A lighting device, comprising: an optical waveguide, comprising: a waveguide body comprising: a first waveguide body arm comprising a first portion and a second portion disposed at a non-zero angle with respect to the first portion; a second waveguide body arm comprising a third portion and a fourth portion disposed at the non-zero angle with respect to the third portion, wherein a coupling cavity is defined between the second portion and the fourth portion; and a first film disposed on a first surface of the first portion of the first waveguide body arm, wherein the first film comprises a first base and a first plurality of undercut light extraction elements disposed between the first base and the first surface, and wherein each of at least some of the first plurality of undercut light extraction elements comprises a first cross sectional curved shape; a second film disposed on a third surface of the third portion of the second waveguide body arm, wherein the second film comprises a second base and a second plurality of undercut light extraction elements disposed between the second base and the third surface, and wherein each of at least some of the second plurality of undercut light extraction elements comprises a second cross sectional curved shape; and a light source disposed adjacent to the second portion and the fourth portion such that light from the light source is totally internally reflected through the second portion and the fourth portion into the first portion and the third portion, respectively, and the light is extracted via the first plurality of undercut light extraction elements and the second plurality of undercut light extraction elements, respectively. an optical waveguide, comprising: a waveguide body comprising: a first waveguide body arm comprising a first portion and a second portion disposed at a non-zero angle with respect to the first portion; a second waveguide body arm comprising a third portion and a fourth portion disposed at the non-zero angle with respect to the third portion, wherein a coupling cavity is defined between the second portion and the fourth portion; and a first film disposed on a first surface of the first portion of the first waveguide body arm, wherein the first film comprises a first base and a first plurality of undercut light extraction elements disposed between the first base and the first surface, and wherein each of at least some of the first plurality of undercut light extraction elements comprises a first cross sectional curved shape; a second film disposed on a third surface of the third portion of the second waveguide body arm, wherein the second film comprises a second base and a second plurality of undercut light extraction elements disposed between the second base and the third surface, and wherein each of at least some of the second plurality of undercut light extraction elements comprises a second cross sectional curved shape; and a waveguide body comprising: a first waveguide body arm comprising a first portion and a second portion disposed at a non-zero angle with respect to the first portion; a second waveguide body arm comprising a third portion and a fourth portion disposed at the non-zero angle with respect to the third portion, wherein a coupling cavity is defined between the second portion and the fourth portion; and a first waveguide body arm comprising a first portion and a second portion disposed at a non-zero angle with respect to the first portion; a second waveguide body arm comprising a third portion and a fourth portion disposed at the non-zero angle with respect to the third portion, wherein a coupling cavity is defined between the second portion and the fourth portion; and a first film disposed on a first surface of the first portion of the first waveguide body arm, wherein the first film comprises a first base and a first plurality of undercut light extraction elements disposed between the first base and the first surface, and wherein each of at least some of the first plurality of undercut light extraction elements comprises a first cross sectional curved shape; a second film disposed on a third surface of the third portion of the second waveguide body arm, wherein the second film comprises a second base and a second plurality of undercut light extraction elements disposed between the second base and the third surface, and wherein each of at least some of the second plurality of undercut light extraction elements comprises a second cross sectional curved shape; and a light source disposed adjacent to the second portion and the fourth portion such that light from the light source is totally internally reflected through the second portion and the fourth portion into the first portion and the third portion, respectively, and the light is extracted via the first plurality of undercut light extraction elements and the second plurality of undercut light extraction elements, respectively.