9 Light Pollution Filters Tested: Do They Really Work?

Light pollution is the bane of Milky Way photographers. The garish yellow, orange, or blue colors that artificial lights cast upon our landscapes and night skies often make processing astrophotography images difficult.

To combat the color imbalance and exposure issues caused by light pollution, numerous filter manufacturers have created “light pollution” filters. B&H Photo has a three-part series of articles where they tested nine light pollution filters. I know this is something many of you (and I) have dreamed of doing, but due to the expense involved with buying that many filters, it’s just on practical. The article is by Todd Vorenkamp.

Light Pollution Basics

Light pollution comes from just a few types of light sources. These are the outdoor lighting in urban and industrial settings. The most common sources are low-pressure sodium, high-pressure sodium, metal halide, and light emitting diodes.

Low-Pressure Sodium

Low-pressure_sodium_lamp_700-350nm.jpg: StarlightCBL derivative work: Jean-Jacques MILAN, Low-pressure sodium lamp 700-350nm widened, marked as public domain, more details on Wikimedia Commons

Light spectra from a Low-Pressure Sodium Lamp. Notice how much brighter the yellow-orange lines are compared to the other colors.
Source: Wikimedia.org

Low-Pressure Sodium (LPS) lights are very energy-efficient at producing light. Since the LPS spectrum is so narrow, it is used in areas surrounding astronomical observatories as it is readily filtered.

High-Pressure Sodium

Spectrum of high pressure sodium lamp. This picture was made by Chris Heilman with a home-made spectroscope. Source= http://en.wikipedia.org

A spectrum from a High-Pressure Sodium lamp. See how many more colors are in this than in the LPS one.
Source: This picture was made by Chris Heilman with a home-made spectroscope. Source: Wikimedia.org

High-Pressure Sodium (HPS) lights are commonly street lighting. It’s still an predominantly an amber color, but the addition of other elements like mercury to the bulb help it produce a broader range of colors.

Metal Halide

Metal Halide lighting spectrum. Source: http://www.illinoislighting.org/lightcolor.html
Metal Halide lighting spectrum. Notice there are fewer gaps in the spectrum than in either the LPS or HPS lights. This gives the metal halide light a more pleasant color.
Source: IllinoisLighting.org

Metal Halide lights have replaced mercury vapor lights over the last few years. Both produce a bluish light, with Metal halide lights producing a near daylight color temperature of 5500K.

Light Emitting Diodes

Out spectrum of a High-Pressure Sodium lamp with a LED lamp. The colors produced by the LED are much richer and harder to filter than the HPS. Source: Lamiot (https://commons.wikimedia.org/wiki/File:Leds_sodium_spectrum.jpeg), "Leds sodium spectrum“, https://creativecommons.org/licenses/by-sa/4.0/legalcode
The output of a High-Pressure Sodium lighting compared with a LED lamp. The higher the peak, the more light is produced for each color. You can see the colors produced by the LED are more abundant and will be harder to filter than the HPS.
Source: Lamiot, “Leds sodium spectrum“, Licenses

Light Emitting Diodes (LED) lights produce the entire spectrum of visible colors at much greater energy efficiency than any other commercial light source. Because of all the advantages over other outdoor lighting options, LEDs are becoming the de facto light for all outdoor uses.

Information on Stopping Light Pollution

For more information on light pollution, check out my article on what you can do to Save Our Night Skies from Light Pollution.

Filtering Light Pollution

Astronomers since before the turn of the twentieth century recognized that light pollution causes problems observing the night sky. To combat this issue, they designed light pollution filters. These filters are glass and either contain chemical elements that absorb various wavelengths of light or have dozens of thin coatings on them that remove the light pollution.

Didymium Glass

Didymium glass has been used since at least the 1970s in landscape photography as a “color enhancing” filter. By filtering out yellow light (and some green as well), it saturates the red and some blue tones in a photograph. It’s a popular filter for fall colors, as it makes autumn leaves appear more vibrant.

Low-Pressure Sodium lamps have two bright yellow lines, so close to each other they often look like one line in spectrums. These yellow lines match well with the filtering properties of didymium glass.

