Infrared was being used for all the convention workshops, plenary sessions and symposiums. After taking this workshop, I went into every event looking for the infrared panels, curious to see how they'd been placed. The panelists and moderator also did a great job of exploding the myths about infrared systems during their discussion. It uses invisible light to carry sound from a microphone to a receiver that you wear. It sort of piggybacks on the light.
Diodes also have intensity.
3-dimensional, like a cone, and is flooded into the room. There are different diode beam widths used by different companies. The quality of the signal at the receiver is dependent upon the intensity of the light. The receiver sees the invisible light and converts it to sound. Most studies of listening systems show infrared consistently at the top.