Parallel source and Distributed light source
a) Parallel source: this is to be noted that while point source is at an infinite distance then light rays are parallel and function as parallel source as demonstrated in figure 2, the parallel source is source b.
b) Distributed light source: this source models nearby sources as the long fluorescent light are modeled in category of distributed light source. Currently all light rays originate at a finite region in space. Demonstrated in Figure 2, the source c is a distributed light source.
Note: When a light is incident on an opaque surface, part of it is reflected and part of it is absorbed. The amount of incident light reflected through a surface depends on the category of material as shiny material reflects extreme of the incident light and dull surfaces absorb more of the incident light. Hence, from the reflected amount of light we can infer many properties of the surface beneath exposure.