Which of the following must you do when anchoring at night?

When anchoring at night, displaying an all-around white light is essential for safety and visibility. This light serves multiple purposes: it alerts other vessels to your presence, helping to prevent collisions, and it ensures that your boat can be seen from all directions, which is particularly important in low visibility conditions. The all-around white light should be on from sunset to sunrise, as it conforms to navigation rules that are in place to ensure safety on the water.

Other lighting options, such as turning off all lights or using specific colored lights, do not provide the necessary visibility required by law. Flashing lights could confuse other boaters about your intentions or location, which is not advisable when you are securely anchored. Thus, using the all-around white light is the proper protocol when anchoring at night.