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How does diffraction demonstrate the wave properties of light?

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A horizontal gradient bar displays the visible light spectrum from violet to red, labeled with corresponding frequency in terahertz, wavelength in nanometers, and photon energy in electron volts. — light When white light is spread apart by a prism or a diffraction grating, the colours of the visible spectrum appear. The colours vary according to their wavelengths. Violet has the highest frequencies and shortest wavelengths, and red has the lowest frequencies and the longest wavelengths.

Diffraction provides clear evidence of the wave nature of light by demonstrating that light does not always travel in straight lines, as would be expected if it were composed solely of particles. Instead, when light encounters an obstacle or an aperture, it bends and spreads into the region of the geometrical shadow.123

This phenomenon occurs because of the superposition of waves. According to Huygens’s principle, every point on a wave front acts as a source of secondary spherical wavelets. When these wavelets are obstructed, the portions that pass through interfere with one another, creating a pattern of light and dark fringes.1

The effect is most pronounced when the size of the obstacle or aperture is comparable to the wavelength of the light. Because visible light has a very short wavelength, this bending is subtle and typically requires precise measurement to observe. Ultimately, diffraction confirms that light behaves as a wave, as these interference patterns are a fundamental characteristic of wave propagation.124