Blinded by light!

Lighting up the night brightly until it almost disappears is a great achievement in terms of progress and technology, but what are the real effects of the disappearance of darkness? When humans alter the levels of light naturally present in the night-time environment we talk about light pollution. In other words, it is a pollution of natural light by artificial light.

Credits: NASA

As you can see from this famous NASA image of our Earth seen from space at night, light pollution is a problem that affects the most densely populated and industrially developed areas and causes various kinds of damage: environmental, cultural and economic. Astronomers and astrophiles were the first to point out this problem, as light pollution is a major obstacle to studying the sky. In 1958, the first law for the protection of dark skies was passed in America to protect an important observatory in Arizona. The problem is growing due to the increase in population and urban areas, so much so that astronomers have had to retreat to deserted areas in order to continue studying the sky.
Another very important aspect related to light pollution is wasted energy. Street lamps that waste light are the main cause of light pollution and can waste more than 50% of the energy they consume. Many street lamps used to light up streets and towns are inefficient because they do not use the light properly to illuminate the ground and make it possible to see at night. The remaining light that is not functional for night-time visibility is wasted because it either goes directly into the sky or becomes ‘intrusive’ light, disturbing people, plants and nocturnal animals. Far from being just a problem for astronomers and skygazers, in fact, light pollution causes considerable environmental damage such as difficulty or loss of orientation in animals (migratory birds, sea turtles, night moths); alteration of the photoperiod in some plants; alteration of circadian rhythms (e.g. the production of melatonin is blocked even at very low light levels) in plants, animals and humans; destruction of the (nocturnal) habitat of many animal species (bats, insects, reptiles).
How does light pollution spread? Light pollution radiates from the light source due to the presence of the atmosphere. Furthermore, the thicker and more opaque the layer of atmosphere through which the light passes, the greater the radiation. The atmosphere has the same effect on the light of street lamps as it does on the light of the Sun: it diffuses it, preventing us from seeing the stars. In fact, if there were no atmosphere, we would see the same starry sky during the day just as we do at night.
The five criteria for good lighting
Light pollution has many negative effects and no positive ones, except the possibility for astronauts to see the Earth shining from space! However, there are 5 basic criteria for proper lighting that can be applied to reduce light pollution and the problems it causes.
1ST CRITERION: How to Illuminate – Direct control of the light flux. The easiest way to reduce light pollution is to use shielded street lamps. These lamps are completely contained within the light fixture so that the light is not dispersed but only directed where it is needed. Such lamps are called ‘full cut-off’ lamps.
2ND CRITERION: How much lighting – Indirect light flux control. The second step to eliminate waste is to limit the amount of light used for lighting. It is necessary to gauge the power of the lamps in an optimal way, limiting light pollution. Of course, it will never be possible to zero out the amount of light that is scattered, because in order to be able to see at night, a certain amount of light radiation will have to ‘reflect’ upwards.
3RD CRITERION: What to use – High efficiency light sources. Modern, efficient light sources must be used to reduce energy waste. There is a parameter which indicates how much light is emitted by the source, as compared to other sources consuming the same amount of electricity. If an equal amount of electricity is consumed, preference must be given to sources that emit more light.
4TH CRITERION: Optimisation of lighting installations. The number of lampposts to be installed must then be assessed, optimising the distance between the poles and their height. The minimum ratio to be maintained by almost all Italian regional laws is 3.7, so for example 10 m high lampposts must be installed at least 37 m apart.
5TH CRITERION: Light management. The final aspect of saving energy and reducing light pollution is proper lighting management. Very often you see streets deserted at night or cycle paths brightly lit at any time of night. It is now possible to reduce lighting after a certain time of night and still ensure road safety. The lighting can be adjusted automatically using programmable devices (flow reducers). In this way, the lighting of roads with heavy traffic in the early evening, which therefore require strong illumination, can be reduced as the night progresses.

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