What is a Bolometer?

            Bolometer is an instrument that is used to measure radiation temperature. It is a kind of Resistance Bridge. Its one arm consists of a blackened metal strip. When the radiations fall on the metal strip the temperature rises. This increase in temperature measured by a bolometer. This is a very sensitive instrument.


            A U.S. scientist, Samuel P. Langely invented this instrument in 1880. In this first bolometer, a Wheatstone bridge was used along with a galvanometer that produced a deflection proportional to the intensity of the radiation. Since then several other thermal devices have been developed but bolometer remains one of the most effective and convenient infrared detectors. It is because it does not need cooling and can be operated with great ease.

            Now the question arises, what is the principle of working of this instrument? The principle on the basis of which a bolometer operates is that a temperature changes is produced by the absorption of radiation this causes a change in electrical resistance of the material used in the fabrication of the bolometer. This change in resistance can be used to sense radiation.

            There are several types of bolometer in use today. One type has two strips bridge the circuit, their electrical resistance changes. The change of resistance can be used to measure the temperature. This instrument is so sensitive that it can detect changes in temperature as small as 0.001 degree centigrade.

            Another type of bolometer known as spectrum bolometer consists of a single strip of metal. It is used for examining the distribution of intensity of radiation in a spectrum.