What type of track circuit is indicated when the light is not illuminated?

When the light is not illuminated in relation to track circuits, it indicates a non-occupied track circuit. This means that the section of track in question is clear and free of any trains or rolling stock. In the context of railway operations, non-occupied track circuits are crucial for ensuring safety by verifying that sections of track are available for train movement.

A non-occupied track circuit typically does not trigger an indication light because it signifies that there is no electrical path created by the presence of a train, which would normally activate the light to show that the track is occupied. This functionality is vital for the effective management of train movements, preventing collisions and ensuring that operators are aware of the current status of the tracks.

In contrast, an occupied track circuit would illuminate the light to indicate that the track is in use, while a ghost circuit refers to an erroneous indication caused by electrical interference or faults. A signal failure circuit would indicate a problem with the signaling system itself, not just the status of the track.