visual threshold

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vis·u·al thresh·old

, threshold of visual sensation
the minimal light intensity evoking a visual sensation.
References in periodicals archive ?
The scotopic visual threshold of juvenile Pacific bluefin tuna for optomotor reactions was at least 40-fold inferior to the threshold of four marine teleosts: grouper (Epinephelus septemfasciatus), purplish amberjack (Seriola dumerili), ocellate puffer (Takifugu rubripes), and red sea bream (Pagrus major) (Ishibashi et al.
Since the optically imperfect human eye scatters a lot of light, improved blackness generation by the normal retina would not be desirable at night because it would require elevating the visual threshold to eliminate the fluctuating background generated by neural dark current.
That part of the curve above the visual threshold almost exactly matches the contrast curve of a somewhat smaller, unobstructed instrument