Infrared is an invisible light with directivity. The sensitivity of a
receiver is at its best when it is aimed directly towards a radiator.
The axis of maximum sensitivity is tilted upwards at an angle 45
degrees(Figure 1). Rotating the receiver will decrease the sensitivity. For rotations of less than 45 degrees this effect is not large, but for larger rotations the sensitivity will decrease rapidly.

Since infrared radiation can reach a receiver directly and/or via
diffused reflections(Figure 2), it is important to take this into
account when considering the positioning of the transmiters.
Though it is best if receivers pick up direct path infrared radiation,
reflections improve the signal reception and should therefore
not be minimised. Transmitters should be positioned high enough not to be blocked by people in the hall(Figure 3).