The human eye could sense wavelength of light. The wavelength Is known as the main wavelength.and the peak wavelength is the wavelength of the spectrum. the wavelength corresponding to the energy of maximum value.For Blue ray as 470nm, green 520nm, yellow 570nm.due to the spectral distribution curve begins to rise just more fast. The wavelength remains sluggish when had a peak, the main wavelength integration two parts are mutually embedded to the main wavelength value ,so the main wavelength is longer than the peak wavelength;
With the example of the 589nm in yellow, orange light 605nm and red 630nm, we see that Those wavelength seems to start moving, smoothly and slowly beginning. over the peak after the more urgent the down, so the main wavelength is smaller than the peak wavelength . But anyway, the two difference is about 4nm.
To sum up:
*Wavelength of the main that Human eye could feel wavelength.
*Peak wavelength is the maximum wavelength at spectral energy distribution.
*The peak wavelength is short 5 nm than the length of the main wave.