Helena Joyce
Light pollution is a growing problem, and it is important to be able to measure it to understand its impacts and find solutions. Artificial light at night (ALAN) has various benefits, but it also has adverse effects on astronomy, epidemiology, and ecology. There are several ways to test and measure light pollution, including ground-based observations and remote sensing by satellites. While there is no single device that meets all measurement objectives, tools like light pollution filters and the Bortle scale, which measures the brightness of the night sky, can help assess light pollution levels. Citizen science projects like Globe at Night and Cities at Night also contribute valuable data by enlisting the help of volunteers to measure sky brightness and identify light pollution in photos of cities.
| Characteristics | Values |
|---|---|
| Definition | Light pollution is the human-made alteration of outdoor light levels from those occurring naturally. |
| Sources | Streetlights, greenhouses, and satellites are among the many sources. |
| Effects | Light pollution has harmful effects on humans, wildlife, and the climate. |
| Measurement Tools | Tools used to measure artificial light at night include satellite remote sensing, smartphone apps, sky quality meters, and light pollution filters. |
| Measurement Challenges | The variability of Earth's atmosphere, limitations of measurement tools, and lack of unified measurement techniques, units, and terminologies pose challenges. |
| Mitigation | Properly designed lighting, establishing codes and statutes, and public education can help reduce light pollution. |
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What You'll Learn
Using a light pollution filter
Light pollution filters are an effective way to reduce light pollution in photographs. They are particularly useful for astrophotography, nightscape photography, and landscape photography. Light pollution filters selectively block certain wavelengths of light, specifically the yellow and orange parts of the spectrum between 575nm and 600nm, which are the common colours of sodium vapour lights used in streetlights.
There are various light pollution filters available, and the right one for you will depend on your unique imaging location. For example, if you are surrounded by yellow sodium vapour lights, you will need a different filter from someone surrounded by blue-white LED lights. The Optolong L-Pro filter, for instance, is designed for moderately light-polluted areas, and it includes a mild filter against known artificial light sources, including LED street lights. It also preserves the natural colours of stars in the night sky. The Optolong L-Quad Enhance Filter is another option, which captures natural-looking images while blocking major light pollution emission lines.
When testing light pollution filters, it is important to consider both optical performance and general build quality. You should test light transmission levels, colour neutrality, and the impact on image quality. Comparing the transmission graphs of each light pollution filter is a great way to decide which filter is right for you.
Light pollution filters can be a fantastic tool for improving your nighttime photos, but it is important to note that they work better under dark skies in remote locations. Even with a filter, it will not be possible to capture the Milky Way Galaxy or the Orion Nebula from the centre of a big city.
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Mapping light pollution
There are several methods and tools available for mapping light pollution, each with its advantages and limitations. One common approach is to use ground-based measurements, which involve placing instruments on the ground to measure the amount of artificial light at night (ALAN). This method provides detailed data but may be limited by the number of measurement stations and their locations.
Remote sensing by satellites is another valuable technique for mapping light pollution. Satellites in Earth orbit can capture comprehensive data on ALAN, providing a broader perspective than ground-based measurements alone. However, the variability of the Earth's atmosphere can make it challenging to compare datasets from different satellites or locations.
Citizen science projects also play a crucial role in mapping light pollution. For example, the Cities at Night project invites volunteers to map and identify photos of cities taken from the International Space Station, contributing to a global understanding of light pollution. Additionally, smartphone apps like Globe at Night allow users to participate in long-term monitoring efforts.
Online platforms, such as Light Pollution Map, utilize base light pollution data from sources like NOAA's VIIRS to create interactive maps. These maps are colour-coded, with Bortle classes ranging from Class 1 (pitch black) to Class 9 (heavily light-polluted), making it easy for users to identify dark sky spots and suitable stargazing locations.
By combining these various mapping techniques and tools, scientists, policymakers, and communities can work together to address light pollution effectively, minimizing its negative impacts and preserving the natural nighttime environment.
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Understanding the causes
The excessive use of outdoor lighting at night has various adverse effects. For instance, it disrupts human circadian rhythmicity and harms wildlife and the climate. It also poses a threat to ground-based observatories by reducing the visibility of stars and other celestial objects.
To address light pollution, it is essential to have a thorough understanding of its magnitude. This can be achieved by measuring the brightness of the night sky. One way to do this is through remote sensing by satellites in Earth orbit. Citizen science projects, such as Globe at Night and Cities at Night, also contribute to measuring sky brightness and understanding light pollution's impacts. These projects involve citizen scientists using tools like sky quality meters and smartphone apps to collect data and map light pollution.
Additionally, it is important to consider the lighting characteristics that contribute to sky glow. For example, the conversion to blue-rich LED lighting in distant towns can cause light pollution colour changes, impacting rural skies. The increasing radiance and extent of artificially lit surfaces at night further exacerbate the problem.
