How does diffraction produce coloured patterns around obstacles and openings?

Diffraction is the phenomenon where light waves spread as they encounter the edges of an obstacle or pass through an opening, a process fundamentally rooted in the wave nature of light.12

When light is obstructed, the portions of the wavefront that are not blocked act as secondary sources of spherical wavelets, as described by Huygens’s principle. As these wavelets propagate into the region beyond the obstacle, they undergo interference, where they may reinforce each other (constructive interference) or cancel each other out (destructive interference).321

This interference produces patterns of light and dark bands. Because the amount of bending—and thus the resulting interference pattern—is proportional to the wavelength of the light, white light (which contains multiple wavelengths) is dispersed into a sequence of spectral colours. In regular arrays of obstacles or openings, such as a diffraction grating, these waves interact to reinforce specific colours at different angles, creating intense, observable spectral patterns.143