To find the energy of a wave, the energy is found using E=hf where h is Plank's constant and f is the frequency of the wave.
Relating frequency and wavelength we can use the equation v = (f)(lambda)
If the wavelength is large then the frequency is small. If the wavelength is small then the frequency is large. The larger the frequency a wave has then the more energy it has.
Since this is a low energy wave, that means it has a low frequency and a large wavelength.