log mel energies

I want to convert mel spectogram to log mel energies what I used is

y, sr = librosa.load(filename, sr=16000)
mel_spectrogram = librosa.feature.melspectrogram(
    y=y, sr=sr, n_mels=128, n_fft=1024, hop_length=512, power=2)
log_mel_spectrogram = librosa.power_to_db(mel_spectrogram)

I thought this converts to mel energies but I found this line of code

log_mel_spectrogram = 20.0 / power * np.log10(np.maximum(mel_spectrogram, sys.float_info.epsilon))

My question is what is the difference between log-mel spectrograms and log mel energies, which line of code to use