If you have an area devoid of sunlight and there have an enclosed water stream that transports items over a packed ice block with a pressure plate on top (to stop liquids) into a lava source (also enclosed), the items being destroyed will cause light flickering of dark spots in the area. The wall on which the lava is on the opposite end of will also be affected. As seen in the images, the dark areas are completely blocked from light but still light up once items get destroyed.