THE LIGHTING OF INTERIORS. 



By Prof. H. Bohle, M.I.E.E. 



The advent of the metal filament lamp has greatly altered the 

 methods for lig-hting the interiors of buildings. The high candle 

 power incandescent lamp is rapidly driving out the arc lamp, since 

 lighting with the former is cheaper and more convenient than 

 with the latter. Cheaper if we take re-carboning and attention 

 into account, and more convenient since the glow lamp largely 

 looks after itself. 



F'or interiors flame arcs are not yet a complete success. The 

 fumes given off by these lamps are objectionable, and the light 

 is far too concentrated. Moreover, if one takes into account the 

 troubles which are connected with these arc lamps, and the 

 amount of attention they require, it will be found that, even for 

 street lighting, the saving when using flame arcs, compared with 

 metal filament lamps of the Tungsten type, is not very great. 

 The polar curves, which are very often submitted by the makers 

 of these lamps, frequently give higher candle powers than the 

 values determined by impartial tests. I do not think that the arc 

 lamp will, in future, be very much employed except for large 

 squares and very broad streets. 



As regards Interior Lighting, let us first consider the amount 

 of light required (i) for direct lighting, and (2) for Indirect 

 Lighting. 



DIRECT LIGHTING. 



In order to determine the quantity of light for difterent locali- 

 ties, I carried out a number of experiments in reading the ordinary 

 type of text-book print in rooms of different colours. The values, 

 given in Table I., are actually the mean values of a number of 

 observations by different observers. 



Table I. 



ILLUMINATION REQUIRED FOR READING IN ROOMS OF DIFFERENT 



COLOURS. 



Colour. Illumination in Candle metres (British Candles). 



Black room ... ... ... ... ... 35 



Deep red ... ... ... ... ■•■ 32 



Dark green ... ... ... ... ... 30 



Pale blue 28 



Light yellow . . ... ... ... 25 



Cream silvery ... ... ... ... 23 



White ... ... ... 20 



White (indirect light) ... 15 



