14 C.F.R. § 23.1399 Riding light.
Title 14 - Aeronautics and Space
(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 two 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.
Title 14: Aeronautics and Space
PART 23—AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES
Subpart F—Equipment
Lights
§ 23.1399 Riding light.