Abstract: A nondestructive method of temperature measurement of arc tubes in high intensity discharge lamps has been developed using through the glass thermal imaging. This obviates the need to break the lamp outer jackets in order to gain access to the arc tube surface. A narrow band filter centered at 3.9 $mu@m is used to image the lamp. Since the spectral radiance properties of the materials arc wavelength dependent, the filter enables a more accurate measurement compared to the wideband imaging routinely employed (3 - 5 $mu@m). The path radiance equation was derived for the arc tube and bulb configuration. The radiance due to the arc tube alone is extracted after accounting for the glass contributions to the path equation. For this purpose, the temperature of the glass bulb is determined using a long wave filter (8 - 12 $mu@m). System calibration curves are used to convert from temperature to radiance units and vice versa. This method has been found to yield arc tube surface temperatures with relatively high accuracy.!2
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