Abstract: A modular lighting system for illuminating products supported upon various vertically arranged shelves of a display unit includes a housing attached to a first shelf, with the housing including at least one transparent panel which permits an internal illumination source to light products supported upon at least one of the first shelf, a shelf arranged directly above the first shelf and a shelf disposed directly below the first shelf. Most preferably, the light illuminating from the housing is directed so as to effectively, entirely illuminate product support surfaces associated with both the first shelf and the shelf directly below such that the display of products supported anywhere from the front to the back of these shelves is enhanced. This front-to-back lighting function can be achieved in various ways, such as by employing direct, reflective and refractive lighting techniques.