For many years, people have tried to understand the structure of vision and its role in the perception of the world by living organisms. Suffice it to say that, thanks to their visual organs, people receive most of their information about the world by optical means. Eyes of living organisms represent advanced light harvesting systems, developed through hundreds of millions of years of evolution. Some of their features are comparable or even superior to existing man-made photodetection devices. For example, rod photoreceptor cells of the retina, which are responsible for night vision, are small photodetectors, containing a photosensitive element (rhodopsin pigment) along with a “built-in” chemical power supply (adenosine triphosphate produced by mitochondria). Remarkably, these photodetectors have very high sensitivity, down to the single-photon level.