What Is a Light Ray?

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A light ray is a basic element in geometrical optics. It is a hypothetical construct that, from any point in space, indicates the propagation of light. The concept that light travels in straight lines led to the development of the light ray concept.

In uniform mediums, light rays travel in a straight line. Light that is emitted from a small, localized source is represented by a collection of light rays that point radially outward from an idealized point source. A collection of parallel light rays, such as the light from a distant star and the light from a laser, is used to represent light flowing with uniform intensity through space.