In a room with a smooth ceiling, detectors should be spaced horizontally between
30 and 60 feet (9.1 to 18.3m). One-half that spacing between the beam
and the sidewall may be used as a guide. See Figure 1. The beam detector
can be mounted with the transmitter/receiver on one wall and the reflector
on the opposite wall, or both suspended from the ceiling, or any wall/ceiling
combination. In the case of the ceiling mount, the distance from the end walls
should not exceed one-quarter of the selected spacing (7.5 ft. [2.3m] maximum
if the spacing is 30 ft. [9.1m] ). See Figure 2.