A flat or substantially flat luminous structure including two walls having main faces facing one another and defining an internal space, a light source placed in the internal space and a power supply for the light source, and at least one substantially transparent part or an overall transparent part forming at least one light well. The structure is capable of illuminating via at least one luminous region of at least one of the main faces, an element having a reflective surface that reflects visible light, placed facing at least one part of the luminous region. The element is switchable and the reflective surface is capable of becoming a substantially transparent surface or an overall transparent surface over at least one area, and vice versa.