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.
-- longest wavelength -- lowest frequency
There is no longest wavelength for photons. It can be arbitrarily long.
"radio waves" have longest wavelength..
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
The color red has the longest wavelength of any color.
Radio waves have the longest wavelength in the electromagnetic spectrum.
Red is the longest wavelength of visible light
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.
The longest wavelength photon I could find out about was in a maser (microwave version of a laser) which uses emission between two hyperfine levels of atomic hydrogen. This had a frequency of 1.4 GHz and a wavelength of 21cm.