The minimum difference in wavelength that the human eye can distinguish between, known as the just noticeable difference (JND) or the difference threshold, depends on various factors, including the specific wavelengths involved and individual differences in perception. However, in general, the average human eye can discern a JND of approximately 1 nanometer (nm) in the visible light spectrum.
It's important to note that this value is an approximation and can vary from person to person. Factors such as lighting conditions, background contrast, and individual variations in color perception can affect the ability to distinguish small differences in wavelength. Additionally, the JND tends to increase as the wavelengths move towards the extremes of the visible spectrum (i.e., violet and red regions).
Overall, a JND of around 1 nm is often considered a reasonable estimate for the minimum difference in wavelength that the human eye can perceive under typical conditions.