When coastal blackouts hinder enemy navigation

When were coastal blackouts a good idea, and when were they less useful?

They mattered most when ships relied on visual navigation aids. Other navigation systems reduce their effect, although shore lights can still provide useful confirmation.

Darkened lighthouses, ports, and shore facilities deprive ships of recognizable points for fixing their position. Blackouts therefore have the greatest effect when crews depend on visual navigation aids. Once other navigation systems are available, removing those lights has less impact. A modern blackout could still complicate navigation by denying a visual check on the position indicated by those systems.