Due to the Tohoku earthquake in March 2011, many offices ¯
and educational facilities have to reduce electricity usage by
15%. For example, Keio University reduced usage by setting
the temperature of air conditioners to 28◦C in the summer
time and cut down the usage of lights in offices.
Lighting constitutes about one third of the total electric
power consumed in university campuses. It is, therefore, essential
to quantify the wasteful lighting in a room. Due to their
low cost and non-invasiveness to human privacy, PIR sensors
are a good candidate for room occupancy determination. Commercial
products which use PIR sensors for automatic light
control already exist but these products are intended to detect
short-term occupancy in small spaces such as washrooms and
corridors.