The present invention introduces a new class of thin doubly collimating light distributing engines for use in a variety of general lighting applications, especially those benefiting from thinness. Output illumination from these slim-profile illumination systems whether square, rectangular or circular in physical aperture shape is directional, square, rectangular or circular in beam cross-section, and spatially uniform and sharply cutoff outside the system's adjustable far-field angular cone. Field coverage extends from +/−5- to +/−60-degrees and more in each meridian, including all asymmetric combinations in between, both by internal design, by addition of angle spreading film sheets, and angular tilts. Engine brightness is held to safe levels by expanding the size of the engine's output-aperture without sacrifice in the directionality of illumination. One form of the present invention has a single input light emitter, a square output aperture and the capacity to supply hundreds of lumens per engine. A second multi-segment form of the invention deploys one light emitter in each engine segment, so that total output lumens is determined by the number of segments. Both types of thin light distributing engines provide input light collimated in one meridian and a light distributing element that maintains input collimation while collimating output light in the un-collimated orthogonal meridian, in such a manner that the system's far-field output light is collimated in both its orthogonal output meridians. The present invention also includes especially structured optical films that process the engine's doubly collimated output illumination so as to increase its angular extent one or both output meridians without changing beam shape or uniformity.