Optical pyrometers

A non-contact method of measuring high temperature is to match the brightness of a tungsten lamp filament with the brightness of a hot object. Instruments which use this technique, called optical pyrometers, are used to measure temperatures, such as those of hot furnaces, molten glass, nuclear blasts and the surface of the sun.

The advantage of tungsten is that its melting point is ~ 3700 K, much higher than that of iron (~ 1800 K) or copper (~ 1350 K). The brightness of the source is reduced by a screen when one is measuring even higher temperatures, such as that of the sun's surface.

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