- When we see an object we see reflected light from that object. Total reflected light the sum of contribution from all sources and reflected light from another object that falls on the object.
- So that the surface which not directly exposed to light may also visible if the nearby object illuminated.
- The simplest model for the light source is a point source. Rays from the source then follow radial diverging paths from the source position.
- Fig. Diverging ray paths from a point light source.
- This light source model the reasonable approximation for the source whose size small compared to the size of the object or maybe at sufficient distance so that we can see it as the point source. For example, the sun can take as the point source on earth.
- A nearby source such as the long fluorescent light more accurately modeled as a distributed light source.
- In this case, the illumination effects cannot approximate with point source because the area of the source not small compared to the size of an object.
- When light falls on the surface the part of the light reflected and part of the light absorbed. Amount of reflected and absorbed light depends on the property of the object surface. For example, shiny surface reflects more light while dull surface reflects less light.