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almost extinct; and when the newer forms of lamps were substituted for the older form, the term “2000-cp arc light” lost the only fixed and definite meaning that it had ever possessed.
This was the condition of affairs that recently brought about a very thorough sifting of the subject of candle-power rating with relation to contract obligations in the city of Colorado Springs. Briefly stated, the controversy arose as follows: a contract for street lighting was drawn in 1898, which called for the use of "arc lamps of standard 2000 candle-power." The oid form of open-arc lamp, which had been made to father this rating by the committee before mentioned, was used for a certain length of time without objection by the city. With the advent of the enclosed-arc lamp, however, the system was changed, and series alternating enclosed lamps were installed in the streets. These furnished the street illumination for something over a year without protest on the part of either the citizens or public officials, when, through the exigencies of politics, or from a suddenly awakened zeal on the part of certain public officials to protect the rights of the citizens (the conditions are sometimes strangely coincident), it was discovered that the lamps in use did not give 2000 candle-power, but somewhere near 300 candle-power instead, and a claim was made for a proportional rebate in the lighting bills already paid. The controversy was finally settled according to the most approved modern methods; namely, by reference to a board of arbitrators.
In the hearing of the case it is probable that the question of candle-power ir. particular, and the operation of an arc lamp in general, was more minutely threshed out by the most prominent experts in the country than ever before in the history of electric lighting. The testimony ran the whole gamut, from the frank admission of aldermen that they had not the slightest idea what candle-power meant, and cared less, to a stereopticon demonstration by a college professor of the difference between the formation of the alternating and the direct-current arcs.
Incidentally, it may be of interest to state that, at the hearing of his case, the profession of illuminating engineering was proclaimed officially for the first time; two of the expert witnesses, in qualifying, gave their profession as that of illuminating engineer. It may also be stated here that had the services of such it professional illuminating engineer been secured by either of the
parties to the controversy, if for no other purpose than to assist in drawing the contract, or to advise on the change of lamps made, the whole litigation, with its attendant expenses and annoyances, would have been avoided.
The first contention of the city was that the contract called for 2000-cp lamps, and that therefore the lamps furnished should give actually 2000 candle-power; this contention being ruthlessly swept away by the experts for both sides, who unhesitatingly stated that the term was only a popular fiction and referred, if to anything, to a particular type of lamp rather than to candlepower. Having been routed from the first line of defense, it fel! back upon the difference in candle-power between the old openarc lamp and the particular kind of enclosed-arc lamp that had been substituted. This defense proved to be impregnable, and an award was made to cover the deficiency. As the arbitrators unanimously agreed that there was no evidence of any attempt to defraud, or of bad faith on either side, the whole controversy was the result of indefinite and misleading statements in the contract.
As before stated, it was testified by some of the aldermen that that they had no idea of what the term "candle-power" meant, and were only anxious to secure the best light possible at the lowest rate. On general principles, they were fulfilling their whole duty as representatives of the citizens. Using the term "city" to signify the citizens, and not any one or more of the city officials, the city really had no particular interest in the term "candle-power.” It supposed it was buying and receiving a certain illumination of its streets, and in judging of this illumination candle-power had no place. It was simply a question of what illumination made the streets most serviceable at night.
Generally speaking, the lighting of streets has two purposes: first, to facilitate traffic; and second, to prevent the commission of crimes. In the smaller towns and cities the first is by far the more important object. So far, then, as the city is concerned the only question at issue is a very practical one, which requires no expert or technical knowledge, but judgment based upon mere "horse sense.” In judging of two different systems of street
” illumination, the question of candle-power, voltage, watts, and the rest of the strange tribe of queer-sounding names, is of no consequence whatever from the citizen's point of view. The
strange thing to be decided is, by which system of illumination is traffic in the streets most facilitated ? To be sure, the illuminating engineer knows that this judgment depends upon intensity of illumination, size of the actual or apparent source, intrinsic brilliancy, and various other technical considerations. The citizen does not know the various elements making up good illumination, but is quite as competent to judge of the actual result as the most erudite expert.
