A light guide for display devices of the head-mounted or head-up type comprises: a body of the light guide (22) at least in part transparent to visible light; a coupling device (24) associated to the body of the light guide (22) and designed to couple the body (22) to an optical system (18) designed to generate an image, the coupling device (24) being obtained in such a way that the light beams coming from the optical system (18) enter the body of the light guide (22) and propagate within the body (22) by total internal reflection; and an image-extraction grating, designed to extract the light beams that propagate in the body of the light guide (22) so as to enable an observer to visualize the extracted image against a background visible in transparency through the body of the light guide (22). The extraction grating (32) is set in the proximity of one of the outer surfaces of the guide and has a saw-tooth profile. The extraction grating (32) is coated with a partially reflecting coating deposited prevalently on the surfaces of the teeth that are least inclined with respect to the surfaces (22) of the guide.