A lighting unit , comprising: a back reflector , the back reflector comprising: a central region that runs longitudinally down the back reflector ; a first side region on a side of the central region; and a second side region on the side of the longitudinal region opposite the first side region, wherein the first and second side regions define a symmetrical cross-section, wherein the first side region, the second side region, and the central region are reflective; a heat sink mounted proximate to the back reflector , the heat sink comprising a mount surface that faces toward said back reflector , the region between the heat sink and the back reflector defining an interior cavity ; a plurality of light emitters disposed on the mount surface and aimed to emit light toward the back reflector , the mount surface proximate to the central region, the mount surface facing the back reflector and being configured such that the plurality of light emitters are substantially above the heat sink , and wherein the plurality of light emitters are substantially in line with the central region in a first direction; a first lens plate that extends from the heat sink to the first side region of the back reflector ; and a second lens plate that extends from the heat sink to the second side region of the back reflector , wherein the first and second lens plates define the interior cavity, characterized in that the first and second lens plates are angled with respect to the mount surface and the mount surface is offset from the back reflector such that the mount surface is entirely below a bottom edge of the back reflector in a second direction perpendicular to the first direction, so that the heat sink provides mechanical shielding of the first and second lens plates. a back reflector , the back reflector comprising: a central region that runs longitudinally down the back reflector ; a first side region on a side of the central region; and a second side region on the side of the longitudinal region opposite the first side region, wherein the first and second side regions define a symmetrical cross-section, wherein the first side region, the second side region, and the central region are reflective; a central region that runs longitudinally down the back reflector ; a first side region on a side of the central region; and a second side region on the side of the longitudinal region opposite the first side region, wherein the first and second side regions define a symmetrical cross-section, wherein the first side region, the second side region, and the central region are reflective; a heat sink mounted proximate to the back reflector , the heat sink comprising a mount surface that faces toward said back reflector , the region between the heat sink and the back reflector defining an interior cavity ; a plurality of light emitters disposed on the mount surface and aimed to emit light toward the back reflector , the mount surface proximate to the central region, the mount surface facing the back reflector and being configured such that the plurality of light emitters are substantially above the heat sink , and wherein the plurality of light emitters are substantially in line with the central region in a first direction; a first lens plate that extends from the heat sink to the first side region of the back reflector ; and a second lens plate that extends from the heat sink to the second side region of the back reflector , wherein the first and second lens plates define the interior cavity, characterized in that the first and second lens plates are angled with respect to the mount surface and the mount surface is offset from the back reflector such that the mount surface is entirely below a bottom edge of the back reflector in a second direction perpendicular to the first direction, so that the heat sink provides mechanical shielding of the first and second lens plates. <EOS>