Impacts of artificial light on nocturnal integrity and human health
Impacts of artificial light on starry sky
Starry sky splendor has always fascinated humans. Its contemplation is the source of the extraordinary creativity that our species have known throughout the years in arts and sciences areas. Today in industrialized country, the majority of the population has never seen a great starry sky. Since the electricity advent, artificial light at night (ALAN) did not stop growing.
In 2001, Cinzano  and his collaborators published the first worldwide atlas talking about light pollution with data base on survey satellite from 1996-1997 (Fig.1).
Light pollution all around the world. Light pollution levels are expresses in function of a ratio: artificial light/ natural artificial light of a starry sky. The ratio is reported according to different colors (ratio: blue:0.11-0.33; green:0.33-1; yellow:1-3; orange:3-9; red: 9-27; white: 27 and over). Credit: P. Cinzano, F. Falchi (University of Padova), C. D. Elvidge (NOAA National Geophysical Data Center, Boulder). Copyright Royal Astronomical Society. Reproduced from the Monthly Notices of the RAS by permission of Blackwell Science.
According to this atlas, 18.7% emerged land all around the world, 61.8% of the United-states of America (excepting Alaska and Hawaii), and 85.3% of European area whose 98.9% of the French area is affected by light pollution. Considering geographical repartition of human population, this atlas report that 62% of global population whose 99% of United-States population (excepting Alaska and Hawaii) and 100% of French population is affected by light pollution. This atlas also reports that 28% of global population, 81% of United-States population (excepting Alaska and Hawaii), 68% of European Union population and 64% of the French population were exposed to light pollution equivalent to a full moon light by a clear sky, it means a permanent fully moon. Finally, 9% of global population, 44% of United-Sates population (excepting Alaska and Hawaii), 17% of European Union population and 22% of French population were exposed to light pollution such as their vision cannot adapt to a night vision, it means that their visual system was always in twilight vision or in day light vision.
This rise of ALAN has an considerable impact on starry sky. Artificial sky glow forbid the stars observation. We are estimating that more of 97% of stars are now imperceptible with unaided eye in industrialized centers and big cities all around the world. The major cause of this phenomenon is the multiplication of the street lights. Light emitted by light sources is diffused in the atmosphere and interacts with particles in air suspension (Fig. 2). This diffusion formed light halos that are hiding the night sky and disturbed night integrity.
The apparition of street light using light emitting diode, rich in blue light, diffused more in the atmosphere that the one using high pressure sodium (HPS) and contribute substantially to the rise of light pollution.
The major impact is the degradation of the quality and accessibility to starry sky, a natural heritage endangered.
Figure 2. The light from artificial sources hit the molecules and aerosols suspended in the atmosphere and is reflected to the ground. This diffusion of light generates a cloud of light that prevents observation of the night sky.
Impacts of ALAN on Flora
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