any of various lights required to be displayed by a vessel or aircraft operating between sunset and sunrise.
one of several white, red, or green lights displayed by vessels operating at night
Collins English Dictionary - Complete & Unabridged 10th Edition
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The modification to the headlight system shall not interfere or cause any feedback with the existing daytime running light system.
In addition, the ship was running light because of all the fuel consumed during this cruise.
And then that's the mast headlight and then this is called the running light.