b for a cell to which voltage b is applied and that should not change its state furthermore additional extreme cases c and d are shown corresponding to a data voltage the sign of which is inverted outside of the control window with respect to the one that generates the voltages shown in fig2 it is clear that in a general case diagrams intermediate between a and c in the white case and between b and d in the black case are obtained for the transmission but transmissions intermediate between a and d will never be obtained in a time scale longer than the one shown but small with respect to the refresh time the bistable cell relaxes to one or the other of the two extreme stable states as a result thereof the variability of the light transmitted within the refresh interval between the various cases corresponding to black or to white is much lower than the span appearing in fig3 and can be considered as effectively acceptable more precisely as concerns the selection voltage amplitudes of 65 volts for writing and 26 volts for erasing and as concerns the data voltage amplitudes of 13 5 volts have been used a row addressing time of 60 microseconds has been achieved an advantage of the first exemplary embodiment when the erasure results into a black state is the reduced perception of light flashes by the observers at each selection operation a first drawback is the above mentioned relatively noticeable effect of the data voltages outside of the control window on the transmission of the cell at the end of the selection pulses it can be nearly eliminated by use of crosstalk compensated data voltages and by changes in the level of the selection voltage.