The invention relates to a light diffuser casing comprising an enclosure defining a cavity and provided with a closable opening configured to enable a headlamp to be inserted inside the casing. A light diffuser is arranged in the casing to receive a light beam coming from the headlamp and to make said beam diffuse on the enclosure. The light diffuser is made from a translucent or transparent material so that said beam passes through it, and the enclosure is made from a translucent material. The invention also relates to a method for using the casing.