Figure 2-15 shows the first scan line dim issue. In ultra-low illumination the first line of each stackable led matrix will darker than other lines. The voltage of un-conducted line is forced to float with the turn-on OUTx. Since the uncertainly starting voltage of first line, whose voltage can be higher or lower than other lines, causing the first line of every multiplexing is darker comparing to other lines.

Figure 2-15 First Line Dim Issue