LIGHTING OF INTERIORS^ 



321 



With the aid of the results so far obtained we can now find 

 the percentage increase in the illumination for rooms of other 

 colours, as long as we know the co-efficients of diffuse reflection 

 for these colours. We then get Fig. 10. If we assume the same 

 room as before and the same lamps, Fig. 10 is for lamps with 

 shades on and Fig. 1 1 with shades oft. 



iSO 



/40 



!20 



too 



PER CEMT INCOEASS IN /LLUMfhlATlOhl 



WHITE 



FAINT mv CrtB AM 



CffEAM SiLVeQV 

 LIGHT VELLOV/ 



LIGHT STQAWdERHY 

 PINK 



PALE WHITE BLUe 



LI CUT CRIEN 



DARK CREEH 



DEIEP VmOlfi/ CQAY 

 ^EDSATiN(MEDf!) 



fULL CREEN 

 & DARK RED 



o /oo 20C 300 CENT/METRES 



DISTANCE OF LAMP ABOVE TESTING PLANE. 



Fig. 10. 



Fig. 1 1 has been plotted for four colours only, as one would 

 hardly use lamps without shades in rooms with dark colours. The 

 co-efficients of diffuse reflection have been inserted in the figures.* 

 In checking the results in two actual rooms with similar wall- 

 papers, for which Bell determined the co-efficients, a good agree- 

 ment was found to exist. The furniture, however, was completely 

 cleared out. The value depends also on the size of the room. 



With the results obtained we are now able to predetermine for 

 any given room and colour the candle power necessary, giving 

 results of Table I. as average values. The candle power per 

 square metre surface (mean hemispherical) for lights with conical 

 opaque shades, has been plotted as functions of the height of the 

 lamps above the testing plane. The average value depends com- 

 paratively little on the distribution of the lamps, but the uni- 

 formity is greatly affected thereby. The effect that with great 

 uniformity less light is required, has been neglected in Fig. 12. 



• See Dr. Louis Bell, Illuminating Engineer. March, 1908. 



