Text in force at CS27-10: from CS27-0, effective 14 Nov 2003.
(a) Each riding light required for water operation must be installed so that it can:
(1) Show a white light for at least 3.7 km (two nautical miles) at night under clear atmospheric conditions; and
(2) Show a maximum practicable unbroken light with the rotorcraft on the water.
(b) Externally hung lights may be used.
ED Decision 2003/015/RM · Source