The time taken to read out the TV camera of the IPCS, and update the Detector Memory System is referred to as the TV frame-time. Clearly, at high light levels, when photons arrive at the same (x,y) coordinate within one frame-time, a system such as the IPCS will suffer from coincidence losses. The result is that the detector becomes non-linear, and the way in which this happens is discussed in detail by Jenkins (Monthly Notices of the Royal Astronomical Society, vol 226, p341, 1987). The only solution is to keep the light level below the point at which coincidence losses become important. Rough estimates of acceptable light levels are as follows:
For the CCD-IPCS, coincidence losses of around 10% are anticipated at count rates of about 1 photon per pixel per second from continuum sources in lowest resolution mode with full format.