The document addresses simplification of the definition of “apparent surface” and single lamp distance requirements in UN R48. It presents a new CAD-based concept defining apparent surface using light emitting surface with clear outer lens disregarded. The document notes that current regulation allows multiple ways to define apparent surface resulting in different distances, with existing approvals having distances significantly larger than 75mm between distinct parts without known safety issues. GTB agrees on simplifying the apparent surface definition to describe function contours as seen by road users, while acknowledging this should not restrict possible designs. The document references a 1999 INF Milano study concluding symmetric appearance is relevant for vehicle identification and larger distances are acceptable for symmetric compared to asymmetric constellations.

This document discusses single lamp distance requirements in context of Apparent Surface simplification pursuant to discussions with Contracting Parties. The current 75mm separation value was not based on studies but on considerations. A 1999 IENGF Milano study concluded that larger distances are acceptable for symmetric constellations, with AFS lighting units spaced up to 200mm. A minimum 600mm separation is mandatory if right and left mounted functional unit identification is required. No evidence of increased accident risk, misidentification of signal, reduced conspicuity, or regulatory enforcement issues from current single lamp separation distances exists. The simplified CAD-based Apparent Surface concept will be based on light emitting surface with clear outer lens disregarded. GTB suspended work on this topic due to insufficient consensus and difficult stakeholder alignment, pending additional information on single lamp separation distance.