In recent years, didymium filters have been used by Nightscaper and Milky Way photographers, removing the amber light produced by both LPS and HPS lighting.

Didymium Glass – Not a Perfect Solution

A large number of light pollution filters are based on didymium glass formulations. However, didymium glass is not a perfect solution for removing light pollution. LED, metal halide, and HPS lighting to a lesser extent, contain a number of other colors that didymium does not remove so it has little effect on these lights.

The other bad news for didymium glass is that stars contain yellow light. At least the brighter ones usually do. That means a didymium filter will make most stars appear dimmer.

Astronomical Light Pollution Filters

Several types of light pollution filters are available for telescope users. Some of them are thin-film interference filters. Unfortunately none of them are very useful for the Milky Way photographer. In addition, they typically come only in 1.25″ and 2″ diameters for use with telescope eyepieces and astronomy cameras. They are, however, often available as clip-on filters for certain digital cameras where the filter fits right over the camera sensor.

The B&H Test Subjects

Now that we’ve covered the basics of light pollution filters let’s look at the ones used in the B&H comparison. Light pollution filters are available in several form factors. As mentioned above, some are sized so they fit inside a camera body right in front of the sensor while some thread into a telescope eyepiece.

For this test, Todd limited the filters to ones useful for most landscape and Milky Way photographers – over-the-lens filters. I’m not sure about the inclusion of ultraviolet (UV) or infrared (IR) filters in this test. These designs aren’t traditionally considered “light pollution filters” so there doesn’t seem to be any reason to include them. But we’ll see how they perform. The proof is in the pudding.

I’ve sorted the filters based on the design types.

“Control”

No filter was a control.

Ultraviolet (UV) Only filter

Heliopan 77mm UV Filter – A high-quality ultraviolet filter chosen as a “semi-control.” It has a filter factor of 1.

Infrared (IR) filters

Tiffen 77mm T1/2 IR Filter – This filter blocks near-infrared (IR)from 680-800nm. It has a filter factor of 1.41x.

SLR Magic 77mm Image Enhancer Filter – Removes both UV and IR light with a filter factor of 1x.

B+W 77mm UV/IR Cut MRC 486M Filter – Removes both UV and IR with a filter factor of 1x.

Schneider 77mm True-Cut 750 IR Filter – Blocks 50% of IR at 750nm. It has a filter factor of 1x.

Didymium Filters

Ice 77mm Lipo Light Pollution Filter – This filter appears to be didymium glass. It has a filter factor of 1.25x.

Haida 77mm NanoPro MC Clear-Night Filter – This appears to be didymium glass. It has a filter factor of 1.25x.

NiSi 77mm Natural Light Filter – This appears to be didymium glass. It has a filter factor of 1.5-2.8x.

Thin Film Filter

Kenko Astro LPR Type II Filter – This appears to be a thin film interference filter. No filter factor is given for it. Kenko recommends this filter only for 100mm or longer telephoto lenses, which is consistent with a thin-film filter. They say it may cause color shifts at shorter focal lengths.

The Camera Gear

A Fujifilm X-T2 APS-C mirrorless camera was used with lenses covering the range from wide-angle, normal, and telephoto. They chose the following lenses – Samyang 12mm f/2.0 NCS CS, the Fujifilm XF 23mm f/1.4 R, and Fujifilm XF 35mm f/1.4 R, the Fujifilm XF 90mm f/2 R LM WR, and a Nikon AF DC-Nikkor 105mm f/2D. For tracking, an iOptron SkyGuider Pro EQ Camera Mount was used.

The Locations

Several locations were used to test these filters. They picked three locations that gave them a range of light pollution levels.

  • Brooklyn, New York. They shot from a rooftop of what’s probably the most light-polluted city in the world!
  • A small town backyard with a population of more than 20,000 residents.
  • A park in an 8,000 person town outside of the 20,000 person town.

Most all the lenses were used at all three locations. They also included the Moon, stars, a couple planets, and even portions of the Milky Way in several of the photos.

None of these locations come close to being “dark-sky” sites. Numerous locations have buildings or even yard lighting. And clouds make an appearance for some tests.

