An assembly is provided for simulating the dilating and constricting of a pupil of an eye. The assembly includes a shell that is at least translucent to light and a dilation mechanism with a deformable member positionable to contact an inner surface of the shell. An actuator is provided in the dilation mechanism to move the deformable member toward and away from the inner surface, which causes the size of a contact area between the inner surface and a lip of the deformable member to vary over a preset range. The assembly includes a light source directing light onto the inner surface of the shell. The deformable member dynamically blocks light from reaching the inner surface, creating a pupil or dark hole. The light may be an ultraviolet light and the deformable member contacts a pattern or artwork on the inner surface including portions that glow in ultraviolet light.