The DRI-55 with Collins Part Number 622-4160-01X is identical to the corresponding -00X except for the display dimming circuit. +5VDC applied to P-1 (main connector) Pin 24 gives max brightness (minimum dimming) on the -1X units and max dimming (minimum brightness) on the -00X. See image below:
Note the slope of the dimming curve, thus the term linear and non-linear dimming. Many corporate aircraft have "NAV LIGHT DIMMING". When the aircraft nav lights are turned on (night time operation) the annunicators and instrument lights go to minimum lighting or maximum dimming. Depending on whether the nav light system provides a high or low would determine which unit would be used. This is an engineering decision made when the aircraft was manufactured or modified.