Abstract

The fluctuations in temperature of an ac-heated filament modulate the radiant energy produced. This paper considers the amplitude of the modulation as a function of temperature and wavelength of radiation. In a lamp heated with 60-cps power the modulation amplitude may become rather large (10% or more) as the wavelength of radiation decreases toward the ultraviolet region. Therefore, when an ac-heated lamp is used in photometric scanning procedures it is necessary to consider the modulation if transmission measurements are made. Some measurements of modulation amplitude vs wavelength are given for two types of 100-w tungsten-filament lamp heated with 60-cps power.

The ratio of the modulation amplitude over the complete spectrum to that at a specific wavelength is proportional to the product of temperature and specific wavelength; hence a method of measuring temperature of an ac-heated filament is obtained.

© 1957 Optical Society of America

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