A flat refractive collimator assembly including a light guide and a light source, for example, an LED. The sides of the light guide defines a collimating reflective surface having a paraboloidal shape with a collimating focal point placed on the axis of the light guide. The central portion of the light guide defines a main reflective surface having a virtual focal point, which is substantially similar to the collimating focal point. The collimating reflective surface is a paraboloidal surface or is formed as a plurality of paraboloidal segments having various focal lengths and having a common collimating focal point. The collimating reflective surface can also include spread optics.