Light pollution occurs when artificial lighting (generally external) is excessive, misdirected or problematic. Too much light pollution will have repercussions. It washes out stars from the night sky, interferes with astronomical research, disrupts ecosystems and biodiversity, has harmful effects on health and wastes energy.

Just over 100 years ago, you could walk outside at night even in a city and see the Milky Way galaxy arch across the night sky. Witnessing thousands of stars was part of everyday life, inspiring artists such as Van Gogh or music composers like Holst or writers such as Shakespeare.

VAN GOGH Vincent, “Nuit étoilée sur le Rhône” (detail), oil on canvas, 1888, 72,5 × 92 cm.

Over half of the world’s population currently lives in cities and three out of four city dwellers have never experienced the wonder of an immaculate night sky. How can we explain to them the significance of what they have lost due to light pollution? How do we make them aware that light pollution is cause for concern on numerous fronts: safety, energy saving, cost, health and effects on fauna and flora as well as our ability to see the stars ? Finally, how do we convince them that it’s worth taking steps, however small, to help resolve this problem?

The effects of light pollution

By disrupting ecosystems, light pollution poses a serious threat, especially for nocturnal fauna, with negative impacts on plant and animal physiology. It can disrupt animal migration patterns, alter competitive animal interactions, change predator-prey relations and cause physiological damage. The pace of life is orchestrated by the natural daytime patterns of light and darkness, hence the disruption of these patterns impacts ecological dynamics.

With regard to harmful effects on health, numerous species depend on natural body cycles called circadian rhythms and melatonin production, which are regulated by light and darkness (e.g. day and night). The effects on health are not only due to over-illumination or excessive exposure to light over time, but also to the poor spectral composition of light (e.g. some colours of light).

In terms of energy wastage, lighting accounts for at least one quarter of all worldwide electricity consumption. Excessive lighting can be a waste of energy, particularly lighting that is directed upwards at night. Energy waste also constitutes waste in terms of cost and carbon footprint.

The good news is that light pollution can be reduced quite easily by protecting lamps properly, only using light when and where it is needed, only using the amount required and by using energy-efficient bulbs or lamps with the appropriate spectral power distribution for the task in hand.