The invention provides a reflector (2) comprising a reflector wall (20), the reflector wall (20) comprising a first wall surface (22) and a second wall surface (23) defining said reflector wall (20), the reflector wall (20) comprising a light transmissive material (21), wherein the reflector wall (20) has a first dimension (d1) and a second dimension (d2) defining a first reflector wall area, wherein each wall surface (22,23) comprises a plurality of parallel arranged elongated corrugations (210), wherein the corrugations have corrugation heights (h2) relative to recesses (220) between adjacent corrugations (210) and corrugation widths (w2) defined by the distance between adjacent recesses (220) at the respective wall surfaces (22,23), wherein the corrugations (210) have curved corrugation surfaces (230) between said adjacent recesses (220) having corrugation radii (r2) at the respective wall surfaces (22,23), and wherein over at least part of one of the first dimension (d1) and the second dimension (d2) one or more of (i) the corrugation heights (h2), (ii) the corrugation widths (w2), (iii) the corrugation radii (r2), and (iv) a shortest top-top distance (w12) of corrugations tops (211) configured at different wall surfaces (22,23) vary over said wall dimension (d1,d2) for at least one of the wall surfaces (22,23). The reflector (2) has a first end (3) and a second end (4), wherein a third distance (d3) between the first end (3) and the second end (4) is bridged by one or more reflector walls (20), wherein the one or more reflector walls (20) are configured tapering from the second end (4) to the first end (3), and wherein the reflector (2) has a reflector cavity (5).