Conventional side dots on guitar and similar instrument fingerboards are typically formed of mother-of-pearl or other reflective materials so a player can locate fret positions under ambient light. In low-light performance conditions the markers can be difficult to see. Prior systems have used fiber-optic strands routed through the neck to illuminate markers (for example, U.S. Patent No. 3,943,815) or external fiber strands adhered to the top surface of the neck (for example, U.S. Patent No. 5,373,768). Many such approaches either alter the traditional look and feel of the markers, require external attachments, or do not provide a dual-mode design in which the markers continue to function as ordinary reflective side dots when the lighting system is switched off. There remains a need for a system that is manufactured into the instrument at the time of construction, illuminates the side dots when desired with selectable brightness, and leaves the markers fully functional.