A beam of light is a narrow stream of light particles, known as photons, that travel in a straight line. This phenomenon occurs when light is emitted from a source, such as the Sun or a light bulb, and can be observed as a focused line of brightness. Beams of light can be seen in various situations, such as when sunlight filters through trees or when a flashlight is pointed in a dark room. They can also be affected by objects in their path, leading to effects like shadows or reflections, which are important in understanding concepts like optics.