WHen you run an LED matrix like this each column if on only at the time you set it on in the hardware. If yo had a total of 8 columns then it is feasible that each of the columns is turned on in sequence (with its own proper data) and you get a net 1/8 duty cycle of active time for each of the columns. The trick with this is to do the switching from column to column at a rather quick rate. If you do it fast enough all of the columns will appear to stay on. This is an effect called visual persistance. Almost all multi-digit displays work this way from those on your microwave oven to the display on your LCD calculator.

This high speed scheme is sometimes called MULTIPLEXING.

Michael Karas