Light rays, by their nature, tend to propagate outward in straight lines in a phenomenon known as rectilinear propagation. This behavior is a consequence of light's ability to travel in a vacuum or through transparent media such as air or vacuum-like conditions.
The straight-line propagation of light rays can be understood using the concept of rays and rays of light. A ray of light is an imaginary line that represents the path along which light energy is traveling. It is often depicted as a straight line with an arrow indicating the direction of propagation.
When light is emitted from a point source, such as a candle or a bulb, it spreads out in all directions in a spherical pattern. This is because the light waves emitted from such sources originate from a single point, and they expand outward as the wavefronts progress. Each point on the wavefront emits new spherical wavelets, resulting in a spherical wavefront expanding outward.
The behavior of laser light is different because lasers produce highly focused and collimated beams of light. The light in a laser is emitted through a process called stimulated emission, where photons are emitted in-phase and have the same direction. This process produces a beam of light that is coherent and has a narrow divergence angle. Consequently, laser light can be approximated as a bundle of nearly parallel light rays, forming a straight-line beam.
In summary, light rays tend to propagate outward in straight lines due to the rectilinear propagation of light. Light waves emitted from sources like candles or bulbs spread out in a spherical pattern, while laser light, due to its coherence and collimation, can be approximated as straight-line rays.