PURPOSE: To provide an essentially light non-directional probe coupled with fish and used for detecting and measuring the light quantity under sea level by using an optical fiber having a core including fluorescent dye. CONSTITUTION: This probe 1 obtains an optical fiber 2 coupled with a light detector 3 in a housing 4 at one end. A light detector 3 for measuring the light quantity received from an optical fiber 2 and an electric circuit for recording and storing the data are surrounded by the housing 4, and the housing 4 is mounted inside fish. The optical fiber 2 is protruded in sea water, receives light, and transmits it to the light detector 3. The optical fiber 2 is covered the sheath of a translucent coating 5 and is protected from sea environment. The optical fiber 2 includes fluorescent dye having narrow excitation spectrum. A light having a certain wavelength in the excitation spectrum is incident to the side face of the optical fiber 2, the dye is excited, fluorescence light is emitted, and the light with longer wavelength is re-emitted. The re-emitted light is transmitted toward the light detector 3, is measured, and is recorded.
PROBE FOR DETECTING LIGHT UNDER SEA LEVEL