LIGHTING CIRCUIT

A scanning light source 100 includes a semiconductor light source 110 and a motor 120, and scans output light of the semiconductor light source 110 in front of a lamp according to the movement of the motor 120. A constant current driver 220 supplies a driving current I to the semiconductor light source 110 according to a light source control signal S6. A light source control signal generator 210 generates the light source control signal S6 so as to obtain a light distribution pattern that corresponds to light distribution instruction data. A delay time measurement device 260 measures the delay time τ required for the transition of the on/off states of the semiconductor light source 110 from the change of the light source control signal S6.