Why do offshore lighthouses use contrasting red or black bands?

Offshore lighthouses use contrasting red or black bands to serve as a daymark, ensuring the structure remains conspicuous and easily identifiable against the prevailing background of the open sea or light-colored surroundings.1

While lighthouses are primarily used for coastal navigation and warning mariners of hazards, their physical appearance is critical for daytime identification. Unlike shore-based lighthouses, which are typically painted white to stand out, offshore structures require these bold, contrasting patterns to ensure they are clearly visible to navigators during daylight hours.21