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Photometry

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-440

2025-12-16

292

is the process of measuring the relative intensities of light. The instruments used for the purpose are called photometers. The practical working standard of intensity is the incandescent lamp. This is first standardized in terms of candle power based upon the light given by a sperm candle, and after being "seasoned" by use gives a nearly constant candle power. From tests made at the Bureau of Standards at Washington the average candle power of carbon filament lamps with a current of 0.5924 ampere was 16. The 25-watt tungsten lamp gives 20 candle power and the Welsbach mantle lamp under good gas pressure, 50 candle power or more.