A current driver circuit structured to drive a plurality of semiconductor light sources (102_1; ... ; 102_N), the current driver circuit comprising: a plurality of current sources (310_1; ... ; 310_N) each structured to allow an on/off state thereof to be controlled independently according to a PWM signal of a plurality of PWM signals (S PWM1 ; ...; S PWMN ), and to each be coupled to a corresponding semiconductor light source (102_1; ...; 102_N) in series; an interface circuit structured to receive, from an external processor a plurality of control data (D 1 ; ...; D N ) that indicates an on/off duty cycle for the plurality of current sources (310_1; ... ; 310_N); and a dimming pulse generator structured to generate the plurality of PWM signals (S PWM1 ; ...; S PWMN ) for the plurality of current sources (310_1; ... ; 310_N), characterized in that, the interface circuit is structured to receive the plurality of control data at a first time interval T1; the dimming pulse generator is structured to gradually change, in a gradual-change mode of the dimming pulse generator , at a second time interval T 2 that is shorter than the first time interval T 1 , with T 1 being an integer multiple of T 2 , a duty cycle of each of the plurality of PWM signals (S PWM1 ; ...; S PWMN ) from a value indicated by the corresponding control data (D 1 ; ...; D N ) before updating to a value indicated by the corresponding control data (D 1 ; ...; D N ) after updating, wherein, with T 1 / T 2 = a, and with the difference in the value between the control data (D 1 ; ...; D N ) after updating and the control data (D 1 ; ...; D N ) before updating as ΔX, the dimming pulse generator changes the duty cycle linearly at the second time interval T 2 in a stepwise manner in steps of ΔY = ΔX/a. a plurality of current sources (310_1; ... ; 310_N) each structured to allow an on/off state thereof to be controlled independently according to a PWM signal of a plurality of PWM signals (S PWM1 ; ...; S PWMN ), and to each be coupled to a corresponding semiconductor light source (102_1; ...; 102_N) in series; an interface circuit structured to receive, from an external processor a plurality of control data (D 1 ; ...; D N ) that indicates an on/off duty cycle for the plurality of current sources (310_1; ... ; 310_N); and a dimming pulse generator structured to generate the plurality of PWM signals (S PWM1 ; ...; S PWMN ) for the plurality of current sources (310_1; ... ; 310_N), characterized in that, the interface circuit is structured to receive the plurality of control data at a first time interval T1; the dimming pulse generator is structured to gradually change, in a gradual-change mode of the dimming pulse generator , at a second time interval T 2 that is shorter than the first time interval T 1 , with T 1 being an integer multiple of T 2 , a duty cycle of each of the plurality of PWM signals (S PWM1 ; ...; S PWMN ) from a value indicated by the corresponding control data (D 1 ; ...; D N ) before updating to a value indicated by the corresponding control data (D 1 ; ...; D N ) after updating, wherein, with T 1 / T 2 = a, and with the difference in the value between the control data (D 1 ; ...; D N ) after updating and the control data (D 1 ; ...; D N ) before updating as ΔX, the dimming pulse generator changes the duty cycle linearly at the second time interval T 2 in a stepwise manner in steps of ΔY = ΔX/a. <EOS>