Ancient Lights Law and Legal Definition
Ancient lights refer to windows which have been opened for twenty years or more, and enjoyed without interruption by the owner of the house. This comes from a common law principle by which a land owner acquires after 20 years of uninterrupted use, an easement preventing a neighbor from building an obstruction that blocks light from passing through the landowner’s window. This is referred to as the Ancient lights or Ancient windows doctrine.
An action can be brought against a person who obstructs an ancient light. Total deprivation of light is not necessary to sustain an action. If a party cannot enjoy the light in a free and ample manner as s/he did before s/ he may sustain the action. However, the privilege is lost when a window has been completely blocked up for twenty years. An abandonment of the right by express agreement, or by acts from which abandonment may be inferred, will also deprive the party having such ancient light of his right to it.
This doctrine is rarely applied in the U.S.