RIDDLE— Matching Colours. S5 



racy by their aid. Colours matched by artificial illnminatlon 

 were found to be not quite accurate when daylight was brought 

 to bear on them. The response to industrial necessity has now 

 given us a source of illumination, which is wonderfully near 

 daylight. Due chiefly to intensive industrial work, stimu- 

 lated by war needs, a demand existed for an artificial source of 

 illumination which would approximate daylight in so far as its 

 radiation was concerned. This was felt especially in the tex- 

 tile industry, and wherever colour had to be matched. The 

 Research Laboratories of the largest electric lamp concern in 

 America, took up the problem, and the Mazda C-2 lamp was the 

 sequel. Certain structural modifications were made, but the 

 chief factor is the bluish glass which has been used. This was 

 selected after close research in order to provide a filtering 

 medium, such that the spectrum of the filtered radiation would 

 closely approximate the spectrum of solar radiation. For all 

 work where colour is concerned, the lamp has proved to be ideal. 

 It is an interesting experiment to take lamps representative of 

 the various milestones in the evolution of electric lighting, and 

 wire them up so as to make them immediately ready for com- 

 parison. Take the following four lamps — 



Carbon Filament Lamp. 



Vacuum type Metal Filament Lamp. 



Mazda C gas-filled Metal Filament Lamp — commonly 



called |-watt type. 

 Mazda C2 gas-filled Metal Filament Lamp — commonly 



called the "Blue Glass" or ''Daylight Lamp." 



The radiation from the Carbon Filament Lamp appears 

 fairly white when it is the only source of illumination. It in- 

 stantly assumes a reddish-yellow tinge when the vacuum lamp 

 is switched on. This lamp in turn appears yellow by com- 

 parison with the ^-watt type, which is very brilliantly white, 

 but even the -^-watt type suffers by comparison with the type 

 C2. By comparing the first and last lamps, one can hardly 

 believe that the radiation from the former ever did appear 

 white. Whilst the ordinary ^-watt type is a great advance on 

 previously existing types, and gives a radiation approximating 

 very closely to the ideal, the C2 lamp goes further, and stops 

 little .short of perfection. 



As conoerning current consumption. One can say roughly, 

 avoiding techniralities essential to accuracy, that for equal 

 candle powers, the ordinary metal filament lamp takes only one 

 fourth of the current used by the carbon filament lamp. Simi- 



