Read this from page 26 of the USCG District 8 Gulf 2007 Special Notice. It address fishing vessel's offshore, but the same rules apply.
IMPROPER USE OF SEARCHLIGHTS AND FLOODLIGHTS AT SEA
The Coast Guard has received reports that fishing vessels which use high intensity lights when setting and retrieving gear are routinely leaving them lit at all times when the vessel is underway. Although these lights may make a vessel easier to locate at great distances, improper use could interfere with the safe navigation of vessels. This may constitute a violation of the International Regulations of Preventing Collisions at Sea, 1972 (72 COLREGS) if the glare of such lights:
(a) Interferes with the night vision of mariners operating in the vicinity and the keeping of a proper lookout - Rule 5 and 20 (proper lookout).
(b) Obscures the navigation lights of the vessel, making it difficult to determine a vessel’s heading and type of operation - Rule 20 (impair distinctive character of navigation lights).
(c) Makes it difficult for mariners to identify aids to navigation and their geographical location in the vicinity of the vessel using these lights - Rule 36 (mistaken for any aid to navigation or embarrass another vessel).
Several reports indicated a vessel using sodium vapor floodlights was mistakenly reported as a vessel on fire, which resulted in a search and rescue response to a false alarm. The use of these high intensity lights may ultimately reduce the level of vigilance on the part of other mariners, which could result in an actual distress situation not being reported or answered. This notice does not prohibit a vessel from using any lights that cannot be mistaken for the lights specified in the 72 COLREGS. Mariners are cautioned that all types of high intensity lights when used at sea must be properly directed or adequately screened to ensure that under any conditions such lights will not embarrass another vessel, be misinterpreted, or illuminate beyond the immediate vicinity of the vessel. When these lights are not being used for a specific task they should be extinguished.
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