The violet ray in the dispersion of light has the shortest wavelength in the visible spectrum, typically about 380–450 nm (nanometres). More precisely, in many textbooks and exam contexts you’ll often see it taken as roughly 400 nm for calculation and comparison purposes.

Quick Scoop

  • Visible light range: about 380–700 nm.
  • Violet light: about 380–450 nm , shortest wavelength among visible colors.
  • Red light: about 620–700 nm , longest wavelength among visible colors.
  • Because violet has the smallest wavelength, it is deviated the most by a prism, while red is deviated the least.

Why violet deviates more in a prism

When white light enters a prism, different wavelengths slow down by different amounts in the glass.

  • Shorter wavelengths (violet) experience a higher refractive index , so they slow more and bend more.
  • Longer wavelengths (red) experience a lower refractive index , so they bend less.

So, in dispersion of light through a prism, the violet ray at around 380–450 nm appears at the top of the spectrum (most deviation), and red at around 620–700 nm at the bottom (least deviation). TL;DR: For most practical physics questions, you can safely answer:

The wavelength of violet light in dispersion is approximately 400 nm , lying in the range 380–450 nm.