What are the applications of a blackbody?
As the radiation level of a blackbody only depends on its temperature and is well-known through the Planck’s law, blackbodies are used as optical reference sources for optical sensors. Practically, as the temperatures values for blackbodies emitting over the visible range are very high and as, consequently, this leads to very expensive sources compared to classical lamps, the blackbodies are mainly used over the infrared spectral range starting from 1 µm. That’s why blackbodies are also known as Infrared Reference Sources.
The main applications are of course IR sensors calibration and their specifications measurement.