VOLTAGE AND CANDLE-POWER 519 



the rated voltage Vst, usually 110. The average exponent K is 

 found to be as follows : 



Mazda B lamps 3.6 



Mazda C2 lamps 3.8 



Mazda C lamps 4.1 



100- watt carbons 5.7 



50-watt carbons 5.9 



30-watt carbons 6.1 



20- watt carbons 7.2 



This relation, however, is not very reliable since the exponent k 

 is not constant over a very wide range of voltage. 



For the older forms of carbon lamps, the value of k is much 

 higher. Even for those here used it is higher than for the modern 

 Mazda lamps. For that reason much better regulation is required 

 for the older types of lamps than for those most commonly u^ed at 

 present. As the curves indicate the Mazda B lamp permits of more 

 variation in voltage for a certain change in candle-power than does 

 any other type of lamp tested. In other words, the change in in- 

 tensity of illumination will be less noticeable in the case of a 

 Mazda B lamp for a certain change in voltage than in the case of 

 any other type of lamp tested. 



If the voltage changes came in very quick succession (say at half 

 second intervals) the changes in illumination would make them- 

 selves felt much more for the small-sized lamps than for the big 

 ones, because the filaments are thinner and hence cool off much 

 more quickly. This, however, has no detrimental effects upon the 

 results herein given. 



Physics Laboratory, 

 Iowa State College, 



