level the duty cycle is changed for the two leds with an alternating current signal having a positive mean value as shown by plot 40 a the led 4 b is brighter as the positive duty cycle period is longer than the negative duty cycle period whereas the led 4 a is dimmer with an alternating current signal having a negative mean value as shown by plot 40 c the led 4 a is brighter as the negative duty cycle period is longer than the positive duty cycle period whereas the led 4 b is dimmer for a signal with zero offset the brightness is the same plot 40 b fig5 shows the current flowing through leds 4 a and 4 b when a drive current for the bright led 4 a plot 40 c is used in a further embodiment three different leds can be driven as shown in fig6 in the example of fig6 in order to achieve one more degree of multiplexing an extra conductor path is added using an extra cut 6 a in the ito coating this creates three ito regions 7 a 7 b 7 c the drive circuitry comprises two current sources 8 and 60 and an extra set of connector wires 9 a the first led 4 a i e the one with the same polarity as the first led 4 a in fig3 is connected between the first and second regions 7 a 7 b with the cathode connected to the first region 7 a and the anode connected to the second region.