How does a searchlight signal work?

Answer 1

A searchlight signal is a small unit that uses one lamp and a set of 3 lenses that move similar to the way that semaphore signals moved. With no electricity on the controls, the signal displays the Red lens. When elecricity is applied in one direction, the armature tilts left or right, and displays a different lens (typically yellow or green). The opposite electricity is applied (positive and negative reversed) it tilts the other way and shows the other color lens.

Because it is a mechanical device, the railroad is required to have special "check" circuits to make sure it moves properly and has not been damaged. This makes it a very high maintenance signal and is a major reason that most railroads have either already removed them, or eventually will.