  The "radiation inner edge" of an accretion disk is defined as the inner
boundary of the region from which most of the luminosity emerges. Similarly,
the "reflection edge" is the smallest radius capable of producing a significant
X-ray reflection of the fluorescent iron line. For black hole accretion disks
with very sub-Eddington luminosities these and all other "inner edges" locate
at ISCO. Thus, in this case, one may rightly consider ISCO as the unique inner
edge of the black hole accretion disk. However, even for moderate luminosities,
there is no such unique inner edge as differently defined edges locate at
different places. Several of them are significantly closer to the black hole
than ISCO. The differences grow with the increasing luminosity. For nearly
Eddington luminosities, they are so huge that the notion of the inner edge
losses all practical significance.
