Imagine strolling along a boardwalk at noon on a sunny day; how brightly the sunlight makes the sea sparkle! It's time for lunch and you enter a dimly lit restaurant. At first you can't see a thing—all seems black! But in a few minutes, you can see well enough to read the menu. You have a nice lunch and then emerge, blinking, back into the bright sunlight. Again, you can't see a thing—only an all-pervading white glare! But again, after a few minutes, your vision is restored and you can view the sailboats prancing among the waves. How is it that your eyes can make these remarkable adjustments and provide clear vision under a huge range of light conditions? More specifically, and among other such ...