A light source assembly provides an illumination beam and the light
converging element is disposed on a transmission path of the illumination
beam. A light converging element has a top end and a bottom end opposite
to the top end. The light converging element is gradually reduced from
the bottom end to the top end. The top end is opposite to the light
source assembly and has a cavity. The illumination beam is incident into
the light converging element from the cavity and exits the light
converging element from the bottom end.