14 CFR § 25.1399 - Riding light.
§ 25.1399 Riding light.
(a) Each riding (anchor) light required for a seaplane or amphibian must be installed so that it can—
(1) Show a white light for at least 2 nautical miles at night under clear atmospheric conditions; and
(2) Show the maximum unbroken light practicable when the airplane is moored or drifting on the water.
(b) Externally hung lights may be used.