The present invention provides an apparatus comprising a first out-coupling diffractive optical element and a second out-coupling diffractive optical element. Each of the first and second out-coupling diffractive optical elements comprises a first region having a first repeated diffraction spacing, d1, and a second region adjacent to the first region having a second repeated diffraction spacing, d2, different from the first spacing, d1. The first region of the first out-coupling diffractive optical element is superposed on and aligned with the second region of the second out-coupling diffractive optical element. The second region of the first out-coupling diffractive optical element is superposed on and aligned with the first region of the second out-coupling diffractive optical element.