The use of the single term candle-power as a basis for lighting contracts is therefore objectionable from any point of view. To the citizen it either conveys no meaning at all or is assumed to refer to the degree and effectiveness of the illumination of the streets, which is very far from the truth. To the party furnishing the light it may refer to a certain type of lamp, or to intensity in a specified direction, or to the total flux of light, or to the lcwer hemispherical flux. The use of a term in a contract upon which payments are to be based, which even to those familiar with the technology of the subject may have any one of a halfdozen meanings, and to the layman either no meaning at all or a meaning apart from any of those understood by the engineer, is manifestly opposed to the requisite of definiteness which should be the first aim in the wording of all contracts. Beyond doubt there is no term having any pretense to scientific accuracy that is capable of so many different constructions, and is so loosely used, as this term candle-power; and until some competent authority has given it a fixed meaning, and this meaning has become reasonably familiar to those dealing with the subject, the only safe way is either to omit it altogether from the phraseology of legal documents or carefully and rigidly define the particular sense in which it is used in each case.
In view of the controversies that have arisen from the unjustified and careless use of the 2000-cp rating for arc lamps, and the self-evident need of greater accuracy in the terms used to designate the performances of light-sources, it is astonishing to find a present tendency on the part of manufacturers to still further befog the situation. Compared with the commercial rating of an incandescent electric lamp by its wattage, the designation of an arc lamp of a particular type as a 2000-cp light is definite and sane. Furthermore, the 2000-cp fiction had the excuse of having originated innocently, which is more than can be said of the watt-rating fallacy.
The advantages of smaller units for street lighting in the uniformity of illumination produced are indisputable. This fact, in connection with the equally indisputable fact that incandescent lamps of far higher efficiency than the carbon filament type are destined soon to become commercially practical, must have a wide influence in the near future on methods of electric streetlighting contracts of the near future. The designation of such lamps by their wattage alone is unfair alike to the consumer and producer, and is therefore inevitably bound to become a source of contention and dissatisfaction if persisted in. The satisfied customer is the one who receives what he pays for, judged from his point of view. The citizen buys light, not for the sake of the light itself, but for the illumination that it produces. When the aldermen in Colorado Springs directed their efforts solely to obtaining all the light that they could for the money, they were doing exactly right from their point of view; by “light” they meant illumination, and so long as they got better illumination, or, as they would have expressed it, more light, for a given sum, or at a less rate than before, they were quite satisfied to let the producing company have whatever advantages might be obtained from any improvements in the ways and means of producing illumination.
What, then, is to be substituted for this generally discredited and ambiguous term “candle-power?” In the present state of the art of illuminating engineering the answer to this question is simple; the foot-candle as a unit for measuring illumination is a strictly definite term without possibility of misconstruction or ambiguity. The single objection to the use of this term as a basis of lighting contracts heretofore has been the want of practical means of measuring illumination; but happily this condition no longer exists. There are at the present time three or four instruments for measuring illumination which compare very favorably with the most approved instruments for measuring intensity of light or candle-power. It only remains, then, to specify the direction in which the illumination is to be measured; that is, either a horizontal or vertical piane, or a plane perpendicular to the principal rays at the point measured. The measurement of illumination is
something which the layman of ordinary intelligence can quickly comprehend, and the matter therefore of determining whether or not a contract is being carried out is capable of direct verification by the citizen or official without the indirect method of referring the matter to an expert; for expert testimony in legal controversies is notoriously unsatisfactory. The expert on illumination should be used like the doctor or lawyer—to prevent trouble rather than cure it.
The lessons to be learned from the Colorado Springs controversy in regard to the drawing of lighting contracts are:
If the term "candle-power" is to be used at all, its exact meaning as used in the particular contract should be carefully defined.
Illumination, measured in foot-candles, is a more scientific, exact and generally satisfactory basis for a contract than light.
The watt consumption of a lamp should never be used as a measure of its light-giving power.
Every lighting contract should be examined and approved by a competent illuminating engineer.
THE PRESIDENT: With your approval we will defer discussion until we have heard the paper by Mr. Floy on a kindred subject.
During the preliminary arrangements for the programme, many of our members asked if it would be possible for them to visit and inspect the National Bureau of Standards while in Washington. The director of the bureau kindly replied that he would be glad to have such a visit made by our delegates. Dr. Stratton will personally make the announcement regarding the bureau at this time. I have pleasure in presenting to you Dr. S. W. Stratton, director of the National Bureau of Standards, of Washington.
DR. STRATTON: Gentlemen, I came here this morning to extend to the members of the National Electric Light Association, through its president, an invitation to visit the laboratories of the Bureau of Standards, but he has insisted that I make this announcement to you directly.
The Bureau of Standards is but a few years old, but on account of the great importance of electrical standards the section of the bureau devoted to that work was one of the first