text: low beam car lights place the bulb out of focus of a revoluted parabolic, while high beams place the bulb rght in the focus, so high beams are longer and brighter...\n\nhow do you think a parabolic antenna works (like DirecTV, or SKY)? signals are emitted from the focus of an antenna and reflexed on the dish,  then is difused, unless this waves find another antenna which receives and re-concentrate signal into the focus, then a decoder does its work and let you watch the Superbowl or Smallville...\n\nAlso, circles are conics... have you played witha hula-hula?\n\nhave you noticed conics are all around you?\n\nHope I help.