Overfill light illuminating the area outside the active array can create artifacts from the mechanical features and other surfaces that surround the active array. These artifacts may be visible in the projected image. The illumination optical system should be designed to minimize light flux incident outside the active array and on the window aperture. Depending on the particular system’s optical architecture and assembly tolerances, this amount of overfill light on the area outside of the active array may still cause artifacts to be visible. Illumination light and overfill can also induce undesirable thermal conditions on the DMD, especially if illumination light impinges directly on the DMD window aperture or near the edge of the DMD window. Refer to Section 6.4 for a specification on this maximum allowable heat load due to illumination overfill.