The phenomenon you're referring to is known as wave interference. When light waves encounter obstacles or pass through narrow openings, they can exhibit diffraction and interference effects, leading to the observed patterns of light and dark regions.
Light waves, like other waves, can undergo diffraction, which is the bending or spreading out of waves when they encounter an obstacle or pass through a narrow aperture. Diffraction causes light waves to spread out and interact with each other, leading to interference patterns.
Interference occurs when two or more light waves overlap and interact with each other. Depending on the relative phases of the waves (the alignment of their peaks and troughs), they can reinforce each other (constructive interference) or cancel each other out (destructive interference). This interference creates patterns of alternating light and dark regions.
The reason light waves exhibit interference patterns is due to their wave nature. Light is an electromagnetic wave, and it follows the principles of wave propagation. When light encounters obstacles or narrow openings comparable to its wavelength, it undergoes diffraction and interference based on the wavefronts and their interactions.
It's important to note that interference patterns can only be observed when dealing with waves, whether it's light waves, water waves, or other types of waves. In the case of light, interference patterns can be observed in experiments such as the double-slit experiment, where light passes through two closely spaced slits and produces an interference pattern on a screen.
In summary, the patterns of light waves observed are a result of the wave nature of light and the phenomena of diffraction and interference, which cause the waves to spread out and interact with each other, resulting in the observed patterns of light and dark regions.