The invention relates mainly to an optical guide for diffusing a light radiation through a surface, which is essentially characterized in that it includes a base (3,31) comprising or able to hold at least one diffusion rod (2, 2a; 35a, 35b, 35c) whose lower diffusion end (7, 7a; 38a, 38b, 38c) protrudes from said base (3) and is intended to be applied on or near said surface, and whose upper collecting end (6,6a; 37a, 37b, 37c) is intended to be located near and opposite a power supplied light source (36a, 36b, 36c), and in that the diffusion rod (2, 2a; 35a, 35b, 35c) comprises a material able to transmit light from its collecting end (6,6a; 37a, 37b, 37c) up to its diffusion end (7, 7a; 38a, 38b, 38c).
The invention also relates to an irradiation module and to an irradiation device adapted to the transcranial and/or transcutaneous irradiation by light radiation.