A light concentration device includes: a plate including two principal faces and an edge between the two principal faces, a refractive index gradient existing between the two principal faces, and a diffraction grating functioning in reflection or semi-reflection that cooperates with one of the principal faces of the plate having the highest refractive index, the principal face having the lowest refractive index forming a front entry face for the light, at least one exit zone for the light being disposed on the edge.