An optical sight includes an optical train having an optical path therethrough, an entrance, and an exit. A reticle is visible through the exit of the optical path. An unpowered reticle illumination source has a first light source that illuminates the reticle responsive to the level of ambient light, and a second light source that illuminates the reticle with an unpowered light source. The reticle illumination source preferably has a scintillation material positioned so that ambient light entering the ambient-light receiver is incident upon the scintillation material, whereupon the scintillation material responsively emits secondary light. A light-gathering prism receives the secondary light and has a diffusing surface disposed to illuminate the reticle using the secondary light. An unpowered light source is positioned to emit light through the diffusing surface to be incident upon the reticle. The unpowered light source may be a tritium light source.