Infrared (IR) systems are similar to FM systems but use light waves to send signals from a transmitter to a receiver.
When using IR devices there needs to be an unblocked path between the speaker and the listener for the IR devices to work properly.
IR systems are a less popular choice than FM systems as they only work when there’s a clear path between the transmitter and the receiver.
They are also limited to indoor use as the signal is interrupted by sunlight when used outdoors during the day.
LoopMe by BHA has more information on Infrared systems and hearing augmentation solutions.