A light source apparatus (10; 11) comprising: a plurality of LED strings (310, 320, 330, 340) each connected to a respective transistor (TR1 to TR4) connected in a current mirror configuration; a power supply part providing power to a first terminal (311, 321, 331, 341) of each of the LED strings (310, 320, 330, 340); a current selection part selecting a current level of one of the LED strings (310, 320, 330, 340) to be a reference current level; and; and a current control part adjusting the levels of the currents (I1, I2, I3, I4) flowing through the LED strings (310, 320, 330, 340) to be substantially equal to the reference current level wherein the current control part comprises said respective transistors (TR1 to TR4) connected in said current mirror configuration; wherein the current selection part comprises diodes (D1-D4) respectively connected to the LED strings (310, 320, 330, 340), and each of the diodes (D1-D4) comprises an anode connected to the other diodes (D1-D4) and receiving a direct voltage and a cathode connected to a second terminal (312, 322, 332, 342) of one of the LED strings (310, 320, 330, 340); characterized in that the current control part comprises an adjusting circuit (TR5, R5-R8) connected with the current selection part, wherein the adjusting circuit (TR5, R5-R8) comprises an additional transistor connected to said respective transistors (TR1 to TR4) connected in said current mirror configuration; the current selection part is adapted to perform the current reference selection by detecting the voltages at the ends of each LED string (310, 320, 330, 340) opposite to the ends connected to the output (DOUT) of the power supply part by using the diodes (D1-D4) selectively connecting the collector of the transistor (TR1-TR4) having the lowest collector voltage (V1-V4) among said transistors (TR1 to TR4) in each LED string (310, 320, 330, 340) to the base of said additional transistor of the adjusting circuit (TR5, R5-R8), wherein the additional transistor of the adjusting circuit (TR5, R5-R8) is adapted to amplify the voltage across the base and the emitter of the transistors (TR1-TR4) and adapted to connect the base of each of the said transistors (TR1-TR4) to a pull-up source for providing the current leaked to the base of each of the transistors (TR1-TR4) through the pull-up source, wherein the current through the transistors (TR1-TR4) and through the LED strings (310, 320, 330, 340) follows the current of the transistor (TR1-TR4) having the lowest voltage at the collector. a plurality of LED strings (310, 320, 330, 340) each connected to a respective transistor (TR1 to TR4) connected in a current mirror configuration; a power supply part providing power to a first terminal (311, 321, 331, 341) of each of the LED strings (310, 320, 330, 340); a current selection part selecting a current level of one of the LED strings (310, 320, 330, 340) to be a reference current level; and; and a current control part adjusting the levels of the currents (I1, I2, I3, I4) flowing through the LED strings (310, 320, 330, 340) to be substantially equal to the reference current level wherein the current control part comprises said respective transistors (TR1 to TR4) connected in said current mirror configuration; wherein the current selection part comprises diodes (D1-D4) respectively connected to the LED strings (310, 320, 330, 340), and each of the diodes (D1-D4) comprises an anode connected to the other diodes (D1-D4) and receiving a direct voltage and a cathode connected to a second terminal (312, 322, 332, 342) of one of the LED strings (310, 320, 330, 340); characterized in that the current control part comprises an adjusting circuit (TR5, R5-R8) connected with the current selection part, wherein the adjusting circuit (TR5, R5-R8) comprises an additional transistor connected to said respective transistors (TR1 to TR4) connected in said current mirror configuration; the current selection part is adapted to perform the current reference selection by detecting the voltages at the ends of each LED string (310, 320, 330, 340) opposite to the ends connected to the output (DOUT) of the power supply part by using the diodes (D1-D4) selectively connecting the collector of the transistor (TR1-TR4) having the lowest collector voltage (V1-V4) among said transistors (TR1 to TR4) in each LED string (310, 320, 330, 340) to the base of said additional transistor of the adjusting circuit (TR5, R5-R8), wherein the additional transistor of the adjusting circuit (TR5, R5-R8) is adapted to amplify the voltage across the base and the emitter of the transistors (TR1-TR4) and adapted to connect the base of each of the said transistors (TR1-TR4) to a pull-up source for providing the current leaked to the base of each of the transistors (TR1-TR4) through the pull-up source, wherein the current through the transistors (TR1-TR4) and through the LED strings (310, 320, 330, 340) follows the current of the transistor (TR1-TR4) having the lowest voltage at the collector.