Air carrier First Officer reported seeing a lighted UAS off the right side of the aircraft during final approach into a Class B airport during night VMC conditions. The flight reported the UAS to the control tower and landed safely.

Narrative

On Date at approximately XA:20 local time in Seattle; I was Captain and in the role of Pilot Monitoring (PM) on flight from ZZZ to SEA. At the time; we were conducting an ILS 16R. At 300 ft AGL; we encountered what appeared to be a drone. The position of the drone was approximately 150 feet vertically above the aircraft and 150 to 200 feet laterally off the right side of the aircraft. At the time we were in VMC conditions with at least 10 SM visibility; light rain; and it was night. The First Officer (FO) was Pilot Flying (PF) and he disconnected the autopilot and auto throttle at FINKA intersection. As we approached 300 ft AGL we both spotted the drone at about the same time. The drone had a white light on the underside of it shining downward towards the ground which allowed both myself and the FO to see it and in that moment determine it was not a collision threat; although it was very close. It appeared to be stationary laterally and possibly climbing away from us. The drone had no other position lights other than the white light on the underside of it which made it impossible to see at night until we were underneath it. I elected to continue the landing as this seemed the safest course of action. After landing uneventfully; we reported the drone to Seattle ATCT. They gave us a number to call and I spoke to someone in the tower. We categorized it as a near miss for FAA/ATC purposes. I followed up with a phone call notification to dispatch and the Flight Operations Duty Officer. The FO conducted a post flight walk around and noted no evidence we contacted the drone and no aircraft damage present. Additionally; I wrote up the near miss with a drone in the aircraft logbook to ensure maintenance also conducted a visual inspection. A [local authority] met me at the gate to gather some information about the encounter. No recommendation other than including drones as a possible threat on every flight. The drone was located in Class B airspace where it should not have been; at night with no discernible position lights other than a downward facing spotlight.