A light emitting device includes: a plurality of light emitting modules each provided with a circuit board, and first to n-th light source groups disposed on the circuit board, n being an integer greater than two, wherein the first to n-th light source groups each include at least one light emitting diode (LED); a driving module supplying driving power to the plurality of light emitting modules, and determine a number of light source groups operating in each of the plurality of light emitting modules based on a level of the driving power; and a module connection unit connecting first to n-th light source groups provided in one of the plurality of light emitting modules and first to n-th light source groups provided in another light emitting module in parallel in a detachable manner, respectively.