To capture breathtaking pictures, light is probably the most important component of a scenery. While landscape photography mostly relies on natural light, artificial light sources enhances life quality in countless applications and situations. But there is a downside in artificial light and as the world population keeps increasing and causes urban areas to expand, the problems became bigger in the recent years.
While most of the artificial light sources have a reasonable purpose such as public safety, there are also as many light sources in less mandatory applications, such as decoration or advertising. In addition, even mandatory light sources are often badly designed and emits a major part of their light into the night sky instead in the direction the light is needed.
The term light pollution means the continuously presence of artificial light. The amount of artificial light differs highly between different areas. The Bortle scale is one helpful tool to categorize the amount of artificial light in a particular area. The scale is split up in 9 classes. The night sky at a site with excellent and truly dark sky is classified as a Bortle class 1 sky. When only the brightest stars are visible, e.g. in an inner-city area, the sky is classified as a Bortle class 9.
Example 1: city lights
The picture above demonstrates how the lights of a city illuminates the night sky and as well the surrounding mountains. The bell-shaped light emission over the city is clearly visible and stretches way over the mountains into the night sky.
Example 2: reduced visibility of lower sky
This picture illustrates how the light pollution in particular affects the visibilty of stars close to the horizon. The visibility in the higher sky is way better, however the picture suffers from the orange stripe between the foreground and the milk way.
Example 3: visibility of zodiac light
The zodiac light can only be seen in places with a very dark sky (typically Bortle class 4 or lower). In the picture above, the zodiac light extends from the center of the image to the top left corner. It is a glow of scattered sunlight, caused by interplanetary dust.
The growth of plants can be effected, as the the presence of artificial light disturbs the interpretation of the length of day and night. Many insects get irritated by artificial light, this already lead to exstinction of nocturnal insect species. Also night-flying birds may loose orientation due to light pollution.
Apart from animals and plants, also humans experience negative impacts with light pollution such as insomnia.
As mentioned above, the visibility of stars higly relies on a dark sky. In densly populated regions and countries, places with low light pollution became very rare and are often very hard to get to. Light emissions of urban areas and cities can be observed from a far distance and turns the night sky close to horizon into orange, making it impossible to see or photograph astronomical objects in the lower night sky.
Energy & money
Generating not required light also wastes energy and money.
Reducing the light pollution is very easy. There are just a few points to consider and everyone can contribute to protect and recover dark night skies.
turn off lights when they are not needed
reduce the brightness of light to the minimum required level
let your lights point downwards
shield you lights and therefore avoid emitting useless light into the sky
use warm lights (3000K or below) instead of the cold (labled as "natural" or "dayligh") ones
A very important and effective contribution is also to advocate this topic with friends and family.