When can I descent below the MDA if the approach light system does not have red terminating bars?
You can descend down to 100ft above TDZE if you have any ALS in sight. You need an ALS with red lights (ALSF I &amp; II) to go below that.

Red terminating bars/red side row bars help you find the threshold. Think of an ALS with red lights as being in the same category as Runway/lights/markings, Threashold/lights/markings, Touchdown Zone/lights/markings, VASI/PAPI, and REIL. Any other type of ALS (MALSR, MALSF, etc.) has the 100ft above TDZE restriction put on it when it is the only thing you can see.

@mins linked to a couple of helpful articles in the comments.