A backlight unit comprising: a light guide layer having a front face and a rear face, the light guide layer comprising a plurality of extraction features disposed along the rear face of the light guide layer; a first cladding layer adhesively secured to the rear face of the light guide layer; a plurality of turning structures disposed along the first cladding layer; and a second cladding layer adhesively secured to the front face of the light guide layer; wherein the first cladding layer has a first refractive index lower than a guide refractive index of the light guide layer, and the second cladding layer has a second refractive index lower than the first refractive index; the backlight unit further comprising a concentrator disposed along an edge of the light guide layer into which the light is injected, the concentrator being configured such that the light undergoes total internal reflection from the front face until encountering at least one of the plurality of extraction features; wherein each extraction feature is shaped such that the light encountering the respective extraction feature exits the light guide layer either by passing through the extraction feature or after reflection off of the extraction feature and subsequent reflection off of the front face, each extraction feature having a face oriented at a shallow angle relative to the rear face, the shallow angle falling within a range of 1 degree to 5 degrees; and the second refractive index is offset from the guide refractive index such that the light encountering the front face after reflection off of the rear face or one of the extraction features does not pass through the front face. a light guide layer having a front face and a rear face, the light guide layer comprising a plurality of extraction features disposed along the rear face of the light guide layer; a first cladding layer adhesively secured to the rear face of the light guide layer; a plurality of turning structures disposed along the first cladding layer; and a second cladding layer adhesively secured to the front face of the light guide layer; wherein the first cladding layer has a first refractive index lower than a guide refractive index of the light guide layer, and the second cladding layer has a second refractive index lower than the first refractive index; the backlight unit further comprising a concentrator disposed along an edge of the light guide layer into which the light is injected, the concentrator being configured such that the light undergoes total internal reflection from the front face until encountering at least one of the plurality of extraction features; wherein each extraction feature is shaped such that the light encountering the respective extraction feature exits the light guide layer either by passing through the extraction feature or after reflection off of the extraction feature and subsequent reflection off of the front face, each extraction feature having a face oriented at a shallow angle relative to the rear face, the shallow angle falling within a range of 1 degree to 5 degrees; and the second refractive index is offset from the guide refractive index such that the light encountering the front face after reflection off of the rear face or one of the extraction features does not pass through the front face.