A light source assembly includes a light guide unit and a light emitting unit. The light guide unit includes a hollow enclosure and a lens unit enclosed in the enclosure. The enclosure has a top portion, a bottom portion and a sidewall connected between the bottom portion and the top portion. Protrusions extend from an outer surface of the sidewall and coil the sidewall. A light incident surface is positioned on the bottom portion. The lens unit extends from the bottom portion towards the top portion and has a inverted-frustoconical-shaped light guide portion. A inverted-conical-shaped groove is defined in a topmost portion of the light guide portion. A reflective surface is positioned on an inner wall of the groove. A refractive surface is positioned on an outer surface of the light guide portion and intersects the reflective surface. The light emitting unit is positioned adjacent to the light incident surface.