Longest and shortest wavelength What is the longest and what is the shortest wavelength of light? How fast would a light-emitting object have to recede in order to shift the frequency of light to increase the wavelength from the shortest to the longest? (If there are limits)
Regarding visible light, the nominal range is usually given as 400 nm (violet) to 700 nm (red). For light of the former wavelength to get Doppler-shifted to the latter means a z value of (700–400)/400 = 0.75, corresponding to a recession of 152,000 km/s, just over half the speed of light.