a luminance current i l the drain of each transistor p i i ranging between 1 and n is connected to a column c i of the screen via a column selection circuit such as described in relation with fig2 all the column selection circuits are represented by a selection device 11 controlled by a column signal u03c6 c each column c l to c n is connected to the anode of a diode respectively d l to d n the cathodes of diodes d l to d n are connected to a current source 15 at a node c o current source 15 provides a so called observation current i ob selected to be small as compared to the minimum luminance current further connection node c ref is connected to the anode of a diode d ref identical to diodes d l to d n the cathode of diode d ref is connected at a node c oref to a current source 16 providing a current equal to observation current i ob nodes c ref and c o are connected to two inputs of an adjustment circuit cr which provides biasing voltage v pol as indicated previously the leds may even when run through by a same current exhibit across their terminals different voltage drops especially this voltage drop tends to increase when the leds age the present invention aims at adjusting voltage v pol to take these voltage variations into account and ensure that the chosen luminance current i l flows through all the selected columns v pol remaining as small as possible diodes d l to d n corresponding to the selected columns tend to be conductive however the.