GN01/21 has been produced to clarify metrics introduced in the previous version, with regards to when more detailed requirements should be applied and how they can be assessed.

Most of the previous version remains; this is a ‘light-touch’ update. It provides further clarification on the assessment of source intensity and includes some worked examples. It also advises on the definition of and application of curfews; this is when more stringent lighting controls could be specified. Finally, the update suggests when the more difficult to measure metric of upward reflected light or Upward Flux Ratio (UFR) should be considered and discusses its calculation.

View the latest updated document here.