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I think this is the information you need!Ancient lights is a term of property law in England. It gives a long-standing owner of a building with windows a right to maintain the level of illumination. A Prescription Act of 1832 created it.
In effect, the owner of a building with windows that have received natural daylight for 20 years or more is entitled to forbid any construction or other obstruction that would deprive him of that illumination. Neighbors cannot build anything that would block the light without permission. The owner may build more or larger windows but cannot enlarge his new windows before the new period of 20 years has expired.
After World War II, owners of buildings could gain new rights by registering properties that had been destroyed in bombings and the period was temporarily increased to 27 years.
In the center of London, near Chinatown and Covent Garden, particularly in back alleyways, signs saying "Ancient Lights" can be seen marking individual windows.