Under which circumstance must the headlight be dimmed when stopped close behind a train?

Dimming the headlight when stopped close behind a train is crucial for safety and operational reasons. When a locomotive is stationary behind another train, maintaining a bright headlight can cause distraction or discomfort to the crew of the train in front. It can also create confusion for other railroad personnel and may interfere with their ability to see signals or communicate effectively.

This practice helps to ensure that all crews are focused on their respective tasks without unnecessary distractions that could lead to safety concerns. By dimming the headlight, you are adhering to good operating practices that promote a safer working environment on the railroad. Other scenarios presented in the options may involve different considerations for headlight use, but specifically when stopped close behind another train, dimming the headlight is a standard procedure to facilitate safe operations.