A light control signal generating circuit includes a photosensitive element, two transistors, and four resistances. A first resistance and the photosensitive element are connected in series between a power voltage terminal and a ground terminal. A base electrode of a first transistor is connected to a node between the first resistance and the photosensitive element, a collecting electrode is connected to the power voltage terminal through a second resistance, and an emitting electrode is connected to the ground terminal through a third resistance. A base electrode of a second transistor is connected to a node between the second resistance and the first transistor, a collecting electrode is connected to the power voltage terminal through a fourth resistance, and an emitting electrode is connected to the ground terminal through the third resistance. An output terminal is formed from a node between the fourth resistance and the second transistor.