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The introduction and development of various means of lighting in recent years have been accompanied by critical comparisons between different sources of light, but none have been subjected to more careful tests than electric and gas lights, and it is due to the keen competition between these two systems that each has been brought to the state of perfection in which it is seen to-day.

It is a fully recognized fact that for units of light giving below about 100 candle-power the electric light produced with steam under normal conditions comes out more expensive than gas lighting, at any rate when comparing the cost per candlepower-hour. One can not, however, maintain that this comparison is correct and the only one of importance, in view of the present enormous development of electric lighting with small units.

In spite of all improvements that have been made in gas lighting, it has been impossible to obtain for it the peculiarities for which electric lighting is characteristic, which are commonly known to be the following: easy control of lights from a distance, agreeable shade, great adaptability, its coolness, the absence of gases caused by combustion, the beautiful and varying effects, the possibility of splitting the light into small units, the better light obtained by fixing lamps at an angle, and the possibility of using the current in a lighting installation for other purposes (heating, motors, ventilators, and so forth). Advantages of this

, kind can not be expressed in figures. They are, however, in many cases of such importance that the electric system of lighting is adopted in preference to any other, in spite of the higher cost per candle-power-hour.


Owing to the above peculiarities of electric lighting, it is very often regarded as a luxury, with the result that electric lights

* I have to thank Dr. Norden for the assistance he has given me in compiling these notes.

are burned as little as possible in order to keep the lighting bill low. Economy in this direction is easily obtained, because it is so very convenient to switch the electric current on and off again. The effect this has on the plant in the central station is, however, less desirable, since the total capacity installed is annually used for a comparatively short period. A better station load would be obtained under these conditions if more long-period consumers were tempted to buy current at more favorable terms than those offered in the uniform rate of charges. . The natural consequence of the low consumption in comparison with the capacity of the plant was a high price for current, which formed a hindrance to the introduction of electric lighting.

It has become usual to divide the annual cost for the generation of current into constant expenses and variable expenses. On this basis the constant expenses with modern steam-driven central stations of an average size are between 80 and 120 marks per kilowatt.

The variable expenses are between 2.5 and 5 pfennigs per kilowatt-hour. The figures will of course vary according to local conditions. Assuming an average of 100 marks and 4 pfennigs respectively, we get the following generating costs for the current in relation to time:

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It is evident from the above figures that the extra cost per kilowatt-hour incurred through an increase in consumption, the capacity of the plant remaining the same, is very slight indeed. This, however, is quite contradictory to the tendency for consumers to reduce their expenses for lighting by burning lamps as little as possible, because, so far as the generating station is concerned, the extra hours of consumption make very little difference in generating expenses.

If electricity works had come in before gas works, they would no doubt have had the advantage of supplying current for lighting installations which are used for long periods, as, for instance, street lighting, and so forth. The result would have been low tariffs and probably a very large development of the supply to installations burning small units of light. It would then have been exceedingly difficult for gas lighting to compete successfully with electric lighting.

In consideration of the above contradictory circumstances, central stations have charged special rates to long-period consumers by introducing tariffs with a certain fixed rate of charges calculated on the maximum current consumed and an additional price per kilowatt-hour shown on the meter. Tariffs of this kind are largely used at the present momerit, and they fairly well correspond to the actual generating costs. A general introduction is, however, impossible, owing to the great divergency in the use of current and the difficulty of bringing the influence of various classes of consumers to bear satisfactorily on the maximum capacity of the central station. Installations in private houses, for instance, always require a high local maximum, although the effect on the central station is comparatively small, because local peaks do not overlap. To charge a consumer the same fixed rate for a lamp that does not burn often as for another lamp that is lighted regularly, is no doubt a hindrance to the introduction of electric lighting. A double tariff, as extensively applied in Germany, overcomes this difficulty. The principle on which this tariff is based is to charge the normal price for current during the time of greatest consumption, but at other times to charge a very much lower price. One of the advantages of a tariff of this kind is that a power load and a lighting load will not overlap to the same extent as is the case with the single tariff or the maximum tariff.

We will now consider the influence of pressure on electric lighting. The cost of a continuous-current network is known to form a considerable item in the total capital outlay. For the last ten years preference has been given to a circuit pressure of 2 X 220 volts in Europe, contrary to American practice. The consideration that led to the introduction of this pressure is that a loss of 10 to 12 per cent in the economy.of high-tension carbonfilament lamps is more than balanced by a saving in interest and depreciation in the network. In other words, one could supply current to consumers at lower prices in compensation for lamps with a lower efficiency.

The experience gained with the length of life of 220-volt lamps is favorable. This is probably partly due to smaller fluctuations in pressure in 220-volt circuits than in those for 110

volts. A reasonable tariff and low initial expenditure with the accompanying low rates of charges led to a general introduction of electric lighting with glow lamps and helped to overcome the keen competition of gas lighting.

This is a remarkable fact, especially in Germany, where the average consumer very carefully calculates his expenses for lighting. The price of the electric light is, however, still higher than the price for gas lights, and if certain improvements in the manufacture of glow lamps had not been made just in time, the development of gas lighting and the introduction of inverted gas burners, with the accompanying higher efficiency representing an improvement of 30 per cent, might have seriously hampered the introduction of the carbon-filament lamp, although it would never have brought it to a complete standstill.

Incandescent Lamps

The improvements referred to consist of the manufacture of lamps with a high efficiency, such as Nernst lamps and metalfilament lamps.

The Nernst lamp reduces the consumption per candle-powerhour to half the value for carbon lamps, and has the advantage of being very suitable for high pressure (220 volts), which led to an extensive use of three-wire installations with 2 X 220 volts. These lamps require a certain time for lighting up after being switched on, but this is a disadvantage that very often is of no consideration. The life of Nernst lamps is practically as long as that of carbon-filament lamps, at any rate as far as continuous-current circuits are concerned. The results in alternating-current circuits are not quite as favorable.

The metal-filament lamps mentioned above consume just about one-third of the current taken by ordinary lamps with carbon filaments. One of the first of these lamps brought out in recent years is Auer's osmium lamp, with a specific consumption of 1.5 watts per candle-power. This lamp can, however, be made only for about 55 volts. Another lamp of this kind is Siemens and Halske's tantal lamp, which will burn in 110-volt circuits and takes about 1.7 watts.

The most prominent and latest of all nietal-filament lamps is the tungsten lamp. The filament made by one group of manufacturers is obtained by chemical reaction and not by com

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