Important points about Types of light resources - illumination model
Note: While we see an opaque non-luminous object, we notice reflected light by one surface of the object. The whole reflected light is the sum of all contribution from light sources and the other reflecting surfaces in the scene. Hence a surfaces which is not directly exposed to a light resource may yet be visible if nearby objects are illuminated.
By figure of 1 we can conclude about the expression i.e. specified below holds good in real life conditions
Light viewed from opaque non-luminous surface = Light from sources + Light from Other Surfaces
Because light sources are fairly dominant that is needed to establish realism in any graphic scene. Moreover, there are a variety of light sources, thus we require classifying them.
Sources of Light can be categorized as:
a) Point source
b) Parallel Source
c) Distributed Source