An illumination device includes a light source positioned on an illumination axis, a lens assembly having at least two biconvex lenses disposed on the illumination axis, and a reflector having a reflecting surface enclosing the lens assembly. The light source emits a first group of light beams which directly impinge of the lens assembly, and a second group of light beams which directly impinge on the reflector. The second group of light beams being reflected by the reflecting surface such that they surround the first group of light beams after being refracted by the lens assembly, without such second group of light beams impinging on the lens assembly.