What does the “Ancient Lights law” state?

Did you know that there’s a country in the world, where the owner of a building with windows that have received natural daylight for 20 years or more can forbid any construction or other obstruction?

This country is England and  according to English law, the “Ancient Lights law”  states that the owner of a building in the above case can forbid any construction or other obstruction that would deprive him/her of that illumination or “their portion of natural light”.