Did you know that in addition to soil, atmospheric and acoustic pollution artificial light can have serious environmental consequences for humans, wildlife, and our climate?

Our research projects try different approaches to measure and study light pollution.

Light pollution

Artificial lighting alters the environment´s natural pattern of light and darkness. It is produced by all sources of light and it is especially noticeable in the brightness of the sky. We try to lengthen the day artificially setting excessive artificial lighting, generating a waste of energy and money without being aware that it generates harmful effects on people’s health, animals and plants.

Natural darkness is disappearing and that generates a series of negative consequences.

Light pollution not only prevents us from seeing the stars, but it also affects our health, safety and the environment.

Negative effects of artificial light

Affects safety and security

Brighter does not mean safer!

Strong lighting generates a psychological sense of safety and security, but this does not necessarily mean that real safety and real security have actually increased. 

For example, if the lighting is not uniform and dark areas are combined with strongly lit areas it will cost us more effort to distinguish objects around us and this consequently decreases our safety. On top of that, too bright or poorly directed lighting can cause glare, which is especially dangerous on roads.

Alters ecosystems

Artificial light affects animals and plants negatively, damaging nocturnal habits by altering the biological rhythms of the species.

The vast majority of living beings use natural light and dark cycles to regulate some of their behaviours related to reproduction, feeding, sleeping or finding protection against predators. Artificial light at night has negative and sometimes fatal effects on many creatures including mammals, amphibians, fish, insects and birds.

The stars are vanishing

For those of us who live in cities, the night is no longer dark and many of us have forgotten that above our heads we should be able to see thousands of stars.

Many people have never seen the Milky Way and do not know that a starry sky without a moon emits enough light to be able to go for a walk in the countryside. Just the light of the stars is enough to make you cast a shadow. And a dark sky can be so spectacular it can turn any random place into a holiday destination.

The increase in skyglow, caused by the dispersion of artificial light in the gases and particles of the atmosphere, cause a deterioration in astronomical observation conditions. And migratory species that use the stars to orient themselves are negatively affected as well.

Effects on health

Have you ever noticed how hard it is to fall asleep after having used your cellphone in bed for a while?

Humans need light by day and darkness by night in order for our biological clocks to work properly. Only when we are in the dark does our body secrete a hormone called melatonin that plays an important role in the regulation of circadian rhythms and sleep.

Computer and television screens as well as other electronic devices emit artificial light. Using these devices until  late at night alters and prevents us from generating the melatonin we need. The mismatches in the segregation of melatonin can lead to problems such as stress, insomnia, diabetes and even obesity.

Sky brightness is increasing in the cities.

Types of light polllution


Glare is caused by a light intensity that is too high or by badly directed light. It can cause discomfort and partially impaired vision. To explain in more technical terms; Glare causes for a photochemical reaction to occur on the retina of the eye making the eye temporarily numb.

Some examples of light that can produce glare are the flash of a camera or a flash of lightning during a thunderstorm.

Light trespass

Although street lights are meant to illuminate the streets, many poorly directed street lights shine into our homes and prevent us from sleeping in darkness.

Although, using roller shutters to cover the windows can stop the light from coming in, in hotter regions they are not convenient during the summer when the heat forces people to open windows and shutters during the night.

Brightness of the sky

Cities are generally bright. The light, when refracted in the molecules of our atmosphere, becomes diffuse and this prevents us from seeing the stars.

Out in nature where it’s dark, night clouds appear to be black in colour. In large cities, however, they reflect the light directed towards the sky, consequently the clouds will start to appear orange or blue depending on the colour of the city lights.


Too much luminous advertising on roads can be dangerous as it might distract drivers.

Increasing the light intensity does not necessarily make roads safer. Installing an evenly spread uniform illumination definitely does make them safer as it allows people to see more clearly.

Las Vegas, Nevada (USA) is one of the most illuminated cities on the planet. Its brightness can be observed from 400 km away.

Light generates a psychological sense of security that may or may not be associated with the real one.

How to install efficient lighting

Every place and situation have lighting needs. The same lighting is not needed during an operation in a hospital operating room than in our bedroom just before going to sleep.

To use only the necessary lighting for each place and situation, so that its use is sustainable and generates the minimum negative impact, a series of guidelines must be followed according to its different characteristics.


Artificial light must be aimed properly at its target. Directing the light only to the place where it is needed is very important, especially outdoors, since emitting light in other directions is not only a waste of energy but has negative impacts for both the sky and ecosystems.

Street lamps are meant to illuminate roads or squares. And when lighting up a building the light should never point upwards so to avoid lighting up the sky with the reflection onto the facade.

“Balloon-type” street lamps are extremely inefficient. It is better to use shielded street lamps with the bulb installed horizontally and the flux luminous directed downwards.

Color temperature

Bulbs can emit light with different “colour temperature”, which is measured in Kelvin. The light is warm if its colour is orange or reddish and cold if white or blue colours predominate.

If we install warm lighting in our bedrooms and in relaxing areas we will help our body to generate the melatonin it needs to rest. Ideally, 2700K light bulbs should be chosen for the rooms where there is some activity while 2200K light bulbs are more adequate to use just before bedtime.

When performing activities that require a lot of precision or that are performed in the light of day the use of cooler lighting will help us as it allows us to make a clearer distinction between colours.

Comic credit: Rainer Stock


Light bulbs consume electricity. The energy consumed every second is called power, and it is measured in watts (W) in theInternational System of Units.

Of all the electrical energy consumed by a lamp while on, only a fraction becomes light. Some of the energy degrades into heat and some of it is emitted as non-visible radiation.

The fraction of energy that is transformed into visible light, every second, is called radiant flow and its unit, in the International System, is also the watt.

The sensitivity of the human eye varies according to light intensity. The perceived light power is called flux luminous, and in the International System of Units it is measured in lumen (lm).

This content is part of the didactic unit
Cities at Night. Citizen science for the
location of light pollution sources

Lucía García – lucia_garcia@ucm.es
Alejandro Sánchez de Miguel – pmisson@gmail.com