Light pollution in astrophotography: The thorn in all of our sides.
- Thomas McCrorie
- May 19
- 5 min read
Updated: Jun 9
Most people don't even consider light polluton at all, it has no direct effect on them. But light pollution has such an dramatic effect not only on nature and what we can't see in our night skies, but it is having a huge effect on nature in general.
Light pollution is often treated like an unfortunate inconvenience. For astrophotographers, it’s a central challenge that shapes every aspect of imaging—from deep sky object selection to processing strategy. It doesn’t just affect the visibility of faint stars and screw up faint nebula and distant galaxies—it alters how we calibrate exposures, what filters we use, and how much detail we can coax from the sky.
Light pollution disrupts the natural rhythms of wildlife and ecosystems. Many animals rely on natural light for navigation, reproduction, and foraging—artificial lighting can confuse these signals, leading to fatal consequences. For example, sea turtle hatchlings may head toward streetlights instead of the ocean, and migrating birds can become disoriented, often colliding with illuminated buildings. Even plants and insects are affected, with altered pollination patterns and disrupted growth cycles. Overall, excessive artificial light disturbs the balance of natural ecosystems and contributes to biodiversity loss.
But understanding it in detail is crucial for the success of your images—especially if you’re not lucky enough to live under pristine Bortle 1 skies.
Types of light pollution and their sources
There are three main types of light pollution that affect astrophotography:
Skyglow – The brightening of the night sky over populated areas caused by scattered light in the atmosphere, making it hard to see stars and celestial objects.
Glare – Excessively bright light that causes visual discomfort or reduces visibility, often from poorly shielded outdoor lighting.
Light Trespass – When unwanted artificial light spills into areas where it’s not needed or intended, such as streetlights shining into bedrooms.
Clutter – The confusing and excessive grouping of bright lights, especially in urban areas, which can distract or disorient both humans and animals.
Over-illumination – Using more light than necessary, often in commercial or residential areas, leading to wasted energy and unnecessary light exposure.
Knowing your local sources of light pollution is the first step. Walk around your local area during imaging hours. Note direct and indirect light. Simple shielding, repositioning, or negotiating with neighbours (gently) can reduce the impact of some sources of light pollution on your astrophotography imaging sessions.
You can find out more about Dark Sky UK here
Bortlescale realities vs. theory
Most astrophotographers and night sky imagers use the Bortle Scale to classify their sky quality, from Class 1 (darkest) to Class 9 (urban core). While useful, it has its limitations:
Bortle 5-6 skies still allow impressive images—if you know how to work within them. Many Picastro users in suburbs produce stunning galaxies and nebulae using narrowband filters and careful processing. But this is no excuse to berrate the effect of light pollution. We still need to try and mitigate it somehow.
Your real limitation isn’t just the Bortle class, but the consistency and sky quality. For example, a Bortle 4 sky with frequent haze and poor atmospheric conditions, can perform worse than a dry Bortle 6.
Use tools like LightPollutionMap.info to evaluate your area. Also, spend a few nights measuring your sky with a Sky Quality Meter (SQM) if possible—it tells a more nuanced story than the Bortle estimate alone.
Filters that actually help
There’s no magic bullet here, but filters are vital. Here’s how to choose the right type:
Broadband Filters (L-Pro, L-Extreme, CLS, IDAS D1 etc)
Great for general use in light-polluted areas. These work best on brighter targets like larger galaxies, star clusters and brighter nebulae.
Narrowband Filters (Ha, OIII, SII)
Transformative for emission nebulae and adding faint Ha to galaxies. These isolate specific wavelengths of light, cutting out almost all background glow. Many astro imagers in Bortle 7+ zones use narrowband exclusively.
Dual/Narrowband for one-shot Colour (OSC) cameras
Filters like the Optolong L-eXtreme work wonders for beginners using OSC. They provide near-monochrome signal separation without needing a full mono rig.
Choose filters that match your target
For instance, imaging the Andromeda Galaxy with an H-alpha filter won’t help—but the same filter will dramatically improve a shot of the Heart and soul nebula. LRGB filters are generally used for imaging galaxies but can be used to image emission nebula and reflection nebula.
Planning around urban environments
Urban settings require strategic planning. Here’s how to adapt to your conditions:
Image high if you can
Aim for targets that rise high above the horizon and shoot as close to zenith as you can to avoid light domes. Use Stellarium or Sky Safari to forecast altitude throughout the night.
Get the timing right
Wait until after midnight during the summer months when darkness is a little better and start shooting after 6.30 during the winter months when businesses shut and some local lighting decreases.
Use physical barriers
Portable light shields and dew shields, tall fences or bushes, or even dark fabric over your rig can block intrusive local light. I foudn this out taht even small silar ligths can have an effect on your lightframes. Cover them up during your imaging session.
Stack more frames
Signal-to-noise ration improves with stacking, and be ruthless when stacking as adding in rubbish can only produce rubbish. Urban astrophotographers often take 3x or 4x the exposures needed at dark sites to compensate for light pollution. An example of this is Clint Shimmer who images from Bortle 9 skies in the US and his images are actually really amazing. You can see his Picastro public profile here.
Keep sessions short and purposeful
Focus on bright targets if you are limted by heavy light pollution and track their position carefully, and you can always stop when gradient levels become unmanageable. Although modern improvements on algorithm based gradient removal tools such as those contained in Pixinsight and other amazing tools from Seti Astro for example are incredible these days. This is not a sollution to helping to combat light pollution though.
Narrowband isn’t a cheat code—but can help
There’s a misconception that narrowband filters magically remove all problems. They help, but not without trade-offs:
Longer Exposures
Narrowband filters reduce the amount of light hitting the sensor, requiring exposures of 300s or more. This can also bring other issues of over exposed and bloated stars depending on the filters being used of course.
Colour balance
OSC (one shoot colour) users may find coloor calibration difficult without a broadband frame to guide white balance.
Processing complexity
You’ll need to learn multi-channel combining (especially with mono cameras), which introduces a steeper learning curve. Therea re some fantastic videos around on yourtube though epxlaining combining all of these processes to produce the best results.
That said, narrowband imaging is one of the most effective tools for urban astrophotographers. The ability to isolate target emissions from background noise is eastro-life-changing—and it opens access to faint nebulae and dark nebula even in the city.
In relation to general astrophotography, light pollution is not a deal-breaker. It’s a creative constraint. Some of the most inspiring images on Picastro come from city balconies, urban rooftops, or garden sheds next to busy motorways. What they share isn’t perfect skies—it’s planning, adaptation, and thoughtful techniques.
Understand your light environment, use the right tools, and you’ll be amazed what can emerge from the skyglow.
Clear skies everyone.
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