PureNight FAQ

Lonely Speck PureNight Light Pollution Reduction Filter

PureNight Frequently Asked Questions

Below are the most frequently asked questions for the PureNight Light Pollution Reduction Filter by Lonely Speck. If you have a question not covered here, please ask in the comments section at the bottom of this page or contact us directly.

How do I care for my PureNight filter?

PureNight should only be cleaned with a clean microfiber cloth and a lens cleaning solution safe for coated optical glass. We recommend Zeiss Lens Cleaner.

Please note: We do NOT recommend use of lens cleaning solution on the SharpStar, as it will damage it.

Where can I order?

The PureNight light pollution filter is sold exclusively on lonelyspeck.com by Ian Norman and Diana Southern, creators and owners of the Lonely Speck blog and the PureNight filter. Any other website or store selling a light pollution filter under the PureNight or any other name is not an authorized seller of Lonely Speck’s light pollution filter, and the product being sold is not manufactured or sold by Lonely Speck or covered by the Lonely Speck 100% satisfaction guarantee. For any questions about unauthorized sales of the PureNight filter, please email [email protected].

The PureNight filter can be purchased only through the Lonely Speck website.

How can PureNight improve my night photography?

PureNight will improve the colors and contrast of an image taken in any location impacted by light pollution.

You cannot achieve the same level of improvements with post-processing.

Why is light pollution a problem and how does PureNight help?

Light pollution is a problem that astrophotographers face across the world. Sodium vapor lamps are very commonly used in industrial and street lighting, and light pollution from these lamps can be visible in photos from a hundred miles away.

Even dark sky destinations are impacted by light pollution, as shown in the photo below of Tekapo, New Zealand.

The PureNight is made of didymium glass, which filters out sodium light to give the photographer an image vastly less impacted by any surrounding light pollution.

lonely-speck-pure-night-light-pollution-filter-example-no-filter-2020 lonely-speck-pure-night-light-pollution-filter-example-with-filter-2020

In what situations will PureNight make a difference?

The PureNight will make a noticeable improvement in the quality of your night sky images in any location with a city, town, or other source of light pollution influencing your image.

In today’s world, places without any influence of light pollution are few and far between.  In the U.S. light pollution affects even the darkest skies, including national parks located many miles from the nearest artificial light source. Even under the extremely dark skies of Death Valley, California, light pollution is still present and will impact your photography.

In downtown city skies, the PureNight won’t magically reveal the Milky Way, but it will filter out the ugly orange tinge of sodium lamps for more natural looking urban nightscapes.

How does the PureNight filter work?

PureNight blocks the transmission of yellow-orange light between about 575nm and 600nm wavelengths, the same wavelength as sodium vapor lamps.

In the example above with the PureNight installed, notice the drastic intensity change in the yellow-orange lights of the town, resulting in a more pleasant night sky image.

Below is a transmission curve of the PureNight.


What kind of improvements can I expect from the PureNight?

The benefits of PureNight extend beyond the noticeable improvement in the colors of the image.

The biggest advantage of the PureNight is an increase in contrast in light polluted areas. Light pollution reduces contrast by illuminating moisture and particles in the air. Filtering out this light makes the surrounding sky darker. An example of this improvement can be made by making a comparison between a filtered and non-filtered image and adjusting them in post processing to match in both white balance and exposure.

lonely-speck-pure-night-light-pollution-reduction-filter-los-angeles-suburb-no-filter lonely-speck-pure-night-light-pollution-reduction-filter-los-angeles-suburb-with-filter

The difference is subtle but most noticeable around the galactic center. If we take a closer, 100% magnified look at the galactic center, we can see that the image made with the PureNight retains more of the subtle reds and pinks of the nebulae and shows higher contrast around the galactic center:

pure-night-white-balanced-no-filter pure-night-white-balanced-after

The PureNight has a filter factor of about 1.5, meaning that there will be a reduction in light transmission of the image by about -0.6EV, depending on the amount of light pollution in the scene. To get a better idea of what to expect, feel free to download our sample photos in RAW DNG here. (95.6MB, .zip)

How does PureNight differ from a Red Intensifier like the Hoya Intensifier?

We love the Hoya Red Intensifier. It’s certainly an affordable didymium filter option that we recommend. Limited availability of the Hoya Intensifier and the lack of a square version led us to pursue the design of the PureNight. We use an improved filtration glass with stronger filtration properties than the Hoya Intensifier.