Color Balance

All test images were captured as RAW files with the camera’s White Balance (WB) set to “Auto”. The tests were then processed using several camera color balance settings. The difference between clips A, B, and C is the color balance to which the video clip is set.

  • Original WB – These are straight out of the camera. A few were tweaked for exposure to take into the effect of each subject’s filter factor.
  • Fluorescent – White balance was adjusted using Lightroom’s Fluorescent Setting.
  • WB Neutralized – A spot in each test image was selected and the white balance neutralized on that spot.
  • Adjusted – The WB, “Presence”, and noise reduction were adjusted in Lightroom on the unfiltered “control sample”. This adjustment was then applied to all the other images.

Observations on the Tests

It’s interesting to see the test subjects with the various filters applied. The following are my observations of the tests.

The Kenko

The Kenko Astro LPR Type II filter definitely performs poorly with the wide angle lenses. That’s not a surprise since it appears to be a thin-film design and those types of filters typically show banding. It does much better with the 105mm lens.

Ghosting of Bright Lights

Check out Test 4 in Part One – the closeup of Jupiter. There appears to be some ghost images of Jupiter with some of the filters. It’s impossible to say if it is related to the filters from these tests. Check out Test 5 which has a brightly light building against the night sky. It definitely shows ghosting from reflections even better than Test 4.

Sharpness

To me, some filters of the filters appear sharper than others.

Milky Way Tests

Definitely check out the clips in Part Three – they are perhaps the closest conditions that most Milky Way photographers experience unless they have access to truly dark skies. The tests there show the Milky Way with each of the tested filters.

Wide-Angles

Test 9 uses the 12mm wide-angle lens. To me, the ICE, Haida, and NiSi do the best job here. The Kenko, because of it design understandably does the worst on this test. The photos with it and the wide-angle lens looks a bit like it was made from a pair of granny glasses found on the sidewalk at the corner of Haight and Ashbury.

Telephotos

Test 12 uses the 105mm lens and this is where the Kenko shines – it seems to bring out some of the natural, warm colors of the Milky Way. Perhaps even accentuating the colors in the nebulae. The Tiffen and especially the Schneider remove the nebula color.

I’m Blue Da Ba De…

The ICE, Haida, and NiSi all tend towards a pleasing blue color. This makes sense, since they remove the complimentary color to blue – yellow. This will shift the color balance to blues. This effect may be pleasing to some people.

All the Videos of All the Filter Tests

Part One (Tests 1 to 5) of this Mega-Comparison shows the tests from the big city. https://www.bhphotovideo.com/explora/photography/hands-on-review/9-light-pollution-filters-tested-do-they-really-work?

Part Two (Tests 6 to 8) is from the small town. Some of these tests used the iOptron SkyGuider Pro EQ Camera Mount. https://www.bhphotovideo.com/explora/photography/hands-on-review/9-light-pollution-filters-tested-do-they-really-work-part-2

Part Three (Tests 9 to 12) is from the park. These tests used the iOptron SkyGuider Pro EQ Camera Mount as well. https://www.bhphotovideo.com/explora/photography/hands-on-review/9-light-pollution-filters-tested-do-they-really-work-part-3

What do You Think?

Have you used a light pollution filter? Are you thinking about getting one, but aren’t sure which to get? Share your thoughts on light pollution filters with us.

I’m planning to get a couple of these filters together so I can compare them myself this summer. Let me know which filters you’re interested in and I’ll see if I can get some for testing.

Resources:

For more information on industrial and commercial lighting, check out the blog at StouchLighting.com

The International Dark-Sky Association has some resources and information on how you can help reduce light pollution.

An excellent resource for telescope astrophotographers is Agena Astro Products. Not only do they sell telescopes and accessories (like light pollution filters), but Agena has excellent reviews and guides on how to use them as well.

Spectra of actual city skies can be found at YourLightPollution.com This is an interesting site with info on how light pollution has changed with time. Numerous spectra from cities in the USA and Canada are shown there. A pdf eBook “Your Light Pollution – The New Sky-Glow Spectra” can be purchased from the site.

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