One thing I've wondered about in this regard is the blink reflex. It's nicely tuned to protect our eyes from damage if we happen to glance towards the sun. It doesn't protect our eyes fast enough if we look at a brighter light source, as seems to have been demonstrated by people who were looking directly at the atomic bomb flashes over Hiroshima and Nagasaki.

Is the blink triggered by integrated brightness, or by surface brightness? If the former, then one can imagine that, out around Jupiter or Neptune, it would be possible to burn your retina without ever registering the danger: the solar disc would still have a surface brightness sufficient to damage your retina, but would not be bright enough overall to make you blink.

Grant Hutchison