A calibration source IR assembly (100) for an IR detector (102) includes an IR focal plane (116). The calibration assembly (100) includes a rotatable spectral filter wheel (118) optically coupled to an IR focal plane (116) of the detector (102), the filter wheel (118) having a plurality of areas each of at least a minimum size. At least one area being a calibration area (120), the calibration area (120) including: a substrate (122) having a first side (124) facing the IR focal plane (116) and a second side (126) opposite from the first side (124); a light transmitting edge section (128) disposed between the first side (124) and the second side (126); and at least one light redirector (130) disposed at least partially within the substrate (122), the light redirector (130) structured and arranged to receive light from the edge (128) and to redirect the light out the first side (124). A light source (132) optically coupled to the edge section (128). An IR detector (102) including the improvement of such a calibration source (120) IR assembly (100) is also provided.