A person walks from a brightly lit street into a dark cinema. Explain how the eye responds to this change in light intensity, and describe how the structure of the retina allows the person to see in the dim light inside the cinema.

The pupil dilates when light intensity falls, because the circular muscles of the iris relax and the radial muscles contract, increasing pupil size and allowing more light to enter the eye.
The retina contains rod cells that are highly sensitive to low light levels, so they become the main photoreceptors in dim conditions.
Rod cells are not colour‑sensitive; they only detect light intensity, which is sufficient for vision in the dark.
The large number of rods in the peripheral retina gives a wide field of view and good sensitivity to movement in low light.
Thus the eye adapts by widening the pupil and relying on rod cells, enabling the person to see in the cinema's dim light.