Bulletin of the Bureau of Standards, Vol. 5, 555-558 (1909) Scientific Paper 115 (S115)
The authors refer to the use of tungsten filaments in "comparison lamps" such as are employed in series of tests at the Bureau of Standards. A lamp employed in this capacity is run continuously for long periods of time, and it is desirable that the change in candle-power during this time should be as small as possible. The tungsten lamp, when running at about 3 watts per c.p., yields light which matches that of a carbon lamp in colour; when burnt under these conditions lamps were found to yield very satisfactory results as regards constancy and longevity. An additional advantage is that the colour of the light can, if required, be varied within wide limits by altering the voltage. The authors then proceed to exp
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