Final answer:
Dark adaptation is the process by which the pupils dilate and the rods of the eyes become more active, allowing for improved vision in low-light conditions, such as entering a dark movie theater. This transition takes about 15 minutes for eyes to adjust from a well-lit to a dark environment.
Step-by-step explanation:
The phenomenon you're referring to, where you enter a darkened room like a movie theater and find it hard to see at first but gradually can see better, is known as dark adaptation. This occurs because the pupils in your eyes dilate to let in more light and the photoreceptors in your eyes adjust to the lower light levels. Specifically, the rods, which are photoreceptors responsible for vision in low light, become more active after a few minutes, enhancing your ability to see in the dark. The cones, which are responsible for color vision, are not as sensitive in low light and hence color perception is diminished.
During dark adaptation, the transition from cone-dominated to rod-dominated vision can take about 15 minutes. This is the time it typically takes for the pupil to fully open and the sensitivity of rods to reach their maximum, allowing you to see more clearly even with the faint light in the movie theater. This is also why after staring at a bright light or coming from a sunlit area, it takes some time for your eyes to adjust to darkness. Conversely, going back into a bright area will cause the pupils to constrict and the eyes will take a few minutes to adapt to the brighter setting.