Measures for Progress: A History of the National Bureau of Standards

STANDARDS FOR PUBLiC UTILITIES 111
Very much aware of the weights and measures investigation of the
Bureau and its assistance in setting up inspection systems in cities and States,
the new public service commissions turned to the Bureau for help. The
ensuing research that began with the measurement of lamp light was even-
tually extended to almost every aspect of public utility service.
One difficulty in establishing a uniform standard of light hinged on
the use of the term "candlepower," based by tradition on a natural light
source, the light value of an open flame measured by comparison with a
sperm oil candle. By reason of the varying sizes and designs of the sperm
candles used, the values originally derived from them differed considerably.
Thus the "candles" of the electric lamp and illuminating gas industries bore
little relation to one another, and even within the same industry the Bureau
found the "candle" had little constancy.15
As working standards, some gas and electric companies referred to
the English parliamentary candle. Most electric lamp manufacturers, how-
ever, had turned to the standard of light maintained by the Reichsanstalt,
the Hefner amylacetate lamp, for their "candle" value. The flaws that
Rosa's group found in the Hefner standard shortly after the establishment
of the Bureau led him to propose as a new standard for the electric lamp
industry the mean value of a number of 16-candlepower commercial lamps,
and to make this applicable to gas light as well as to electric light.'6
When the value of this new standard "candle" proved to be only
slightly greater than the unit maintained by the national laboratories of
England and France, the Bureau proposed an adjustment of its own value
looking to an international candle. The proposal was accepted, and in
1909 the new value, based on a simple relationship between the British
Hefner unit, the French bougie décimale, and the carbon-filament unit
maintained in Washington, became the standard for all photometric measure-
ments in this country.'7 -
Interestingly enough, a year earlier, in 1908, Waidner and Burgess
in the heat division of the Bureau attempted to construct an absolute standard
NBS Annual Report 1909, p. 7.
"See letter, SWS to Edison Lamp Works of General Electric, Harrison, N.J., Apr. 30,
1904, and attached correspondence (NSB Box 8, IEL).
In July 1904 an instructor at Cornell, Eugene C. Crittenden, was brought to the Bureau
to investigate flame standards in photometry. He remained for more than 50 years.
Under his guidance the problems of a light standard were finally resolved by the inter-
national acceptance of a "new candle" in 1948, based on two accomplishments of the
Bureau, the platinum black body standard of Wensel, Roeser, Barbrow, and Caidwell,
and the determination of spectral luminosity factors by Gibson and Tyndall. See ch.
V, p. 245, and ch. VI, p. 337.
17 NBS C15, "The international unit of light" (1909; 3d ed., 1911). The Reichsanstalt's
Hefner unit was assigned the value of 0.90 international candle.