Wireless Sensor and Actuator Networks for Lighting Energy ...

The physical limitations of light outputs from the luminaires are also posed as
constraints to the linear programming problem. As a result, if the number of constraints
(present occupants) is close to or even exceeds that of the variables (number of
luminaires), it is very likely that the optimization simply becomes overly stringent and
yields no feasible regain for an optimal solution. The over-constraining issue signifies
the critical link between degrees of freedom and scalability. In short, the scalability
potential of the lighting system depends more on the ratio of the luminaires and the
occupants than the size of the office or the total number of the luminaires. In practice, a
well-lit shared-space office generally has the proper number of luminaires appropriately
arranged to deliver designed lighting and it usually accommodates a reasonable number
occupants. Therefore, scalability of the system will not be an issue for a typical office.
Higher-level system design is necessary to make the current lighting control
system ready for practical realization. Although not considered in the previous tests,
exceptional cases have to be accounted for. One extreme would occur when the
available daylight alone already exceeds occupants’ lighting preferences. There will be
no way for the lighting system to generate light settings that counterbalance excessive
light. This worst-case scenario points to future research of integrating the automatic
shading system discussed in Chapter 10.3.2. The antithesis of the over-lit condition
arises when the occupants’ lighting requirements cannot be satisfied even if the settings
for electric lights have maxed out. This will most likely happen in legacy buildings that
are originally under-lit in the first place. Furthermore, the testing scenarios in the
previous sections assumed no change on occupancy status during the test. In reality,
occupancy change will certainly trigger new iterations of lighting optimization, where
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