Right to light is a form of easement in English law that gives a long-standing owner of a building with windows a right to maintain the level of illumination. It is based on the Ancient Lights law. The rights are most usually acquired under the Prescription Act 1832.Wiki
The use of the 0.2 per cent standard does not appear to be based on empirical investigations involving human perceptions of adequate light. No evidence exists of the investigations reputedly undertaken by Percy Waldram during the early twentieth century. Waldram's own writings suggest that the standard began as a “rule of thumb” and was only later justified by reference to other independent reports. These generally do not support the use of the standard and, in any event, were soon superseded by other reports that concluded that it was too low. There is a lack of reliable evidence to justify the original adoption of the 0.2 per cent figure, and many of the assumptions underpinning modern rights to light practice are found to be based on inaccurate information.
Findings from: Progressing the rights to light debate: Part 2: the grumble point revisited by Paul Chynoweth, University of Salford, Salford, UK
A consultation meeting with the Law Commission as part of the Law Society’s consultation process on Rights to Light
Professor Elizabeth Cooke, Law Commissioner
Professor John Mardaljevic, Loughborough University
Professor Peter Tregenza, Sheffield University
University College London, 8 May 2013