Light pollution: “We need national awareness”

Decade after decade, light pollution has been on the rise. So much so that the number of stars visible to the naked eye after dark could halve in some places in less than twenty years, a study published last January showed in the journal The science.

To estimate the effect of artificial light on the night sky, the scientists relied on stargazing observations made between 2011 and 2022 by about 51,000 citizen scientists, mostly in the US and Europe. From these observations, the researchers were able to conclude that the brightness of the sky increased annually by an average of 9.6% in the places where the participants lived. Specifically, a child born today in a place where 250 stars are visible at night will only be able to see a hundred by the age of 18.

An observation that raises questions, especially since the impact of artificial light on living things in a broad sense goes far beyond the observation of the starry sky. To learn more, TF1info contacted Anne-Marie Ducroux, President of the National Association for the Protection of the Sky and the Night Environment (ANPCEN).

For over 20 years, your association has been campaigning to limit exposure to artificial light. Were you surprised by the results of this study?

Anne-Marie Ducroux: Initially, these researchers showed an average growth of 2% per year. In their latest study, they indicate that on average it will be 10%, and this figure surprises them. But we are surprised, to tell the truth, that they are surprised: we know that for years there has been an underreporting of light pollution, private lighting – billboards, illuminated signs, etc. – are not taken into account due to the lack of available data. In just 20 years (between 1992 and 2012), street lighting alone increased the number of light points in street lighting by more than 89%, giving 94% more artificial light at night.

Light pollution caused by the proliferation of artificial light sources affects both cities and the countryside. Are there black nightclubs in France?

It is often believed that only large cities produce light. However, it is not. Light is scattered far from sources, for tens and tens of kilometers around. In 2015 we published a map of light pollution in France. We clearly see that there are still very few places where we have good night quality. These are either uninhabited areas, for example, in the mountains; or areas of very low population density, the “diagonal of the void” as it is called in France. All communes are too enlightened compared to the reality of the biological rhythm we need. Hence the importance of reducing the amount of light in all municipalities. But for that, we need national awareness. In fact, if a municipality operates at its best, but all the municipalities surrounding it do nothing or increase the number of lights, its efforts will decrease significantly. In other words, a comprehensive approach is needed.

The study, published in the journal Science, coincided with the replacement of many outdoor lighting fixtures with light-emitting diodes (LEDs). Because of the energy savings they provide, this technology is often referred to as environmentally friendly. You say it’s heresy. For what ?

LEDs have a higher light output than technologies that have been used before and therefore allow for energy savings, hence the fact that they are said to be adorned with environmental claims. What we observe on earth is that the points of light are multiplying. The elect say to themselves: since we save energy, we can invest even more. It is in the millions every year, which leads to a very strong contribution of LEDs to the increase in the amount of artificial light. Since they are often misdirected, some of the light is directed towards the sky, which amplifies the phenomenon. In addition, LEDs use a color temperature with a very strong blue component, which we know will be highly toxic to both humans and fauna and flora.

The effects of artificial light are numerous and affect humans as well as animals or insects and even plants. What are the consequences?

Physiologically, in order to live better and be healthy, people need to be in the sun for long periods of time during the day and sleep in complete darkness at night. Today, however, we live upside down most of the time. This biological imbalance affects hormone production, lowers our immune defenses, and disrupts mood regulation. In terms of wildlife, we have published a study that shows that it affects all species groups, from birds to botanists, including reptiles, fish, and even plankton. Like us, they have a biological clock that is driven by light and the cycle of day and night. By making the night look like day, we have disrupted this natural biological rhythm. But it is on this that life has been built for millions of years. We also know that light pollution is the second killer of insects. There was a 62% difference in the pollination of the two plots between the illuminated and unlit plots. These pollinators play an important role, because without them, remember, fruit trees do not bear fruit.

Today, pollution is recognized in national reference texts. Ten years ago this was not the case. Is this awareness of the effects of light pollution translated into action?

Today, mayors are increasingly aware of the problems associated with light pollution. Currently, about 12,000 cities go offline in the middle of the night. This is the solution we’ve been recommending for years, as it’s the easiest and least expensive. With rising energy prices, this is an additional lever to reduce urban lighting and, at the same time, light pollution associated with it.