[klondike98]

Check out the information in this web posting by Chuck Schwark.  Your lamp question is answered by Chuck: "There were two types of Shadow Meters; an early model used prior to 1935 or so, and a later type used up through 1938 models. The early types meters used a screw base lamp and the later used a bayonet base lamp. The screw type can be replaced with a type 46 lamp and the bayonet type replaced by a type 44. Both are rated at 6.3 volts drawing 250 milliamps."