A backlight assembly comprises an optical plate that has a fixing portion and a receiving member that has a combination portion combined with the fixing portion. First and second wing members are pivotally mounted to the main body, whereby the wing members include respective cam surfaces that deflect the inner surface of the locking insert toward the threaded shaft. In one application, the apparatus can be used to extract spectral lines of an analyte from radiation scattered from a sample. All tuners receive the same signal and no signal degradation is caused when connecting multiple tuners.