In addition to air turbulence, light pollution is the largest obstacle to observing light objects beyond our solar system. Artificial light in human settlements means the skies are no longer truly black. This negatively affects contrast and, resultantly, detection of deep sky objects.
Depending on the type of celestial object, part of the light pollution can be filtered out, making it easier to observe the object. A CLS filter is a good all-rounder for use in this area. It takes advantage of the fact that light pollution is not equally distributed across the entire spectrum. These colours - especially typical streetlight colours - are suppressed whilst light from deep sky objects is still allowed through.
A must-have for every visual observer.
