An optical warning system comprising a light head that includes a light source emitting light from a light-emitting area, the light propagating through an optical diffuser to provide a visual warning signal to an observer remotely located from the optical warning system, characterized in that system further comprises: a Fresnel optic array positioned between the optical diffuser and the light-emitting area, the Fresnel optic array spaced apart from and spatially aligned with the light-emitting area to receive the light emitted from the light-emitting area and having a principal axis and a focal point, and the Fresnel optic array having first and second opposite major surfaces, of which the first major surface has multiple concentric ring facets positioned nearer to the optical diffuser and of which the second major surface is flat and positioned nearer to the light-emitting area; the multiple concentric ring facets forming separate inner and outer groups, the concentric ring facets in the inner group having facet spacings that are greater than facet spacings of the concentric ring facets in the outer group; each of the multiple ring facets in the outer group occupying an annular region in which a draft facet and an adjacent optical facet are joined to form a rounded peak, the draft facet inclined at a draft angle and the rounded peak defined by a peak radius, the draft angle and peak radius set to values that are coordinated to cause incident light emitted from the light-emitting area to propagate through the optical facet and not through the draft facet and the rounded peak thereby to increase optical transmission efficiency of the Fresnel optic array by reducing light lost to scattering by the rounded peak in forming a collimated light beam; and the light source including a pair of light-emitting diodes, the pair of light-emitting diodes positioned at substantially equal distances from and on opposite sides of the focal point of the Fresnel optic array and emitting beams of light of different first and second colors, and the Fresnel optic array producing, from the beams of light of different first and second colors emitted by the pair of light-emitting diodes, two substantially collimated light beams propagating off-axis compared to the principal axis of the Fresnel optic array, and the diffuser dispersing the two substantially collimated light beams to form a diffused light intensity pattern that is symmetrical about, and has a peak intensity that lies on, the principal axis of the Fresnel optic array. a Fresnel optic array positioned between the optical diffuser and the light-emitting area, the Fresnel optic array spaced apart from and spatially aligned with the light-emitting area to receive the light emitted from the light-emitting area and having a principal axis and a focal point, and the Fresnel optic array having first and second opposite major surfaces, of which the first major surface has multiple concentric ring facets positioned nearer to the optical diffuser and of which the second major surface is flat and positioned nearer to the light-emitting area; the multiple concentric ring facets forming separate inner and outer groups, the concentric ring facets in the inner group having facet spacings that are greater than facet spacings of the concentric ring facets in the outer group; each of the multiple ring facets in the outer group occupying an annular region in which a draft facet and an adjacent optical facet are joined to form a rounded peak, the draft facet inclined at a draft angle and the rounded peak defined by a peak radius, the draft angle and peak radius set to values that are coordinated to cause incident light emitted from the light-emitting area to propagate through the optical facet and not through the draft facet and the rounded peak thereby to increase optical transmission efficiency of the Fresnel optic array by reducing light lost to scattering by the rounded peak in forming a collimated light beam; and the light source including a pair of light-emitting diodes, the pair of light-emitting diodes positioned at substantially equal distances from and on opposite sides of the focal point of the Fresnel optic array and emitting beams of light of different first and second colors, and the Fresnel optic array producing, from the beams of light of different first and second colors emitted by the pair of light-emitting diodes, two substantially collimated light beams propagating off-axis compared to the principal axis of the Fresnel optic array, and the diffuser dispersing the two substantially collimated light beams to form a diffused light intensity pattern that is symmetrical about, and has a peak intensity that lies on, the principal axis of the Fresnel optic array.