A plurality of LED-based lighting units is segmented into a plurality of LED-based lighting segments connected in series. Each lighting segment has a plurality of LED-based lighting units connected in series with at least a series-connection switch, and a bypass-connection switch is connected in parallel with the series of LED-based lighting units. The total number of LED-based lighting units can be determined by a maximum voltage level of an input voltage supply and the forward voltage of the LED-based lighting unit for achieving optimal efficiency. The number of lighting segments and the number of lighting units in each lighting segment are properly chosen based on the total number of the LED-based lighting units in such away that any number up to the total number of all the LED-based lighting units can be connected in series by respectively controlling the series-connection switch and the bypass-connection switch of each LED-based lighting segment.