Wireless Sensor and Actuator Networks for Lighting Energy ...

(2) Subtle and invisible shadows may exist on the testing desktop. The shadows
could be introduced by objects on the desktop such as the computer chassis,
monitor, decorations and laptop (if the subjects brought their own laptop to
work).
(3) Reflection of light from the walls or glossy surfaces of objects on the desktop
may be picked up by the nearby sensors. In the testing office, one side of the
desktop was attached to the wall where there was a poster with a glossy surface
and a picture frame with a glass cover. Both of them could reflect light and cause
the variations of sensor readings.
Although the above three factors could very well be prevented by carefully
designing the testing environment, no ordinary office can avoid any of them in reality.
Therefore, the testing results still provide valuable information for further improvement
to accommodate the impact of fused values deviating from the perceived illuminance
due to customized sensor locations.
Allowing the subjects to select the photosensor locations may compromise the
accuracy of the fused values estimating the lighting perceived by the occupants. The
fusion algorithm extracts a pertinent representation of the illuminance sensed by each
individual sensor; in other words, there is no way for the algorithm itself to figure out
the illuminance of the target surface if all the sensor readings deviate from that in the
first place. The most important implication of the testing results is that instead of the
absolute illuminance, it would be more efficient and realistic to identify occupants’
preferences and control the lights using the fused sensor readings when designing the
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