The invention discloses an optical assembly comprising a plurality of optical components that are concentric to one another, each optical component having a partially reflective and partially transmissive interface with an oblique angle of incidence, and the reflectivity of the interface increasing with distance from a common center; a transitional optical component is provided between the light source and the first optical component in order to direct lights from a light source to the partially reflective and partially transmissive interface of the first optical component. By assembling the plurality of optical components, a much thinner lighting device (100) can be achieved.