While there is no single device that meets all measurement objectives, tools like light pollution filters and the Bortle scale can help assess light pollution levels. However, it is crucial to acknowledge the limitations of each tool to avoid incorrect conclusions.
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Assessing the impact
Measure Sky Brightness: One way to assess light pollution is by measuring the brightness of the night sky. The Bortle scale, for example, is a tool used to determine the quality and brightness of the night sky in a particular location. Citizen science programs like Globe at Night also contribute to this effort by collecting data on sky brightness to raise awareness about light pollution.
Remote Sensing and Satellites: Remote sensing technologies, including satellites in Earth orbit, play a crucial role in monitoring light pollution. These tools provide valuable data on the extent and intensity of artificial lighting across the globe. Projects like Cities at Night utilize citizen scientists and images from the International Space Station to map light pollution.
Ground-Based Measurements: Ground-based measurements are also essential for assessing light pollution. This includes the use of sky quality meters, which measure the brightness of the night sky, and light pollution filters, which can enhance astrophotography in light-polluted areas. Basic techniques include comparing the quality and detail of images taken under different sky conditions, which can provide a qualitative understanding of light pollution levels.
Collaborative Efforts: Addressing light pollution requires collaboration between different disciplines. Organizations like DarkSky International work with communities and professionals to establish codes and statutes that reduce light pollution. They also advocate for proper lighting practices that are beautiful, healthy, and functional. By uniting diverse stakeholders, we can develop unified measurement techniques and terminology to combat light pollution effectively.
Health and Environmental Impact: Light pollution has been shown to disrupt human circadian rhythms, affecting our health and well-being. Additionally, excessive artificial light can harm wildlife and impact the environment. Assessing these ecological and health consequences is crucial for understanding the full impact of light pollution and developing strategies to mitigate its negative effects.
By employing these methods and working together, we can effectively assess the impact of light pollution and strive towards creating darker, more natural night skies.
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Choosing the right tools
When it comes to choosing the right tools to measure light pollution, there are a variety of methods and devices available, each with its own advantages and limitations. Here are some key considerations to help you select the most suitable tools for your specific needs:
Remote Sensing and Satellites
Remote sensing by satellites in Earth orbit is a widely used method for measuring light pollution. Satellites can provide valuable data on artificial light levels and their impact on the night sky. This method offers a comprehensive view of large areas and helps researchers assess light pollution across the globe.
Ground-Based Measurements
Ground-based measurements are another approach to quantifying light pollution. This can involve using instruments such as sky quality meters, which are placed in specific locations to measure the brightness of the night sky. These measurements can be influenced by factors such as atmospheric conditions and the proximity to light sources, so proper instrument placement and experimental reporting are crucial.
Imaging and Photography
Imaging tools, including cameras and smartphones, can be used to capture the effects of light pollution. By comparing photographs taken under different light-polluted conditions, you can assess the impact of artificial light on the visibility of celestial objects. Imaging can also be used in citizen science projects, such as the Cities at Night project, where participants contribute images to help map light pollution.
Light Pollution Filters and Astronomy Apps
Light pollution filters can be used in conjunction with cameras to reduce the impact of light pollution on astrophotography. These filters enhance the visibility of celestial objects even in light-polluted areas. Additionally, astronomy apps, such as 'Clear Outside', can provide information about light pollution levels based on your coordinates.
The Bortle Scale and Light Pollution Maps
The Bortle scale is a widely recognised method for quantifying the quality and brightness of the night sky in a particular location. It ranges from Bortle 1 (excellent dark-sky site) to Bortle 9 (inner-city sky). Light pollution maps utilise the Bortle scale to visually represent the levels of artificial light pollution in different areas, with colours ranging from red (high pollution) to green and blue (low pollution).
It is important to note that no single device meets all measurement objectives, and each tool has its limitations. By combining different methods and tools, you can gain a more comprehensive understanding of light pollution in your area and contribute to the growing body of research in this field.
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Frequently asked questions
Light pollution is the human-made alteration of outdoor light levels from those occurring naturally.
Artificial light at night (ALAN) is ever-present in modern society and has various benefits. However, it can also have adverse effects, causing light pollution.
Light pollution can negatively impact human health, the environment, and stellar visibility. It can disrupt human circadian rhythm and prevent people from experiencing a natural night.
You can assess light pollution in your backyard by examining the brightness of the night sky. The Bortle scale is a tool used to measure the quality (brightness) of the night sky in a particular location. You can also use a light pollution filter or a sky quality meter.
You can support organisations like DarkSky International, which works to restore the nighttime environment and protect communities and wildlife from light pollution. You can also participate in citizen science projects like Cities at Night, which uses photos from the International Space Station to map light pollution globally.
