Street light: It is the leaf part of the system where IoT nodes
are placed. Each streetlight is geographically localized on the city
map and uniquely associated to the IoT node attached to it, so that
IoT data can be enhanced with context information. The monitoring
of the correct operation of the bulbs is performed through
photometer sensors that directly measure the intensity of the light
emitted by the lamps (or, actually, by any source whose light
reaches the sensor) at regular time intervals or upon request. The
wireless IoT nodes are also equipped with temperature and
humidity sensors, which provide data concerning weather conditions,
and one node is also equipped with a benzene (C6H6 )
sensor, which monitors air quality. IoT nodes are generally
powered by small batteries, though connection to a low-power
grid is required by the benzene sensor. The packaging of the
sensor nodes has been designed by considering the specific
requirements of this use case. Indeed, sensor nodes have been
hosted in a transparent plastic shield that protects the electronic
parts from atmospheric phenomena (such as rain or snow), while
permitting the circulation of air and light for the correct measurement
of humidity, temperature, and light intensity.