The IAA develops a study that shows a decrease in light pollution in Granada during confinement

Although similar studies have been carried out in other countries, this is the only one that has obtained results thanks to the combination of observations from the satellite and from the ground




The periods of confinement imposed due to the pandemic produced by Covid-19 produced a clear and generalized decrease in environmental pollution in cities. A group of researchers, headed by the Institute of Astrophysics of Andalusia (IAA-CSIC), developed a project to measure the effects, which are more difficult to determine, of the decrease in lighting on light pollution, a problem derived from artificial lighting which has been related to damage to our health and that of ecosystems. And, indeed, they have detected lower levels of light pollution in the city of Granada during the state of alarm between March and May 2020.

This work reveals one of the shortcomings that sky quality experts already knew, related to one of the few spatial tools available for data collection. “If we compare satellite images before and during the confinement, hardly any changes are noticed, but if we look at data taken on the ground there we see something different, and for two main reasons: the satellite passes at dawn, when human activity has already stopped, and it is 'blind' to blue light, a range in which many of the LEDs used today emit”, points out Máximo Bustamante-Calabria, IAA-CSIC researcher who heads the work.

On the other hand, the data collected in Granada with photometers on the ground, equipped with different filters, show a clear decrease in the brightness of the sky during the first hours of the night, specifically of 20% in general terms and of almost 40% in blue light, mainly due to the decline in economic activity. On the other hand, at dawn the changes have been minor, with a reduction of between 5% and 10%, which is consistent with satellite data. The team has created a web application that allows to visualize in which places there has been a reduction in outdoor lighting that is in operation at dawn. Overall, the reduction has been minimal, with the exception of airports and a couple of cities.

“It is clear that the emission of light is closely linked to human activity, and this takes place especially before midnight, but we have confirmed that air pollution also plays a role. We have verified that there is an important correlation between the concentration of particles and the brightness of the sky, because aerosols and particles have an important role in the scattering of light. Thus, the decrease in brightness in the early hours of the night is mainly due to the absence of traffic during confinement and the transparency of the air, as well as the shutdown of private lighting. The small variation in the early morning tells us that the public lighting has not behaved differently from what it had programmed before the confinement”, indicates Máximo Bustamante-Calabria.

The study used DSLR cameras and 360 cameras to document activity on streets and facades and, in parallel, SQM and TESS photometers were used for continuous monitoring of sky brightness. “We see that, for the study of light pollution as an indicator of human activity at night, photometry on the ground is more useful for the moment, and especially in the blue band. In fact, our study is practically the only one that has been able to detect the effects of the state of alarm thanks to the use of data on the ground”, points out Alejando Sánchez de Miguel, a researcher at the IAA-CSIC and the University of Exeter who participates in the work.


Since the beginning of this century, the risks of light pollution have been documented, both for ecosystems and human health, due to the modification of the cycles of day and night: half of Europe suffers a generalized “loss of night”. The IAA has participated in pioneering studies that analyze the evolution and effects of light pollution and that showed, in 2017 and 2018 respectively, that the illuminated surfaces on the planet grow on average more than 2% per year, despite the introduction of more efficient lighting systems, and that exposure to blue light at night results in an increased risk of breast and prostate cancer. This field of study was accompanied by the creation of the IAA Sky Quality Office, to defend the dark sky as a scientific, cultural and environmental resource, and which has been the driving force behind this project in collaboration with the Granada City Council.



M. Bustamante-Calabria et al. "Effects of the COVID-19 lockdown on urban light emissions: ground and satellite comparison". Remote sensing 2021; 13(2):258

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Instituto de Astrofísica de Andalucía (IAA-CSIC)
Unidad de Divulgación y Comunicación
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