STANDARDIZATION RULES OF THE A.I.E.E. 



motor windings and in the core. The mean service conditions may be 

 expressed in terms of the current which would produce the same losses 

 in the motor windings and the voltage which, with that current, would 

 produce the same core losses as the average in service. The continuous 

 capacity of the motor is given in terms of the amperes which it will 

 when run on a testing stand with covers on or off, as specified at dif- 

 ferent voltages, say, 40, 60, 80 and 100 per cent of the rated voltage 

 with a temperature rise not exceeding 90 deg. cent at the commutator and 

 75deg. cent at any other part, provided the resistance of no electric circuit 

 in the motor increases more than 40 per cent. A comparison of the equiva- 

 lent service conditions with the continuous capacity of the motor will de- 

 termine whether the service requirements are within the safe capacity of 

 the motor. 



340 This method affords a ready means of determining whether a specified 

 service is within the capacity of a given motor and it is also a convenient 

 approximate method for comparing the service capacities of different 

 mot 



APPENDIX C. PHOTOMETRY AND LAMPS. 



341 CANDLE-POWER. The luminous intensity of sources of light is expressed 

 in candle-power. The unit of candle-power is the international candle 

 maintained by the Bureau of Standards at Washington, D. C. The 

 Hefner unit is 0.90 of the international candle. 



342 LUMEN. The total flux of light from a source is equal to its mean spherical 

 intensity multiplied by 4 7T. The unit of flux is called the lumen. A 



lumen is the th part of the total flux of light emitted by a source 



having a mean spherical intensity of one candle-power. 



344 ILLUMINATION. The fundamental physical unit of illumination is the 

 centimeter-candle, or lumen per square centimeter of incident surface. 

 This is a very intense illumination. It is, therefore, convenient to express 

 illumination practically in thousandths of the fundamental unit; i.r.. in 

 millilumens per sq. cm. In English-speaking countries, the unit of il- 

 lumination commonly employed is the foot-candle or lumen per square 

 foot. A foot-candle is nearly the same illumination as a millilumen per 

 sq. cm. and is actually the more intense in the ratio 1.0764; so that n foot- 

 candles =1.0764 Xn millilumens per sq. cm. A meter candle or lumen per 

 square meter, is called a " lux ". A foot-candle is 10.764 lux, and a milli- 

 lumen per sq. cm. is exactly 10 lux. 



346 The EFFICIENCY OF ELECTRIC LAMPS is properly stated in terms of 

 lumens per watt at lamp terminals. This use of the term efficiency is to 

 be considered as special, and not to be confused with the generally ac- 

 cepted definition of efficiency in Sec. 84. 



347 a. EFFICIENCY, AUXILIARY DEVICES. In illuminants requiring auxiliary 

 power-consuming devices outside of the luminous body, such as steadying 

 resistances in constant potential arc lamps, a distinction should be made 

 between the net efficiency and the gross efficiency of the lamp. This 

 distinction should always be stated. The gross efficiency should include 

 the power consumed in the auxiliary resistance, etc. The net efficiency 

 should, however, include the power consumed in the controlling mech- 

 anism of the lamp itself. Comparison between such sources of light 

 should be made on the basis of gross efficiency, since the power con- 

 sumed in the auxiliary device is essential to the operation. 



348 A STANDARD CIRCUIT VOLTAGE of 110 volts, or a multiple thereof may 

 be assumed, except where expressly stated otherwise. 



349 WATTS PER CANDLE. The specific consumption of an electric lamp is 

 its watt consumption per mean spherical candle-power. " Watts per 

 candle " is the term used commercially in connection with incandescent 

 lamps, and .lenotes. watts per mean horizontal candle-power. 



