Lighting can be enhanced in ways that go beyond what exists in nature.  Star filters create points of light, like ""stars,"" streaking outward from a central light source.  This can make lighting within the scene take on a more glittering, glamorous appearance.  This effect is produced by a series of thin lines etched into the flat optical surface of a clear filter.  These lines act as cylindrical lenses, diffracting light points into long thin lines of light running perpendicular to the etched lines.  Lines on the filter positioned horizontally produce vertically oriented star lines.

Star filters turn point light sources and specular highlights into stars. Commonly seen star filters can generate four to sixteen points stars. A star filter consists of two glasses. The top one is rotatable and has a grid etched into the glass surface.  More precisely, the wider the distance, the fewer number of stars. This distance can be 1mm to 4mm. The 2mm version is the most common one. Some star filters can even create variable star shapes. That is, in the case of 4-point star, the two etched lines do not have to be perpendicular to each other, and can be rotated to form any desired angle.