The 78th session of the GRE Informal Working Group on Simplification of UN Lighting and Light-Signalling Regulations was held in Brussels, 10-12 June 2026. SLR decided not to include a new Part 7 on Colour-fastness in Annex 6 to Regulation 150-01 and will submit a consolidated correction proposal to GRE-95. Discussion on apparent surface definitions and single lamp distance requirements will resume at SLR-79, with wider consideration of related topics including glare and direction indicator visibility. Baseline documents for Regulations 48, 53, 74, and 86 were reviewed and updated versions will be prepared for the next session. The next SLR meeting will be held in Tokyo on 7-11 September 2026.