The human eye has a biological control system that varies the pupil diameter to maintain constant light. As the light intensity increases, the optical nerve sends a signal to the brain, which commands internal eye muscles to decrease the pupil's eye diameter. When the light intensity decreases, the pupil diameter increases.
a) Draw a functional block diagram of the light-pupil system indicating the input, output, and intermediate signals; the sensor; the controller; and the actuator.
b) Under normal conditions the incident light will be larger than the pupil, as shown in Figure(a). If the incident light is smaller than the diameter of the pupil as shown in Figure(b), the feedback path is broken (Bechhoefer, 2005). Modify your block diagram from Part a. to show where the loop is broken. What will happen if the narrow beam of light varies in intensity, say in a sinusoidal fashion?
c) It has been found (Bechhoefer, 2005) that it takes the pupil about 300 milliseconds to react to a change in the incident light. If light shines off center to the retina as shown in Figure(c), describe the response of the pupil with delay present and then without delay present.
