A device and method for exposing light sensitive substrates to a concentrated light source. The device is suitable for curing substances such as photosensitive sensitive inks, adhesives, and photographic elements. Ultraviolet or visible light is emitted from an array of LED's, and then directed by an array of light guides to a light concentrator having a light input region along its length. The light is then concentrated and emitted from a light output region along the length of the light concentrator to a photosensitive target to be exposed.