Ancient Lights

'Ancient lights' is a doctrine in English property law providing a right to light, where a property owner who has enjoyed natural light through a window for at least 20 years can legally prevent neighbours from blocking it. Formalised by the Prescription Act 1832, this law ensures 'adequate illumination,' often marked by signs on older buildings to warn developers.

You can see the sign above the window on the white flank wall of the building here.

The big question is how to measure the adequacy of illumination to determine whether a proposed obstruction compromises 'adequate illumination?' There is a science and a convention with rules that enable professionals to calculate to what extent a building may have its illumination compromised. The calculations involve the angle of the sun at different times of the year, the height and distance of proposed adjoining buildings, etc.

When submitting plans for a development to the Local Authority, where the development overlooks existing buildings, you will sometimes see a document that sets out the what and the why of how the proposal does not compromise light, whether an 'Ancient lights' sign has been displayed or not.