A night filter is a photographic filter designed for night photography, especially in cities and other areas with a high degree of artificial lighting. Its main purpose is to reduce so-called light pollution, which is an undesirable yellow to orange color cast in images, primarily caused by sodium vapor lamps in streetlights. The filter selectively blocks light wavelengths typical of these sources but allows other parts of the color spectrum to pass through. The result is a photograph with more natural color rendition, a darker and more neutral sky, better contrast, and clearer stars. It is often also referred to as a "natural night" filter or an anti-light pollution filter.