A device for measuring the output of an LED with a detector under different distance conditions without requiring the movement of either the LED or the detector. An exemplary embodiment of the present invention implements the testing conditions specified in CIE 127 allowing the determination of Averaged LED Intensity at the specified distances of 100 mm and 316 mm while keeping the physical distance between the LED and the detector fixed at the shorter distance of 100 mm. The exemplary embodiment comprises an optical element that can be selectively inserted into the optical path between the LED and the detector to make the separation appear to be the longer of the two distances. The optical element comprises a lens assembly and a detector aperture that creates a virtual image of the detector aperture at the longer of the two distances. The detector aperture is dimensioned so that the virtual image of the detector aperture has the area required by the standard.