PureNight is available for square filter systems (85mm, 100mm and 150mm sizes). This allows photographers to use a single filter system across their lens collection.

The final improvement: the Hoya Intensifier is made of uncoated or single coated glass which is drastically worse in flare-inducing conditions (e.g. if there is a bright light source against a dark background).  To improve upon this shortcoming, PureNight is multi-coated for highly anti-reflective properties that greatly improve contrast and reduce flare.

Which filter holder do you recommend?

To mount a PureNight you will need:

  • an appropriately sized square filter holder system
  • a system-compatible adapter ring, sized for your lens filter thread diameter


To determine which size filter holder system (85mm,  100mm, or 150mm) and which adapter ring you will need, you will need to know your lens’s filter thread diameter. The filter thread diameter is usually marked in millimeters on the front of your lens with a diameter (⌀) symbol like this:


In this example, the lens shown has a filter diameter of 49mm. Depending on your lens’s filter diameter size, we recommend the following systems. (In general, pick the system size that’s larger than the thread diameter of your lens).

If you don’t already have a filter system, here are some recommendations:

85mm (lenses up to filter diameter of 77mm):

Formatt Hitech 85mm Aluminum Holder (Amazon / B&H) and Formatt Hitech Adapter Rings for 85mm Aluminum Holder (Amazon / B&H)

100mm (lenses up to filter diameter of 105mm):

Formatt Hitech 100mm Aluminum Modular Holder (Amazon / B&H) and Formatt Hitech Adapter Rings for 100mm Holder (Amazon / B&H)

150mm  (certain wide angle lenses with fixed hoods):

Haida 150mm Filter Holder (Amazon / B&H)
Lee SW150 Filter Holder (Amazon / B&H)
NiSi 150mm Filter Holder (Amazon / B&H)

Do you ship outside the USA?

Yes, we ship internationally.

Shipping fees vary by country.

Our international orders are shipped via USPS first-class mail and usually take at least 7-14 business days to arrive. Tracking may or may not be available depending on the international destination. As the buyer, you are responsible for any import taxes (VAT, etc.), duties and custom fees that your country may impose at the time of receipt of the shipment.

All international shipments are marked on the customs form as “Merchandise” with an accurate description of the value and contents (“Photographic Filter”) and labeled with the proper six digit HS Tariff Code for photographic filters: 900220. Please check with your local postal service for status updates on your order once it has left the USA.

What if my question isn’t answered here?

For further questions, just ask in the comments below or contact us directly.

54 Replies to “PureNight FAQ”

  1. 1) Will the filter be shipped by USPS or by common carrier (fedex, dhl, etc.)?

    2) If by USPS, can it be mailed to a Post Office Box? I don’t have anything important sent to the street address.


  2. Hey this filter looks potentially very useful for some of my projects. Can you confirm approximately what % of light is passed through the filter at 557.7 nm? From the transmittance chart it looks like there’s a narrow spike of higher transmittance in roughly that area such the green aurora would pass, but the chart isn’t quite granular enough for me to judge for sure. More info on this would be appreciated! Thanks!

  3. I have the 100mm purenite filter & the lee filter holder system. I just got a new lens – sigma 14mm f/1.8 art lens. This lens requires the 150mm setup in order to add any filter to the front of the lens. It does take a rear drop-in filter as part of an adapter to use the lens on the canon eos r.
    My question, would it be possible to make the purenite filter to fit such a rear drop in filter? If so, are there any plans to do so?

    1. The rear holder for the Sigma 14mm f/1.8 is unfortunately only for very thin, flexible gel (plastic sheet) filters which makes it unsuitable for glass filters like the PureNight.

  4. Have you done any testing around portable LED lighting towers, the application I’m looking to use it in has about 97% LED light, 3% irradessent light.

    1. The result would highly depend on the spectrum of the LED lights. Many LED lights cover a much broader band of the visible spectrum than is filtered by the PureNight.

  5. I am new to astrophotography. What advantage would this filter provide versus changing the color balance to more of a blue?

    1. The PureNight targets yellow-orange tones directly, rather than affecting all colors as a color balance adjustment would. By directly eliminating the light pollution, the filter also increases contrast among the colors that remain in the night sky.

    1. Brian E, this is what I am currently using and it works very, very well. I’ve had no issues at all.

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