A lamp circuit is disclosed, comprising a direct current (DC) power supplier (1) adapted to provide a supply voltage, a driving unit (2, 5) coupled to the DC power supplier (1) so as to receive the supply voltage, and a light-radiating module (3) coupled to the driving unit (2, 5). The lamp circuit is characterized in that the light-radiating module has a DC output side (33), and the driving unit (2, 5) generates a constant DC current that passes through the light-radiating module (3) such that a DC voltage to be supplied to a DC load (4) is built at the DC output side (33).