This is a version of the SP2 with a built-in dynamo and lamp.
The SP2D is based on the SP2 with only a few differences. The flywheel is 3" diameter, compared with 2" on the standard SP2. This is in order to provide a faster drive for the dynamo. The flywheel has a groove in the rim for the drive band, which drives a 1/2" pulley on the dynamo. The dynamo is mounted inside the base of the chimney and is wired up to a large red LED bulb in the top. There is no external electrical connection to the dynamo, so it cannot be used to feed anything other than the built-in LED (without modification).
As acquired, it appears to be unsteamed, although it was sold as used. I believe it was probably unused old stock. When first run on steam, it ran OK for a short while then suddenly stopped and jammed up solid. The crank pin had come loose and there was a slight burr on the edge of the cylinder. I don't know which was cause and which effect, or maybe coincidence, but both were easily fixed.