Humans create bright and safe living spaces at night by lighting various places, from city buildings to suburban roads. However, artificial night lights created by humans are said to adversely affect the behaviors of various animals.
It is estimated that the intensity of night light produced by humans and the degree to which light reaches it is increasing at a rate of 2-6% per year, and is noted to be one of the fastest growing pollutants in the world. Many organisms establish life cycles based on light such as the sun or the moon, but as light that originally did not exist at night is created, daily rhythms and hormones change, affecting different things such as sleep and mating.
For example, young sea turtles that have just hatched from eggs head towards the sea by relying on the moonlight reflected in the sea. However, if there are street lights along the beach, there are cases where they are attracted to the light and head inland. As a result, they can get hit by a car or drown in a swimming pool. Also, phototactic insects lose their sense of direction and crash into a street light, or fireflies emit light to attract males to disperse on street lights, making mating difficult.
In addition, studies have indicated that millions of birds are caught in city lights every year, suffer some harm or die. For bats that avoid light and some small mammals, environments exposed to human light are no longer habitat. In this case, the increase in street lighting is a form of habitat destruction.
On the other hand, for animals that normally forage only during the day, night light causes an extension of herbivorous behavior. This has the advantage of increasing the number of prey that can be caught, but studies using insect and spider stings have also indicated that night light reduces immune function or adversely affects growth, development and reproduction .
Recently, the adverse effects of human light have become well known, and efforts are being made to mitigate the effects on animals. In the state of Florida in the United States, in addition to changing the color of street lights near beaches in cities to amber, which is less likely to affect animals, street lights are said to be turned off during the turtle breeding season.
In addition to the adoption of amber lights on Phillip Island, Victoria, Australia, where the migratory bird Puffinus tenuirostris goes the longest distance, efforts are being made to switch off the lights along the migration route during the migratory bird crossing period . This strategy is said to have reduced the effects of night light on animals and saved the lives of countless animals.
Looking at behavior that can mitigate the impact on animals is to weaken the default brightness to illuminate only specific areas that really need light. Use sensors and dimmers to control the timing and brightness of lights. If possible, place the lights as close to the ground as possible and place a shield on the back to prevent the light from reaching an unnecessary range. As wildlife are sensitive to light with long wavelengths such as blue, purple and ultraviolet, choose light that has little effect on wildlife, such as red, orange and amber. If possible, the external walls of the building are finished with low reflective materials to prevent the reflection of scattered light.
In order to reduce the harm caused by light, it is only necessary to turn on the lights, but it is difficult to actually turn off the lights because humans have great benefits for work, leisure and entertainment. Instead, reducing the amount of lighting or changing the color can be a way to reduce even slightly the possibility of fatal effects on animals. Relevant information can be found here.
