It arises in physical devises when a charged particle moves through a potential gradient without collisions and with random starting time. Current flow in detector is not continuous, electrons have discrete charge. Photon aspect of light is important. Assume an ideal detector. We reduce the intensity of light.
Probability is one.
Out of all the N R rooms in the building, we are in room 411. Entropy and communication. S is called the entropy or average information and is expressed in bits. Similar in form to the entropy used in thermodynamics. Information content in a picture .