LIGHTING OF INTERIORS. 317 



This table holds for distributed light, the maximum illumina- 

 tion of which is not more than 40 per cent, greater than the mean. 

 It should further be mentioned that the table has been plotted with 

 regard to equal comfort in all cases. This implies, however, that 

 the eye should roam as little as possible from the print, in the 

 rooms of the darker colours, otherwise it becomes more tired with 

 the higher illumination than with the lower one. In the latter case 

 contrast is almost entirely avoided, and it is to this that the eye 

 objects. 



The divergency in the above table may be explained as follows : 



In the darker room, on looking at the print, the aperture of the 

 pupil becomes set to a certain width as long as one does not move 

 the eye away from the book. At the same time one has the feeling 

 of surrounding blackness, and the great contrasts prevailing make 

 the eye roam instinctively. As soon, however, as the eye encoun- 

 ters the darkness the pupil extends. In the next instant the eye 

 again strikes the brilliantly illuminated paper, and consequently 

 the pupil contracts, and probably more than is necessary, because 

 it experiences a glare. But too much contraction makes the illu- 

 mination appear insufficient, and the pupil expands again. This 

 repeated expansion and contraction seem to make a higher 

 illumination necessary. 



The table shows us that the least illumination is required when 

 the illumination is approximately uniform, as obtained from in- 

 verted lamps. In reversing the lights of a lecture room, so as to 

 obtain indirect illumination by reflecting the light from the ceiling, 

 the actual illumination was reduced from 23 to 12 (average) candle 

 metres. Yet, the students were highly delighted with the new 

 arrangement and preferred it to the former method. For drawing 

 and writing purposes it was certainly preferable, because shadows 

 were almost completely avoided, a thing which cannot be prevented 

 with direct lighting, no matter how well the lamps are distributed. 

 Pronounced shadows are, however, very irritating, especially if 

 they fall in the wrong place. It will also be found that the values 

 of the above table become insufficient if the light is badly distri- 

 buted, an increase of 10 or 12 per cent, being necessary when the 

 maximum value is double the mean value. 



There is no doubt that the eye is far more dependent upon 

 contrasts than upon actual values. A lamp which will cause glare 

 at night will often not do so during the day, and if one walks 

 from the sunshine into a brilliantly artificially lighted room, the 

 latter nevertheless appears very dark. Contrasts in artificial light- 

 ing are easily avoided if we paint the room white or with light 

 yellow colours. Not only do we require less illumination in rooms 

 of light colours, but less light will give a better illumination on 

 account of the reflection of light from the walls and ceiling. 



The quantity of the reflected light depends largely upon (a) 



