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Sunny days and dark nights: the human eye can adapt to large differences in luminance, but it is also sensitive to glare.
Anyone who has ever looked directly into a brightly illuminated flashlight in the dark can immediately relate. The eye is capable, for its own protection, of adapting to different lighting conditions — the so-called light-dark adaptation. When brightness changes, the eye requires time to adjust. Immediate visual performance is determined by the current state of adaptation.

Adjustment from dark to light takes only seconds. Conversely, it can take more than 30 minutes for the eye to adapt from light to dark, for example when leaving a well-lit room into darkness at night.
Cones in the retina register daylight; there are three types of cones for the primary colors blue, red and green. Night vision, by contrast, is handled by the much more light-sensitive rods, which can only distinguish gradations of brightness or shades of gray.

Adaptation of the visual system to changing light intensities occurs in several stages. In the first stage the pupil reflexively constricts or dilates. With an open iris up to 80 times more light can enter the eye than with an almost closed aperture. In the second stage, depending on the lighting conditions, rods or cones are preferentially activated. Rods only enable black-and-white vision; they are the low-light receptors of the eye and are activated at dusk (scotopic vision). In bright light, cones are predominantly active and enable color vision (photopic vision).

If an eye adapted to darkness is exposed to a light source (other than red light), night vision is lost within seconds because the rods react immediately to the light source.
Red light has a spectral curve outside the sensitivity range of the rods (see the blue “night vision” curve in Figure 1). It does not affect the adaptation process; night vision therefore remains intact for an extended period.
Other colors, with the exception of amber, lie within the reception range of the rods and thus influence the adaptation process to a greater or lesser extent.