There have been a large number of laboratory experiments on particle induced visual sensations which have resulted in a variety of visual phenomena that are similar in appearance to the so-called “light flashes” described by astronauts on Apollo missions 11 through 17 and Skylab 4. Unfortunately, no direct comparison of the laboratory and space observations have been made by observers who have experienced both. More than one physical mechanism has been shown to be involved in the laboratory phenomena and presumably in the space observations also. A number of models for particle induced visual phenomena are described and a quantitative estimate of their contribution to the space observations is attempted.