The invention provides a collimator comprising a first collimator face, a second collimator face, and a stack region. The stack region comprises a first layer having a first prismatically shaped top face with a plurality of 1D arranged first prisms having first prism axes, and a second layer having a second prismatically shaped top face with a plurality of 1D arranged second prisms having second prism axes. The first and second prism axes are in a crossed configuration. In a direction from the first collimator face to the second collimator face, the index of refraction of material upstream of the first prismatically shaped top face is larger than that of material downstream of the first prismatically shaped top face, and the index of refraction of material upstream of the second prismatically shaped top face is larger than that of material downstream of the second prismatically shaped top face.