It is a problem to provide a light-emitting device capable of obtaining a constant
brightness without being affected by deterioration in an organic light-emitting
layer or temperature change, and of making desired color display. The lowering
in OLED brightness due to deterioration is reduced by causing the OLED to emit
light while keeping constant the current flowing through the OLED instead of causing
the OLED to emit light while keeping constant the OLED drive voltage. Namely, OLED
brightness is controlled not by voltage but by current thereby preventing against
the change in OLED brightness due to deterioration of OLED. Specifically, the drain
current Id of a transistor for supplying a current to the OLED is controlled in
a signal line drive circuit thereby keeping constant the drain current Id without
relying upon the value of a load resistance.
