The history of Bausch and Lomb sunglasses started roughly with the RB lenses. RB stands obviously for Ray Ban.
RB-3 is the widely known green constant density lens. Its predecessors RB-1 and RB-2 are less know. RB-1 light green, RB-2 slightly darker, and RB-3 the darkest variety. RB-1 and RB-2 can only be found in really old models.
RB-3 lenses can be found in constant density, Top Gradient Mirrored, Double Gradient Mirrored and Full Mirrored.