Why can light be modeled as rays in geometrical optics?

In geometrical optics, light is modeled as rays—hypothetical constructs representing the direction of light propagation—because it provides a simple, effective way to trace the path of light through various media, reflections, and refractions.12

This model is valid as long as the physical dimensions of the objects and apertures light encounters are significantly larger than the wavelength of the light. Since visible light has relatively short wavelengths (400 to 700 nm), most everyday optical phenomena, such as the formation of images by lenses or mirrors, can be accurately described using this ray-based approximation.31

While the rules of geometrical optics can be derived from the classical electromagnetic-wave model, the ray model is preferred for its convenience in calculation and visualization. However, when the size of objects or apertures approaches the wavelength of light, the wave nature of light becomes significant, leading to phenomena like diffraction that the ray model cannot explain. In such cases, the more complex wave model must be used.32