Why do we blink when a bright light suddenly shines into our eyes?

Answer: A protective reflex briefly closes the eyelids and reduces incoming light

The eyelids must reset the visual cells after every change in brightness — Closing the eyelids does not reset the visual cells. The visual system adjusts to brightness through changes in sensitivity; the blink briefly reduces exposure instead.

A burst of tears must wash bright light off the eye — Tears cannot wash light away: light enters the eye rather than sticking to its surface. Blinking does spread the tear film, but a sudden light-triggered blink is a reflexive response to the light.

A protective reflex briefly closes the eyelids and reduces incoming light ✓ — Bright light can trigger an automatic blink that briefly blocks incoming light. This is called the photic blink reflex. It is a protective response, not a guarantee that an intense light source cannot damage the eye.