Light and Dark Adaptation (Video Notes)

Vocabulary flashcards covering key terms and definitions from Week 4b notes on light and dark adaptation.

Light adaptation

The process by which the visual system reduces sensitivity to bright light, shifting the stimulus–response curve so more light is needed to evoke the same response; cones and rods adjust gain downward.

Dark adaptation

The process by which the visual system increases sensitivity in darkness, shifting the stimulus–response curve so less light is needed to detect a stimulus; rods and cones adjust gain upward.

Rods

Photoreceptors specialized for low-light (scotopic) vision; high sensitivity to light but low spatial resolution; dominate night vision.

Cones

Photoreceptors specialized for bright-light (photopic) vision; provide high acuity and color vision; operate best in bright conditions.

Photopic

Vision dominated by cones under bright illumination; high acuity and color perception; peak luminance efficiency around 555 nm.

Scotopic

Vision dominated by rods under low illumination; high sensitivity but poor color perception and acuity.

Mesopic

Intermediate luminance range where both rods and cones contribute to vision.

Iris

The pigmented ring that regulates pupil size; changes in light cause about an eightfold change in light entering the eye.

Rod-cone break

The transition point in dark adaptation when rod-mediated vision becomes dominant over cone-mediated vision.

Luminance

Perceived brightness of a surface, measured in candela per square meter (cd/m^2).

Lux

Unit of illuminance; one lumen per square meter.

Log scale

A scale where each unit represents a tenfold change in actual luminance, used to encode large intensity changes.

Log unit

An increment on a log10 scale; e.g., 0, 1, 2, 3, 4, 5 correspond to 1, 10, 100, 1000, 10000, 100000 times brightness.

Maximum cone sensitivity

The highest sensitivity of cones to light under photopic conditions, near 555 nm.

Maximum rod sensitivity

The highest sensitivity of rods to light under scotopic conditions, enabling night vision.

Relative luminous efficiency

The eye’s sensitivity to different wavelengths; peak photopic efficiency around 555 nm; rods peak near 498 nm.

Wavelength sensitivity (rods vs cones)

Rods peak around ~498 nm; cones have distinct peaks (blue ~437 nm; green ~533 nm; red ~564 nm).

Dark adaptation time (rods vs cones)

Rods take about 30 minutes to reach full dark adaptation; cones adapt quickly but to a lower maximum sensitivity.

Red light for night-reading

Using red light (around ≥630 nm) helps preserve night vision by favoring cones with lower rod sensitivity in low light.

555 nm peak (cone sensitivity)

Cones are most sensitive to green light near 555 nm, facilitating color and detail vision in daylight.