Wireless Sensor and Actuator Networks for Lighting Energy ...

(a)
(b)
Figure 8-10 Sensor placement of subject No. 10.
Overall, the fused values matched the meter readings, and hence the lighting
perceived by the subjects, in only 20% of the cases. In 60% of the cases, the fused
values were constantly lower than the meter readings, and the fused readings were
constantly higher than the meter readings in the other 20% of the cases. The plots of
sensor readings and the pictures of sensor locations for all of the participants are listed
in Appendix B.1. Although in most cases it is not obvious to the participants and the
investigator why each individual sensor measurement deviated from the meter
measurement, several reasonable conjectures can be made as follows:
(1) The light on the desktop might not be uniformly distributed. This could be
caused by the design of the luminaires and their layout in a room. In the testing
office, the desk was located at the place where approximately half of its surface
was directly beneath one of the four troffers while the rest of the surface was not.
As the workplane level illuminance model in Figure 6-2 suggests, the linear
combination of four such models is not likely to produce evenly distributed
lighting on the desktop.
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