I would like to know how large the contrast ratio is that the human
eye can discriminate in one view. As I know that this depends on the
state of adaption (mesopic, scotopic), the answer should state a
practical value for vision in the complete darkness of night and under
average daylight conditions. As I want to bring the value in relation
to photographic terms, it should be transfered into logarithmic
f/stops. Furthermore the answer must be based on reliable scientific
data with the source of the information stated.

Thank You !