A system for time-sequential LED-string excitation includes a controller coupled to at least two LED strings and arranged to sequentially excite the strings—preferably by pulse-width modulating their respective currents—such that each string conducts a desired current and/or provides a desired light intensity. Individual string currents and/or light intensities are provided to the controller as feedback signals. The controller preferably pulse-width modulates each string such that it conducts a current which approximates the performance that would be provided if the string were made to continuously conduct an ‘optimal’ current. A voltage converter may be included to provide the supply voltage connected to the top of each LED string, and to adjust the supply voltage as needed to ensure that each string conducts a desired current.