ancient lights

 
Pronunciation: /eɪnʃəntˈlʌɪts/

plural noun

[treated as singular] English Law
  • the right of access to light of a property, established by custom and used to prevent the construction of buildings on adjacent property which would obstruct such access.

Origin:

mid 18th century: from lights meaning 'light from the sky'. In England the sign ‘Ancient Lights’ was often placed on a house, adjacent to a site where a high building might be erected