The Lumicon Deep-Sky Filter is THE foremost broadband filter efficiently blocking ALL mercury-vapor and high & low pressure sodium-vapor lamp light, neon lights and airglow, while allowing the rest of the visible spectrum through. The superior contrast gain between the object you're viewing and the black background of space allows you to view galaxies, nebula, star clusters, comets, etc. wonderfully -- when observing from light-polluted urban skies -- making it the best all-around visual light pollution filter.
The Lumicon Deep-Sky Filter's high transmission in the H-alpha end of the spectrum makes it THE ONLY premium astrophotographic filter on the market for not only color photographs, but also for black & white photos and CCD work. Lumicon tests every filter individually on a Perkin-Elmer Double-Beam spectrophotometer, inscribing on the filter its % transmission for each of the primary spectral lines.
Do not settle for cheap, foreign-made, low-transmission broadband filters.