The exact electric motor that drove the rotating lamp appears to now be lost. It seems likely howerver that the motor in question was similar to this one for Callendar's apparatus, especially as the lamp's designer Charles Sherrington maintained a close relation with the Cambridge Scientific Instrument Company.  Sherrington describes the motor set-up of the lamp as follows: 

'The spindle of the revolving cylindrical screen was furnished with a step-pulley. Thence a rod ran to a step-pulley fixed on the spindle of an electro-motor. The speed of revolution of this motor was controlled by a set of coil-resistances, which served as a course adjustment, and by a fluid resistance in a trough 1 metre long, with a sliding electrode; this latter formed a fine adjustment.' (C.S. Sherrington, 'On Binocular Flicker and the Correlations of Activity of 'Corresponding' Retinal Points', Journal of Psychology 1 (1) (1904), p. 29)