Evaluation of the safety of conventional lighting replacement by artificial daylight.pdf

Background: Short morning exposure to high illuminance visible electromagnetic radiations termed as
artificial daylight is beneficial for the mental health of people living in geographical areas with important
seasonal changes in daylight illuminance. However, the commercial success of high illuminance light
sources has raised the question of the safety of long hour exposure.
Methods: We have investigated the effect of the replacement of natural daylight by artificial daylight in
Swiss mice raised under natural lighting conditions. Mice were monitored for neurotoxicity and general
health changes. They were submitted to a battery of conventional tests for mood, motor and cognitive
functions’ assessment on exposure day (ED) 14 and ED20. Following sacrifice on ED21 due to marked
signs of neurotoxicity, the expression of markers of inflammation and apoptosis was assessed in the
entorhinal cortex and neurons were estimated in the hippocampal formation.
Results: Signs of severe cognitive and motor impairments, mood disorders, and hepatotoxicity were
observed in animals exposed to artificial daylight on ED20, unlike on ED14 and unlike groups exposed
to natural daylight or conventional lighting. Activated microglia and astrocytes were observed in the
entorhinal cortex, as well as dead and dying neurons. Neuronal counts revealed massive neuronal loss in
the hippocampal formation.
Conclusions: These results suggest that long hour exposure to high illuminance visible electromagnetic
radiations induced severe alterations in brain function and general health in mice partly mediated by
damages to the neocortex-entorhinal cortex-hippocampus axis. These findings raise caution over long
hour use of high illuminance artificial light.