What is defined as a group of rays divergent from a single point on a light source?

The correct understanding of a "pencil of light" refers to a collection of light rays that originate from a single point and spread out in different directions. This concept is often used in optics to describe how light can be perceived as emanating from a source, such as a lamp or a laser. A pencil of light has a specific geometric shape, typically cylindrical or conical, depending on how the rays diverge.

This term is particularly important in various optical applications, including photography, laser technologies, and optical systems design, where controlling the direction and distribution of light is essential. By defining a pencil of light, one can better understand the behavior of light within different media and the effects caused by various optical devices.

In contrast, while a beam of light might also represent a collection of rays, it usually implies more directed light, such as a flashlight beam, rather than the more generalized divergence of rays from a single point. Optical fibers involve the guided transmission of light through fibers rather than diverging rays from a point, and light rays alone is a general term that does not capture the specific reference to divergence from a single source.