By comparing the numbers. If the wavelengths are specified in different units (for example, meters and millimeters), you must convert them all to the same unit first.
There is no longest wavelength for photons. It can be arbitrarily long.
"radio waves" have longest wavelength..
-- longest wavelength -- lowest frequency
Red light has the longest wavelength.
The longest visible wavelength of light appears red. "Longest wavelength" is equivalent to 'lowest frequency'.
Red is the longest wavelength of visible light
Radio waves have the longest wavelength in the electromagnetic spectrum.
The color red has the longest wavelength of any color.
Red is the longest wavelength of visible light
Red light has the longest wavelength in the visible light spectrum.
The electromagnetic waves with the longest wavelength are called radio waves.
The longest wavelength / lowest frequency visible light is the red end of the spectrum. The shortest wavelength / highest frequency visible light is the violet end of the spectrum.