The invention proposes a light device casing formed by a wall made of an electrically insulating material, such as a polymer. The casing includes an inner surface forming a housing receiving a light module with a light-emitting diode and a light guide. The inner surface includes a zone reflecting light from the light module out of the casing, and a fixing zone for a control module of the light module. The light device includes a reflecting and electrically conductive coating, which covers both the reflecting zone and the fixing zone. The aluminum coating is cost-effective since it is applied in one step, and it ensures two functions, namely a reflection and a protection against the electromagnetic field.