Light Pollution Filters: A Photographer’s Guide

Astrophotography is still one of the most popular photographic genres in the world and as we are in the middle of the Milky Way season, it is a very good opportunity to take a deep look into a very useful accessory for many best photos of the night sky.

In this article we will analyze the effect and use of a light pollution filter, a very useful tool in the hands of not only astrophotographers but also low-light photographers.

Contents

What is light pollution?

“Light pollution is a side effect of industrial civilization,” writes the International Dark Sky Organization. “Its sources include exterior and interior building lighting, advertising, commercial properties, offices, factories, streetlights and lighted sports venues. […]”

“That light, and the electricity used to create it, is wasted spreading it across the sky, rather than focusing it on actual objects and areas that people want to illuminate.”

In addition to blocking our view of the night sky, it also has serious environmental consequences on the whole ecosystem, but also affects human health.

Altitude 1800m
Altitude 2300m

The yellow/orange tint near the horizon is the effect of light pollution in the photos above.

Most people are not aware of this type of pollution, but it is very important for human health and the whole ecosystem to raise awareness and know more and take action even in our homes to try to reduce it.

What is a light pollution filter?

A light pollution filter is a filter that blocks a specific part of the wavelength, and more specifically it cuts out the yellow and orange parts of the spectrum between 575nm and 600nm, without altering other colors/wavelengths.

Yellow and orange are the most common colors of sodium vapor lamps used in most major cities around the world, and since most of us live in a major city or have one near us, this filter can help us reduce the levels of light pollution that are recorded on our shots.

Streetlights are a big source of yellow and orange light pollution.

The design of light pollution filters

A light pollution filter looks like a common UV filter at first glance, but its glass has a slight purple or green tint depending on the manufacturer, and is usually made of didymium, which is a mixture of the rare earth metals praseodymium and neodymium.

The filter is ideal for astrophotography because in addition to blocking unwanted yellow and orange tones from light pollution, it also increases overall image contrast and enhances red and magenta tones in captured photos.

Orion Nebula at 35mm without lens filter.
Orion Nebula at 35mm with a light pollution filter.
Orion Nebula at 85mm with a light pollution filter

How the Light Pollution Filter Affects Photos

The basic principle of astrophotography is to find a location away from city lights to capture the beautiful night sky in all its glory. Yet, as our civilization continues to advance, artificial light can be seen almost everywhere – even if we are in a remote location, some light or its glow will likely still be visible.

By using a light pollution filter, the effect of light pollution, which can usually be seen near the horizon as a yellow/orange tint, is reduced or even eliminated in shots.

A scene captured with a lens filter.
The same scene captured with a light pollution filter. Please note that white balance has nothing to do with the effect of this filter.

Side effects of light pollution filters

There are many excellent light pollution filters on the market and most of them can reduce light pollution levels on our shots, but depending on the manufacturer and build quality of the filter there are some side effects. which we will discuss in more detail.

Light transmittance

As this filter blocks a specific part of the wavelength, it also reduces the overall transmission of light. This means that with this type of filter, some exposure compensation is needed either on camera during shooting or later during post processing.

Most filters typically block about half a stop of light, with higher quality options at 1/3 stop reduction and lower quality options at nearly 2/3 stop.

For newer cameras, even 2/3 of a stop isn’t a big deal, but it’s still something to consider when deciding which filter to buy.

No filter.
Captured with a light pollution filter.

Artifacts

Higher quality filters generally offer excellent optical elements with a multi-coating that will reduce any visible optical aberration and in-photo artifacts such as flare and/or ghosting.

Notice the small glow in the center of the image.

Tint

Some filters produce an unwanted tint/color in the captured photo, but in most cases this is something that can be easily fixed in post.

Captured with a high quality light pollution filter.
Captured with a low quality light pollution filter with a green tint.

Low-light urban photos with a light pollution filter

Here are some examples of low-light urban photos captured using light pollution filters.

No filter.
Light pollution filter.
No filter.
Light pollution filter.

Filter against light pollution during the day?

As we mentioned at the beginning, a light pollution filter can also improve overall image contrast and also increase saturation in red and magenta tones. These are things that can be very useful during the day – when shooting at sunset, for example.

Conclusion

Another thing to keep in mind is that the light pollution filter works best under dark skies (in remote locations). Even though it can also be used in (heavily) light polluted areas, it will still not be possible to capture the Milky Way or the Orion Nebula from the center of a large city by simply attaching a filter. -light pollution on your lens.

When used correctly, however, the filter can be a fantastic tool to improve your night shots by countering the problem of light pollution.

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