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A point source of light acts as an infinitely small beacon, casting rays uniformly in every direction. It's akin to imagining the sun shrunk down to an almost negligible size compared to its vast distances from the earth. While perfect point sources are purely theoretical, real-world approximations exist. For example, a distant star or the tiny glimmer of a firefly are similar to point sources because their size is so minuscule relative to the observer's distance.

The strength of illumination from a point source diminishes as you move away from it, following a specific principle known as the inverse-square law. This fundamental rule dictates that light intensity is inversely proportional to the square of the distance from the source, meaning that if you double the distance, the light's intensity drops to a quarter of its original strength.

In contrast to its point-sized counterpart, an extended source of light is substantial in size. These sources are akin to a chorus of voices, with each point on the surface contributing its melody of light. Take, for instance, the fluorescent lights above office desks or the warm glow spilling through a window; these are extended sources because they consist of numerous point sources combined.

The light from an extended source does not adhere strictly to the inverse-square law due to its complex distribution of individual light beams. Because of this, extended sources are excellent for achieving diffuse lighting, often resulting in softer shadows and a more uniform light spread in a room. They're the architects behind the even, gentle light we often encounter in daily life.

The inverse-square law is a pivotal concept in the realm of physics, particularly when discussing light and radiation. It states that as the distance from a point source increases, the intensity of light decreases in proportion to the square of the distance. Mathematically, if the distance from the source is doubled, the energy or light that reaches a given area is reduced to one-fourth. All point sources, from distant stars to a single candle flame, are subjected to this rule.

Understanding the inverse-square law is essential not only in physics but also in practical applications such as photography, where lighting is crucial, and telecommunications, where signal strength is paramount.

Various characteristics define the behavior of light sources, whether they are point sources or extended ones. These properties include intensity, which refers to the brightness of the light; color temperature, gauging the 'warmth' or 'coolness' of the light; and the directionality, which describes if the light travels in a focused beam or disperses widely.

Another critical attribute is the distribution of light. Point sources tend to exhibit radial symmetry, with light propagating spherically outward. Extended sources, conversely, provide a mosaic of light interactions, giving rise to different illuminating patterns. These properties govern a multitude of phenomena, from the simple casting of shadows to the intricate design of lighting systems in architecture and visual arts.