A light-emitting device includes a power module, a first light-emitting module, a second light-emitting module, a third light-emitting module, and a control module. The power module is configured to rectify an AC voltage for providing a periodic driving voltage. The first, second, third light-emitting modules are connected in series. The control module is configured to make the first, second, third light-emitting modules being driven by the driving voltage in response to different driving stages in a cycle period of a driving voltage. An average-diode-junction-area of the first light-emitting module is different from an average-diode-junction-area of the second light-emitting module or an average-diode-junction-area of the third light-emitting module.