A light emitting device includes a first light emitting unit and a second light emitting unit. The first light emitting unit includes a first composite layer, and the first composite layer includes an organic light emitting layer. The second light emitting unit is adjacent to the first light emitting unit, the second light emitting unit includes a second composite layer, and the second composite layer includes a quantum dot light emitting layer. A thickness of the first composite layer is different from a thickness of the second composite layer.