This invention relates to a light guide (1) for a control knob, particularly an instrument panel of a vehicle. The knob is fitted with an index (3) free to move in rotation about an axis (A). The light guide (1) will be inserted between a light source (2) and the index (3) and comprises at least one entry surface (4) for light rays emitted by the light source (2), a first exit surface (6) of light rays towards the index (3) and side faces (5) inserted between the entry surface (4) and the first exit surface (6). The light guide comprises first optical means (4, 8, 15, 16) to orient received light rays approximately parallel to the rotation axis (A) of the index (3), and second optical means (5, 22, 14, 17, 18, 19, 20) to focus the previously reoriented light rays towards at least the first exit surface (6).