High Temperatures by the Method of Colour Identity. 61 



optical methods and assumptions are admittedly open to 

 doubt. 



It is of interest now to see what are the temperatures of 

 filaments in gas-filled lamps determined by the colour-identity 

 method of measurement*. 



In estimating the temperature of the filament in a lamp 

 bulb containing gas, it must be remembered that the relation 

 between lumens/watt and temperature cannot be the same as 

 in the ordinary vacuum lamp because of the considerable 

 number of watts carried away from the filament by convection 



Fig. 6. — Gas-filled Lamps. 



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02 0'4 06 08 10 12 1'4 1/6 18 20 22 2'4 26 2 8 3t) 

 Waits per Mean Spherical Candle (Gas-filled Lamps) 



Curves showing for various gas-filled tungsten filament lamps A to E 

 the relation between the actual watts per mean spherical candle and 

 the watts per mean spherical candle of a vacuum lamp filament at 

 the same temperature. 



in the gas. Farther, the proportion of watts convected 

 depends considerably on the diameter of the wire and on the 

 density of the gas in the bulb. 



Six gas-filled lamps have been compared against an 

 ordinary vacuum tungsten lamp in order to determine the 

 difference of efficiency expressed in watts per mean spherical 

 candle or lumens per watt between the two types of lamps when 

 the colour of their radiations is identical, and therefore when 

 to a close approximation their temperatures are the same. 



* See Langmuir, Proc. Amer. Inst, of Elect. Eng. vol. xxxii. p. 1895. 



