In the case of a mirage, it is REFRACTION, not reflection, creating a similar effect. The hot surface warms the air immediately above it to a higher temperature than the air higher up. A light ray grazing the surface under thosecircumstances is bent, or refracted, upward. That's because light travels faster in warmer, less dense, air than in denser cold air. The faster motion of the lower part of a light ray speeds ahead of the upper part, causing it to bend (refract) upward.When the refracted light ray meets your eye, it appears to be coming from the road surface instead of the distant sky. A reflected light ray follows a similar path, so the refracted ray is interpreted as a reflected one and a 'Mirage' is seen.