A projection device, comprising a light emitting device and a first image forming assembly including a light relay, a TIR prism, a spatial light modulator, and a projection lens, wherein the light relay relays the light outputted by the light emitting device to the TIR prism, the TIR prism guides this light to the spatial light modulator, and guides the image light outputted by the spatial light modulator to the projection lens; wherein the light emitting device comprises: an excitation light source for generating an excitation light; a compensation light source for generating a compensation light having a spectral range different from a spectral range of the excitation light; a wavelength conversion device disposed on transmission paths of the excitation light and the compensation light, the wavelength conversion device including a segment having a second diffuser, a segment having a green wavelength conversion layer, and a segment having an orange wavelength conversion layer, arranged along a circumferential direction; wherein when the excitation light source and the compensation light source simultaneously illuminate different segments of the wavelength conversion device, the wavelength conversion device outputs a combined light of the compensation light and a converted light, wherein the compensation light has spectral overlap with the converted light; wherein the excitation light source is continuously turned on, wherein the compensation light source is turned on when the segment of the wavelength conversion device having the first wavelength conversion layer is located on a transmission path of the excitation light source, and is turned off when other segments are located on the transmission path of the excitation light source, wherein the first wavelength conversion layer converts the excitation light to a converted light that has spectral overlap with the compensation light. wherein the light relay relays the light outputted by the light emitting device to the TIR prism, the TIR prism guides this light to the spatial light modulator, and guides the image light outputted by the spatial light modulator to the projection lens; wherein the light emitting device comprises: an excitation light source for generating an excitation light; a compensation light source for generating a compensation light having a spectral range different from a spectral range of the excitation light; a wavelength conversion device disposed on transmission paths of the excitation light and the compensation light, the wavelength conversion device including a segment having a second diffuser, a segment having a green wavelength conversion layer, and a segment having an orange wavelength conversion layer, arranged along a circumferential direction; wherein when the excitation light source and the compensation light source simultaneously illuminate different segments of the wavelength conversion device, the wavelength conversion device outputs a combined light of the compensation light and a converted light, wherein the compensation light has spectral overlap with the converted light; wherein the excitation light source is continuously turned on, wherein the compensation light source is turned on when the segment of the wavelength conversion device having the first wavelength conversion layer is located on a transmission path of the excitation light source, and is turned off when other segments are located on the transmission path of the excitation light source, wherein the first wavelength conversion layer converts the excitation light to a converted light that has spectral overlap with the compensation light. an excitation light source for generating an excitation light; a compensation light source for generating a compensation light having a spectral range different from a spectral range of the excitation light; a wavelength conversion device disposed on transmission paths of the excitation light and the compensation light, the wavelength conversion device including a segment having a second diffuser, a segment having a green wavelength conversion layer, and a segment having an orange wavelength conversion layer, arranged along a circumferential direction; wherein when the excitation light source and the compensation light source simultaneously illuminate different segments of the wavelength conversion device, the wavelength conversion device outputs a combined light of the compensation light and a converted light, wherein the compensation light has spectral overlap with the converted light; wherein the excitation light source is continuously turned on, wherein the compensation light source is turned on when the segment of the wavelength conversion device having the first wavelength conversion layer is located on a transmission path of the excitation light source, and is turned off when other segments are located on the transmission path of the excitation light source, wherein the first wavelength conversion layer converts the excitation light to a converted light that has spectral overlap with the compensation light.