A light-emitting element, comprises: a first active layer, generating a first light comprising a first dominant wavelength, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06eV and 0.1eV, and each of the first quantum-well and the second quantum-well is devoid of a barrier; and a second active layer on the first active layer, generating a second light comprising a second dominant wavelength; wherein a difference between the first dominant wavelength and the second dominant wavelength is 150nm to 220nm.