The invention mainly concerns an optical guide for diffusing light radiation through a surface, which is essentially characterised in that it comprises a base (3, 31) comprising or capable of holding at least one diffusion rod (2, 2a； 35a, 35b, 35c), the diffusing bottom end (7, 7a； 38a, 38b, 38c) of which protrudes from said base (3) and is intended to be applied on or close to said surface, and the collecting top end (6, 6a； 37a, 37b, 37c) of which is intended to be situated close to and facing an electrically powered light source (36a, 36b, 36c), and in that the diffusion rod (2, 2a； 35a, 35b, 35c) comprises a material capable of transmitting the light from the collecting end (6, 6a； 37a, 37b, 37c) of same to the diffusing end (7, 7a； 38a, 38b, 38c) of same. The invention also concerns an irradiation module and an irradiation device suitable for transcranial and/or transcutaneous irradiation by light radiation.
