disclosed is a lighting optical system , including : a lighting optical system , comprising , a light separating means for separating incident light into three colored lights according to wavelength bands , and progressing the three separate colored lights for the same amount of distance from a light source of the incident light through different optical paths , and emitting the three separate colored lights to a first , a second and a third lcd , a first , a second and a third lcd for respectively receiving the three colored lights from the light separating means , and forming images therefrom ; and a light combining means for synthesizing the three colored lights emitted from the first , second and third lcd , and outputting the synthesized light outside .