  Bisei town, located in the west part of Japan, is known as a place where the
local community protects its beautiful night sky from light pollution through
its unique ordinances and the efforts of the local residents. It is also
important to monitor in the quantity and quality of light pollution for precise
measurement of astronomical observations. The fluorescent lamps in the city
were gradually replaced with light emitting diode (LED) lamps. In order to
investigate how much light pollution is affecting astronomical observation, we
analyzed the archival photometric and spectroscopic data taken by the 101cm
telescope that has been installed at Bisei Astronomical Observatory (BAO) since
2006. As a result, we found that there is no significant variability in sky
brightness in optical bands, but from spectroscopic observation, we observed a
blue humps around 4500 \AA originating from LED lights from 2017 to 2023. The
brightness of light pollution observed at BAO is not varied but the origin of
light has gradually changed from fluorescent lamps to LED lamps.
