Light Pollution Solutions: Filters & Techniques for Urban Astronomers

Before you can fight light pollution, you need to understand what you're fighting.

Types of Light Pollution:

• Skyglow — The dome of light over cities visible from miles away
• Glare — Direct bright sources in your field of view
• Light Trespass — Neighbors' lights shining into your space
• Over-illumination — Simply too much light for the area

The Science: Most artificial lighting uses specific wavelengths. Sodium vapor produces a telltale orange. LEDs produce broad spectrum with blue peaks. Nebula filters exploit gaps in this spectrum where natural objects emit light but artificial sources don't.

Check your Bortle class on our Dark Sky Map to understand your starting point.

Astronomical filters block light pollution wavelengths while passing wavelengths from celestial objects.

Light Pollution Filters (Broadband):

• Block sodium and mercury vapor wavelengths
• Slightly improve contrast in suburban skies
• Work on all objects (stars, planets, DSOs)
• Examples: Orion SkyGlow, Lumicon Deep Sky

Narrowband Filters:

• Block everything except specific nebula emission lines
• Dramatic improvement on emission nebulae
• Useless for stars, galaxies, planets
• Examples: UHC (Ultra High Contrast), OIII, H-alpha

Line Filters:

• Ultra-narrow pass at single wavelength
• Maximum contrast on specific targets
• Very dark, requires large aperture
• Examples: 7nm or 3nm H-alpha, OIII

For Nebulae (Emission): The UHC filter is the urban astronomer's best friend. It passes OIII (500nm) and H-beta (486nm) wavelengths while blocking nearly everything else.

Results:

• Orion Nebula: Dramatically improved structure
• Veil Nebula: Visible from suburban sites
• Ring Nebula: Pops against sky background

For Planetary Nebulae: OIII filters make planetary nebulae visible where they'd otherwise be impossible. The Blinking Planetary, Eskimo Nebula, and Cat's Eye all benefit.

For Planets: Light pollution filters don't help planets much—they're bright enough already. But colored filters (blue, green, yellow, red) can enhance specific features:

• Blue: Jupiter's cloud bands
• Red: Mars surface features
• Yellow: Saturn's rings

For Galaxies and Star Clusters: Sadly, no filter helps here. Galaxies and clusters emit broad-spectrum light, so any filter that blocks light pollution also blocks your target. Better to chase darker sites for these objects.

Imagers have more options than visual observers because cameras can handle very narrow filters.

Broadband (One-Shot Color Cameras):

• Light pollution filters help but can't eliminate color casts
• Best for widefield Milky Way shots from suburbs
• Examples: Optolong L-Pro, IDAS LPS-D2

Narrowband (CCD/CMOS Monochrome):

• Complete immunity to light pollution
• Shoot through full moon or city glow
• Requires monochrome camera and filter wheel
• H-alpha, OIII, SII filters for Hubble palette

Duo-Narrowband (One-Shot Color):

• Passes H-alpha AND OIII simultaneously
• Works with color cameras
• Great balance of convenience and LP rejection
• Examples: Optolong L-eXtreme, Antlia ALP-T

For serious urban astrophotography, nothing beats narrowband. I've shot 8-hour exposures from my backyard next to streetlights with zero LP impact.

Filters aren't the only solution. Strategic observing can dramatically improve your experience:

Object Selection

• Focus on bright targets: planets, Moon, double stars
• Emission nebulae visible under LP: Orion, Swan, Lagoon
• Globular clusters punch through LP well
• Save galaxies for dark sky trips

Timing

• Observe when targets are highest (least atmosphere)
• After midnight, many lights turn off
• Winter = longer nights, often clearer skies
• Target objects away from light domes on horizon

Site Optimization

• Shield direct light sources with buildings, fences
• Let eyes fully adapt (30 minutes minimum)
• Use only red light
• Sit with your back to the brightest direction

Equipment Tricks

• Higher magnification darkens background, improves contrast
• Larger aperture gathers more light, overpowers LP
• Cooled cameras reduce noise for longer exposures

Check conditions on our Dashboard — transparency and seeing matter even from urban sites.

The best filter is... less light pollution. You can make a difference:

At Home:

• Install motion sensors on outdoor lights
• Use shielded fixtures that point down
• Choose warm (2700K or lower) bulbs
• Turn off unnecessary lights at night

In Your Community:

• Attend city council meetings about lighting ordinances
• Educate neighbors about light trespass
• Advocate for dark-sky compliant streetlights
• Join the International Dark-Sky Association

Dark Sky Places:

• Support designated Dark Sky Parks and Reserves
• Visit them! Tourism dollars = conservation funding
• Report violations of lighting codes

The Business Case:

• Shielded lighting saves energy
• LEDs have long payback periods
• Dark sky tourism brings revenue

Every fixture you improve helps all astronomers in your area. Check our Dark Sky Map to see how your region compares globally—and what could be improved.

Here are my go-to targets for Bortle 6-8 skies:

No Filter Needed:

With UHC Filter:

With OIII Filter:

Don't let light pollution stop you. Get out there tonight! 🔭