The controversy over the observation of dark pixels by the DE-1 and Polar imagers has centered around the small-comet theory rather than an instrumental source to account for the dark pixels. To check for instrumental effects, we simulated the Polar VIS and UVI response to uniform illumination and calculated the rate of dark pixel clusters. The simulation includes the finite size and exponential amplitude of light pulses from the experiments' image intensifiers and the removal of contamination by penetrating radiation. The dark pixel cluster size distributions from the computer simulations reproduce the distributions observed in both of the Polar imagers. (The VIS distributions were produced independently from one day of raw data kindly provided by Frank and Sigwarth and from a world-wide-web catalog of atmospheric hole events prepared by Frank and Sigwarth from their own Polar data. These two sets of VIS distributions are in agreement with each other and with the computer simulations.) These instrumental effects fully explain the dark pixel clusters without the need for invoking a geophysical phenomena. ¿ 1998 American Geophysical Union