Do light pollution filters actually work?

They worked remarkably well against the old sodium street lamps, whose output sat in a few narrow bands. Against modern white LED lighting, which emits across the whole spectrum, there is no narrow band to remove and far less to be gained.

The reputation of these filters was built in a different lighting era, and the honest answer depends on what is outside your window.

Why they worked so well before

High-pressure sodium lamps emit in a few narrow bands. A filter that blocked those bands removed most of the sky glow while passing almost everything astronomical, which is close to a free improvement.

What LED changed

White LEDs emit a broad continuum. There is no narrow band to remove, and a filter that removes enough of the continuum to darken the sky removes the object along with it. A maker who publishes a transmission curve is telling you something; one who publishes a claim is not.

What still works

Emission objects. A nebula radiating at discrete wavelengths still stands out when the continuum is suppressed, so the filters marketed for nebulae remain useful under any lighting. Galaxies and star clusters do not benefit, whatever the packaging says.

Before buying

Find out what the street lights near you actually are. The same filter transforms a sodium-lit sky and does very little under white LED, and no review can answer that question for your street.

If this page and the manufacturer’s own documentation disagree, follow the documentation. Every aperture, focal length, payload rating, field, eye relief, transmission figure and thread size on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any filter: the name is not the bandpass. Two filters sold under the same three letters can pass windows of very different width, and the figure that decides what a filter does is the transmission at the emission lines together with the width of the window. This page reports the band and the percentage where a maker publishes them, and says they are missing when they are not.