[Electric engineering.] . percandlepower is, therefore, a fair average. 34. Connections for Testing.—When testing lamps, acareful record should be kept of the length of time they haveburned, also of the voltage and current. With this data athand, together, of course, with the readings of candlepoweras given by the photometer, the efficiency of the lamp at any § 16 ELECTRIC LIGHTING. 27 time during the test may be at once determined. Accurateinstruments must be used, and their scales should be sodivided that the ammeter or mil-ammeter may be read toyoVo ampere and the voltmeter to TV volt. A va
[Electric engineering.] . percandlepower is, therefore, a fair average. 34. Connections for Testing.—When testing lamps, acareful record should be kept of the length of time they haveburned, also of the voltage and current. With this data athand, together, of course, with the readings of candlepoweras given by the photometer, the efficiency of the lamp at any § 16 ELECTRIC LIGHTING. 27 time during the test may be at once determined. Accurateinstruments must be used, and their scales should be sodivided that the ammeter or mil-ammeter may be read toyoVo ampere and the voltmeter to TV volt. A variable resist-ance should also be inserted in series with the lamp so thatthe voltage across the lamp terminals may be kept nearlyconstant. Fig-. 18 shows the general scheme of connections. Theammeter A is connected in series with the lamp and the volt-meter [across its terminals. Readings oiA are taken withthe voltmeter cut out, so that A does not measure the cur-rent through the voltmeter as well as that through the. or^forage Bafferi/. Fig. 18. lamp. A. good ammeter and voltmeter are to be preferred toa wattmeter for this kind of work, as the results are morelikely to be accurate. Continuous current should, if possible,be used for all testing, as alternating-current instrumentsare more likely to lead to inaccurate results. Current sup-plied from a continuous-current dynamo running at constantspeed may be used, but it will be found more satisfactory touse current from a storage battery if it can be obtained, asthe latter current is perfectly steady. Readings of candle-power, current, and voltage should be taken as nearly simul-taneously as possible. 28 ELECTRIC LIGHTING. §16 35. Lamp Estimates.—With an average power con-sumption of watts per candlepower, a 16-candlepowerlamp would require 16 X = watts. The currentthat the lamp will require will depend on the voltage atwhich it is operated. The current in any case can beobtained by the following formula or r
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