Light emitting device including a light absorbing cladding region on edges of a core layer of a film-based lightguide

A light emitting device comprises a lightguide formed from a film with a core layer, a light emitting region, a light mixing region, at least one light source, and a light absorbing cladding region on at least one lateral edge of the core layer. In one embodiment, the cladding region is on the lateral edges of the core layer in the light mixing region. The light absorbing material in the cladding region may absorb light from the at least one light source propagating in the cladding region at an angle greater than 40 degrees to the optical axis. The difference in refractive index for the core material and cladding material may be between 0.001 to 0.01. The full angular width at half maximum intensity of light exiting the light emitting region may be less than 60 degrees in air in a first illumination plane.