The invention provides an arrangement (1) comprising a device (1000), wherein the device (1000) comprises a luminescent material comprising element (100) and a light transmissive element (200), wherein: (a) the device (1000) has a first device axis (A1); (b) the luminescent material comprising element (100) comprises a luminescent material (110) configured to emit luminescent material light (111) upon irradiation with first light (11), wherein the luminescent material comprising element (100) has a first length (L1) and a characteristic first dimension (D1) perpendicular to the first length (L1), wherein D1/L1