A semiconductor laser structure is provided. A 4-wire assembly is used for replacing conventional incandescent light bulbs with fluorescent light bulbs in existing lighting fixtures recessed downlights, in particular. The drive assembly is connected to the crankshaft for rotation in unison therewith. The transfer function provides a substantially linear region at a center of a corresponding error window, including a first step size in the center of the error window and at least one other step size in a peripheral region of the error window that is larger than the first step size.