How can Power Factor be less than 1?

• If the there is time difference between voltage and current, that cause phase lag
• If the current - time and/or voltage - time waveforms are distorted from sinusoidal, called Total Harmonic Distortion.
• If any of the above two are not equal to 0 the power factor less than 1.

Where THD is Toatl Harmonic Distorstion and chi-theta is the Phase Lag of the fundamental harmonice