Complex sentence: The original system used asymmetric rows of 4 lights mimicking the positions of an upper quadrant semaphore, later the system was simplified to use rows of 3 lamps, pivoting around a common center.
Split into simpler sentences: The original system used asymmetric rows of four lights mimicking the positions of an upper quadrant semaphore. The system was later simplified to use rows of three lamps, pivoting around a common center.