity were reduced as nearly to a 

 constant as was possible with the systems em- 

 ployed. The intensity in the vertical plane was 

 Blade in each case 1.4 foot-candles or approximately 

 so. Space can not be taken here for an engineer- 

 ing specification of the Installations used and the 

 lighting effects produced. A full report of the 

 work including detailed brightness and illumina- 

 tion measurements, photographs showing the il- 

 lumination effects obtained, descriptions of installa- 

 tions, etc., will be published in the Transactions of 

 the Illuminating Engineering Society. 



