A radiation sensor includes a radiation receiver positioned in a focal plane of the final element of the projection system; a transmissive plate supporting the radiation receiver at a side facing the projection system; a quantum conversion layer to absorb light at the first wavelength incident on the transmissive plate and reradiate light at a second wavelength; a fiber optics block with a plurality of optical fibers; and a radiation detector. In the radiation sensor, the plurality of optical fibers guide light is reradiated by the quantum conversion layer towards the radiation detector. The radiation sensor can be used as a substrate-level sensor in a lithographic apparatus.