The invention concerns a motor vehicle's optical system for interior lighting where the optical system includes a screen and multiple light sources disposed in series where the light sources are configured to project a screen light beam and the optical system includes a light box between the light sources and the screen and where the light box includes multiple cavities where each light source is associated with a light box cavity and where each light source is activated independently. The invention also concerns a motor vehicle's interior lighting device that includes this kind of optical system.