The Darley D-200 was an evolution of the long running C-811 3-bulb signal. The D-200 used nearly all of the same hardware as the C-811 except that it had a separate bulb behind every lens. By World War II many states required that new traffic signals have each lens independently lighted. While Darley still offered its familiar C-811 3-bulb signal, the D-200 provided a simple but reliable signal that met the requirements of every state.
Two advantages came with a 12 bulb signal. All four directions could have red at the top and green at the bottom. Also Darley was able to offer a "split amber" option, where the amber lights only lit up on sides where the signal was changing from green to red. Since the on-board controller only had four contacts, yellow indications always overlapped the green indications.
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Breaking the signal down for restoring
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