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diagram, Fig 19, this is taken as the standard and is represented by the 100 per cent line. In much of the most expert color matching work the light of the north sky is employed as being the most constant form of daylight. Ives has arrived at a determination of the quality of north sky light which is represented on the diagram as Curve B. For various purposes north sky light, sun

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A-"Black body" at 5000 degrees absolute (equivalent to noon sunlight)
B--Blue sky (Ives) I.E.S. Transactions, 1910, page 208

page 952

220

C--Daylight glass with Mazda C lamp (Brady) I.E.S. Transactions, 1914,
D-Bluish glass with Mazda C lamp (Sharp) I.E.S. Transactions, 1915, page

E-Blue bulb Mazda C lamp

F-Mazda B lamp (7.9 lumens per watt)

G Mazda C lamp (20 lumens per watt)

H-Moore tube (Moore) Transactions I.E.S. 1916, page 192

I-Trutint glass (Luckiesh) I.E.S. Transactions, 1914

J-Trutint glass (Luckiesh) I.E.S. Transactions, 1914

the light from mazda lamps may be most suitable. In g an artificial daylight equipment it should be decided first ality of light is desired. Almost any desired quality withrange named can be supplied. Generally speaking, in proin as the color departs from that of mazda light toward at the north sky light, the artificial daylight equipment is used becomes less and less efficient as a light producer. Leventieiess, for certain purposes, the most inefficient of artificial equipments may be the most effective.

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In addition to daylight Curves A and B on the diagram, e F shows the distribution of light throughout the visible cum from mazda lamps and Curve B shows the correspond

stration of light from mazda gas filled lamps. All other es represent the distribution of light throughout the visible.

from lighting equipments which are designed to produce x matins of various qualities of natural light. Thus one a tam a close approximation of blue sky light or of noon

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tor of afternoon light, depending upon his requirements. For certain purposes it is possible that an approach toward ht as represented by the equipment producing Curve E or D) may serve all requirements in that they provide a light re nearly white than that of either the mazda vacuum raz la gas filled lamps, one which lies between these illua 1 daylight and helps to bridge the gap between the ir certain other purposes a better approximation of sun⚫are; resented by Curve Cor J may be required Again ser approximation of north sky light as represented by If and I may be necessary. It is conceivable that the

nall deviations of Curves C and J from sky light may dffculty in some very exacting uses to which these dachght equipments may be put Thus it is most imat the actual requirements be determined before the daylight equipment is sought

• is believed that the hell for artificial daylight equipments tartant one and that in cultivating it member companies - 1 new employment for h♫ ting and at the same time may useful service in promoting certain forms of in lustry -A beret fore have suffered from the lack of such daylight

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BUREAU OF STANDARDS

Members are perhaps generally familiar with Circular 55, issued by the Bureau of Standards, Department of Commerce, about a year ago. This circular, which is most interesting and instructive, and which has had a wide circulation, is designed, as the Department announces in the introduction

"(1) to give information as to units, methods, and instruments of measurement useful in household activities, (2) to describe available means of assuring correct quantity in articles bought by weight and measure, and (3) to give other facts of interest which would awaken an appreciation of the role of measurement in daily life."

So far as the circular refers to electric lamps and electric lighting your Committee has been in communication with the Bureau and has submitted suggested changes that will bring the information and data up to date. It is believed that these suggestions will be favorably considered by the Bureau in connection with a revised edition of this circular which is now in preparation.

The Department also has in preparation a circular covering "Standards for Electric Service." This presentation, which will be known as Circular 56, is to be somewhat similar in treatment. to Circular 32 now in its third edition and covering "Standards. for Gas Service."

A sub-committee of the Association has been studying this important proposed publication and your Lamp Committee has been in close touch with this committee respecting the chapters and items which have to do with incandescent lamps and related subjects.

Standard Specifications for Incandescent Lamps

A revision of the "Standard Specifications for Incandescent Lamps" has been effected during the past winter. The new specifications appear in Circular No. 13 of the Bureau of Standards bearing the date of October 23, 1915, and are also issued by the lamp manufacturers in slightly different form.

principal differences between the new edition of the ats and the edition previously in force are that all a sum lamps of sizes larger than 100 watts are elimi

the schedules and 10 watt mazda vacuum lamps in have been added. The limits of acceptability in watts atts per candle for mazda vacuum lamps have been nar aterially, imposing a requirement for closer rating The

ng values of ethciency ratings have been increased set to acron me date the specifications to the actual inses in eff,,encies of lamps which have been effected during

two years Acceptability limits for carbon and gen ave been widened in view of the lessening demand for ex and in most cases these types of lamps are no longer in general features the new edition of the specifications the preceding edition

PROPOSAL TO RATE LAMPS IN LUMENS INSTEAD OF

CANDLEPOWER*

The traditional basis of rating incandescent lamps is the mean horizontal candlepower. Successive experiences with carbon filament lamps, tantalum lamps and gas-filled tungsten lamps have shown this measure to be an inaccurate and inadequate index to the total illuminating power of a lamp. Such inaccuracy in the past has led to confusion and improper practice. During the past year or two this has become so pronounced in connection with gas-filled lamps that the mean horizontal candlepower has practically been abandoned as a basis of rating. As a substitute for the mean horizontal candlepower the mean spherical candlepower might be employed as it is free from most of the objections which can be urged against the mean horizontal candlepower. A preferable unit, however, is the lumen which is the unit of light flux. Roughly, the lumens of a tungsten vacuum lamp are about ten times the mean horizontal candlepower. More. accurately, the lumens are 12.57 times the mean spherical candlepower of a lamp. (12.57 will be recognized as the ratio between the area of a sphere and the square of its radius, i.e. 4′′). The lumen is a logical unit of light flux which is approved by scientific and engineering societies and by the best engineering opinion. It has the advantage that it is applicable in common to the light produced by a lamp and to the light delivered upon a plane which is illuminated. It forms the basis of a complete system which is now adopted generally in illuminating engineering practice.

It has been the practice to indicate the efficiency of incandescent lamps by a statement of the watts per candle. It has been very definitely recognized that this expression is the reciprocal of the efficiency and is nothing more than a statement of the specific consumption of a lamp. Nevertheless it has been referred to loosely as the "efficiency." When lamps are rated in lumens a natural and proper expression of the efficiency is the lumens per watt. When the efficiency of lamps is increased the lumens per watt properly are increased. This straightening out * Illuminating Engineering Society-Report of Committee on Nomenclature and Standards, Transactions, 1915, page 647.

American Institute of Electrical Engineers-Standardization Rules, Section 351.

National Electric Light Association-1915 Report of Committee on Terminology, also in 1916 report.

Bureau of Standards-Circular No. 13 (1915)-page 7.

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