If we prepare a room with only one light source (eg a lightbulb) and dim the light more and more, eventually only tiny ``bits'' of light will be produced even in a long time period, eg one hour. More specifically, the dimness can be arranged so that a highly sensitive photographic film placed in that room will, after one hour, reveal only one or two tiny spots where it has been exposed to light. This means that, whatever light is, it arrives at the film in very tiny pieces. If we dim the bulb even more, the spots do not get dimmer, they simply become less frequent; any one spot remains just as bright as always, but may occur once a day, or once a year, instead of once an hour. It is as if light comes in little bundles and cannot be further reduced. For now, these pieces themselves may or may not best be thought of as little bullets (particles) or little waves. Let's use a neutral term: light bundles.