One of the main causes of light pollution is the excessive and improper use of outdoor lighting. The ways to reduce the light pollution include reducing the use of improper outdoor lighting, limiting the duration of lighting, improving the lighting designs, and chancing the intensity and spectrum of lighting sources.
The rule of thumb is using lighting reasonably: do not set up unnecessary lighting. The most effective method is preserving natural unlit areas by avoiding excessive and unnecessary lighting in those rural areas. Since unnecessary lighting not only pollute the sky through direct illumination, but also contribute to skyglow. Improperly installed illuminations can induce artificial skyglow tens, and possibly hundreds, of kilometers away.
Although this approach will often conflict with economic interests, especially in developed urban cities, there are already implanted dark sky areas that successfully protect turtle hatchling from being disoriented by artificial lighting and bird strikes.Competitive interactions between artificial lighting and natural cues during seafinding by hatchling marine turtles
Saving energy and reducing light pollution can both be achieved by turning off useless lighting. It is also an effective alternative when removal of excessive lighting is not possible.
We are not implying that you should live in the dark, rather just switch off or dim the lights during particularly critical times can simply achieve the target, so-called part-night lighting. Critical times include periods when biological activities are significant, such as foraging, breeding and migratory periods.
Turning off the neon signboards on the streets at midnight, reducing the hours of floodlight on golf courses, road lights in country parks and decorative lights on buildings are all possible ways being considered by government and organizations. For example, in Devon, UK, many rural towns will have no lights on between dusk and dawn.
For more delicately designed ‘adaptive’ lighting systems, the level of light is adjusted according to the movements of people and vehicles. In Germany, lighting can also be provided for short periods on request through network.Street Lighting for Devon
For lighting that must be turned on for the whole nights, proper designs must be implanted in order to minimize the influence. Dark-sky friendly lighting designs consider pointing direction and shading.
In terms of pointing directions, upward lighting is definitely useless and wasteful, causing light pollution. For example, it is easy to see that the clouds just above the buildings that equipped with upward outdoor lighting are brightened. According to the statistic from International Dark-Sky Association, 30% of outdoor lighting in U.S. are pointing upward, which wasted more than 1.5 million kWh of energy and 6 million tons of coals each year. In France, public lighting on average represents around half of municipalities’ consumption of electricity equivalent 6TWh consumption per year. Global warming due to the combustion of fossil fuel is hence enhanced and degraded our environment further more.
Moreover, we should not underestimate the influence of horizontal and near-horizontal lighting. It is because such lighting setup will increase the visibility distance of light sources, hence increase the potential of disrupting animal activities, and significantly increase the unintended illumination area. Also, as the light path is longer, the skyglow produced by scattering will be much more serious than those of upward lighting.
Install proper light shade is a cost-effective alternative. Poorly designed lampshades allow a portion of light scattering up instead of down. The better design of lampshades, like the so-called "Full-Cut-Off Lighting" or "Down Lighting", should focus the light energy to 0 to 65 degrees downward, meaning that minimum light is pointing upward and hence reduce light pollution. Also, lighting costs would be saved by replacing light bulbs with lower power consumption to achieve required intensity.
Shading is not only restricted to light sources. Building structures or planting vegetation to shield sensitive areas against light is another feasible option. Also replacing reflective surfaces with light absorbent materials can help reduce scattered light.
On the other hand, if the light sources are simply too bright, no matter how good the lighting are designed and installed cannot improve the situation. In the absence of light pollution, full moonlight under clear skies gives a typical illumination of 0.2 lux, which should be the brightest natural situation. However, typical street lighting give excessive illumination level between 10 and 60 lux. It is because over-bright sources are used to make the area between lamp posts just bright enough but make the area under the posts too bright. With careful planning, a much more uniform, intermediate level of illumination will be enough for security and safety purposes.
Traditional lighting, e.g. light bulbs, emit light in full spectrum; nowadays, we have lighting devices that can emit selected spectrum. Different spectra of light may have different effects. For instance, blue light may suppress the production of melatonin and affect the circadian rhythm in many species. Appropriate spectral composition of light can suit to different requirements of dark sky. For instance, Low Pressure Sodium (LPS) Lamps are good for astronomical observations as the emission lines of LPS occupy a small portion in visible spectrum only. Astronomers can easily filter out its lines by applying filters.
For organisms, as different species have different visual systems that are sensitive and responsive in different wavelengths. Specially selected light sources can illuminate the area for human activities but not affecting the animals. For example, sea turtle avoid nesting at areas that are lit with white mercury-vapor lamps, but not narrow spectrum LPS lamps. Also many animals are sensitive to UV, which they use to choosing mates and flower recognition in pollinators, etc., light sources that emit abundant UV should be avoided.The spectral input systems of hymenopteran insects and their receptor-based colour vision Author(s): Dagmar Peitsch, Andrea Fietz, Horst Hertel, John de Souza, Dora Fix Ventura, Randolf Menzel