The　luminance　L20(S)　varies　considerably　from　time　to　time　throughout　the　day　and　obtaining　its　value　in　real-time　during　urban　tunnel　operations　is　challenging.　Thus,　the　authors　propose　a　real-time　calculation　method　that　takes　solar　illuminance　as　the　input　variable　and　couples　the　sky　and　ground　scene　luminance　into　L20　(S)　in　combination　with　a　three-dimensional　(3D)　printed　tunnel　scaled　model.　The　Luhua　road　tunnel　in　Beijing　is　taken　as　the　measurement　object.　A　3D　printed　tunnel　scaled　model　is　used　instead　of　an　actual　tunnel　to　explore　the　change　rule　of　ground　scene　luminance,　and　a　quantitative　regression　model　of　ground　scene　luminance　and　solar　illuminance　is　established.　The　calculated　values　from　the　International　Commission　on　Illumination　(CIE)　and　Perez　models　are　compared　with　the　measured　values　based　on　solar　illuminance　in　the　present　study.　The　CIE　model　with　a　smaller　error　and　easier　calculation　is　determined　as　the　sky　luminance.　The　error　rates　are　4.26%　and　6.11%　under　sunny　and　cloudy　conditions,　respectively.　The　average　error　rate　of　the　calculated　values　of　the　coupled　L20(S)　calculation　model　and　the　measured　values　in　different　seasons　and　weather　conditions　is　below　10%,　demonstrating　the　accuracy　and　applicability　of　the　real-time　calculation　method　for　tunnel　access　zone　luminance　in　all　seasons　and　weather　conditions.　©　2024　Editorial　Office　of　Tunnel　Construction.　All　rights　reserved.