Plain English Meaning

The kind of seeing your eyes do at dusk or dawn, when it's too dim for full color vision but not yet dark enough that color disappears completely. Both sets of light-sensing cells in your eyes are working together.

Full Definition

Vision used in low-light conditions such as twilight or dim moonlight, in which both the cones (color and detail receptors) and the rods (low-light receptors) of the eye are active at the same time. It is the transition range between daytime cone-only vision and nighttime rod-dominant vision.

Context Anchor

Used in night flying and night vision discussions, especially when describing how a pilot sees during dusk, dawn, moonlight, or other low-light conditions.

Derivation

From the Greek 'mesos' meaning 'middle' and the Latin 'visio' meaning 'seeing.' The name reflects exactly what it is — the middle range of vision, sitting between bright-light vision and full night vision.