Eye adaptation
Automatically adjusting a scene's exposure over a second or two to mimic how a real eye adjusts when you step from daylight into a dark room.
The eye has an enormous dynamic range, but only across time — the iris and retina need moments to adapt. Games fake it: the renderer measures the scene's average luminance (often from a downsampled histogram of the HDR framebuffer) and drifts the exposure toward it, so a bright exterior blows out briefly as you emerge from a cave, then settles.
Done well it sells the brightness of sunlight on a limited display; overdone, every doorway becomes a disorienting flash. It lives in the tone-mapping stage of an HDR pipeline, feeding the exposure value that maps scene light to displayable pixels. Auto-exposure is the same idea borrowed from camera terminology.