Discovery of the luminescence of water during irradiation of radiation at a lower energy than the Cherenkov light threshold

It is widely believed that light is not emitted in water during irradiation of radiation at energies lower than the Cherenkov light threshold. Contrary to this consensus, we discovered that light (luminescence) is emitted in water during irradiation of radiation, and imaging of this luminescence was possible. In this review, the author describes the optical images obtained for various types of radiation, their characteristics and origins, and potential applications of the luminescence of water during irradiation at a lower energy than the Cherenkov light threshold. The author also describes the luminescence of other transparent materials and future prospects of the discovered luminescence.