An illumination device, comprising: at least one light-emitting element, wherein the at least one LEE comprises a plurality of light emitting diodes (LEDs) arranged in a row; a light guide comprising two opposing planar surfaces both extending from a first end to a second end, the light guide being positioned to receive at the first end light emitted by the least one LEE and guide it between the surfaces to the second end in a forward direction that is orthogonal to the row; and an optical extractor optically coupled to the light guide at the second end, the optical extractor comprising: a first optical interface (242; 244), wherein the first optical interface is adapted to redirect a first portion of light exiting the light guide, and wherein at least portions (2455'; 2455", 245) of the first optical interface are adapted to transmit a second portion of the light exiting the light guide in the forward direction; a second optical interface (246; 248), wherein the second optical interface is curved and configured to transmit light reflected by the first optical interface in a backward direction opposing the forward direction, wherein the second interface is concave relative to a propagation direction of reflected light and extending from the first interface to at least one of the first side surface or the second side surface of the light guide. at least one light-emitting element, wherein the at least one LEE comprises a plurality of light emitting diodes (LEDs) arranged in a row; a light guide comprising two opposing planar surfaces both extending from a first end to a second end, the light guide being positioned to receive at the first end light emitted by the least one LEE and guide it between the surfaces to the second end in a forward direction that is orthogonal to the row; and an optical extractor optically coupled to the light guide at the second end, the optical extractor comprising: a first optical interface (242; 244), wherein the first optical interface is adapted to redirect a first portion of light exiting the light guide, and wherein at least portions (2455'; 2455", 245) of the first optical interface are adapted to transmit a second portion of the light exiting the light guide in the forward direction; a second optical interface (246; 248), wherein the second optical interface is curved and configured to transmit light reflected by the first optical interface in a backward direction opposing the forward direction, wherein the second interface is concave relative to a propagation direction of reflected light and extending from the first interface to at least one of the first side surface or the second side surface of the light guide. a first optical interface (242; 244), wherein the first optical interface is adapted to redirect a first portion of light exiting the light guide, and wherein at least portions (2455'; 2455", 245) of the first optical interface are adapted to transmit a second portion of the light exiting the light guide in the forward direction; a second optical interface (246; 248), wherein the second optical interface is curved and configured to transmit light reflected by the first optical interface in a backward direction opposing the forward direction, wherein the second interface is concave relative to a propagation direction of reflected light and extending from the first interface to at least one of the first side surface or the second side surface of the light guide.