"H1" - The H1 represents the primary current with a Line facing direction. # Understanding Optical Power Meters (H1) Optical power meters are essential tools for measuring the power of optical signals in fiber optic communication systems. A current transformer with "H1" printed on one side is usually intending for that H1 to be on the side of the CT when the energy is being provided from, generally referred to as the high side, utility side, line side, or. What does solar display H1 mean? 1. This system is designed for presenting real-time data related to solar energy production. Indicates that the received optical power is normal.