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The Space Interferometry Mission Planet Quest Light (SIM PQL) is a new concept for a space borne astrometric instrument. It will be located in a solar Earth-trailing orbit. SIM PQL utilized technology developed for the space interferometry mission planet quest (SIM PQ). The instrument consists of two Michelson stellar interferometers and a telescope. The first interferometer chops between the target star and a set of reference stars. The second interferometer monitors the attitude of the instrument in the direction of the target star. The telescope monitors the attitude of the instrument in the other two directions. SIM PQL will be capable of one micro-arc-second narrow angle astrometry, over a two-degree field of regard for magnitude 6 and brighter target stars. During the 5-year mission, SIM PQL would search 50 nearby stars for planets of mass down to one Earth mass, in the Habitable Zone, which have orbit periods of less than 3 years. SIM PQL will also perform global astrometry on a variety of astrophysics objects, reaching 6 micro-arc-seconds absolute position and parallax measurements. As a pointed instrument, SIM PQ will maintain its astrometric accuracy on fainter objects. This paper will describe the instrument, how it will do its astrometric measurements and the expected performance based on the current technology.