A vessel may exhibit lights other than those prescribed by the Rules as long as the additional lights __________.

A vessel may exhibit lights other than those prescribed by the Rules as long as the additional lights do not interfere with the keeping of a proper look-out. This principle is rooted in the safety of navigation and collision avoidance. It is essential for vessels to maintain an adequate lookout, which involves using all available means to observe the surroundings effectively. If additional lights were to confuse or distract the crew, it could lead to dangerous situations, such as collisions or failure to notice other vessels or navigational hazards.

The emphasis on not interfering with proper lookout ensures that any lighting system remains effective in allowing the crew to perceive and assess their surroundings without unnecessary distraction. Other options such as the color of the lights, signaling for distress, or periodic flashing do not directly address the critical importance of maintaining a clear and effective lookout while navigating. Hence, the focus on ensuring that additional lights do not impede this essential practice is paramount.