An illuminating instrument for diagnostics, therapy or surgery of a body part, comprising: at least one optical fiber for transmitting electromagnetic radiation directly from an electromagnetic radiation source to the body part; and a housing which supports the optical fiber ; the optical axis of the light-output end of the optical fiber circumferentially extends in an illumination portion in the housing which is annular shaped and arranged to face the body part; the optical fiber in the illumination portion has one or more diffusing regions for diffusing the electromagnetic radiation to the outside of the optical fiber through the circumferential surface thereof, a coupling device which supports the electromagnetic radiation source for generating the electromagnetic radiation, characterized by further comprising: a conversion means which is supported by the housing without directly contacting the electromagnetic radiation source , and arranged between the diffusing regions and the body part for converting the electromagnetic radiation into visible light for illuminating the body part, and wherein the light-entrance end of the optical fiber is directly optically connected with the electromagnetic radiation source , wherein the conversion means is outside an optical interface between the light-entrance end of the optical fiber and the electromagnetic radiation source . at least one optical fiber for transmitting electromagnetic radiation directly from an electromagnetic radiation source to the body part; and a housing which supports the optical fiber ; the optical axis of the light-output end of the optical fiber circumferentially extends in an illumination portion in the housing which is annular shaped and arranged to face the body part; the optical fiber in the illumination portion has one or more diffusing regions for diffusing the electromagnetic radiation to the outside of the optical fiber through the circumferential surface thereof, a coupling device which supports the electromagnetic radiation source for generating the electromagnetic radiation, characterized by further comprising: a conversion means which is supported by the housing without directly contacting the electromagnetic radiation source , and arranged between the diffusing regions and the body part for converting the electromagnetic radiation into visible light for illuminating the body part, and wherein the light-entrance end of the optical fiber is directly optically connected with the electromagnetic radiation source , wherein the conversion means is outside an optical interface between the light-entrance end of the optical fiber and the electromagnetic radiation source . a conversion means which is supported by the housing without directly contacting the electromagnetic radiation source , and arranged between the diffusing regions and the body part for converting the electromagnetic radiation into visible light for illuminating the body part, and wherein the light-entrance end of the optical fiber is directly optically connected with the electromagnetic radiation source , wherein the conversion means is outside an optical interface between the light-entrance end of the optical fiber and the electromagnetic radiation source . <EOS>