A polarizer is a type of optical filter which lets the light of a specified polarisation pass through it whilst blocking other polarisations. It converts a beam of light that's of mixed polarisation into a well-defined beam, or polarised light. Polarizers can be made for radio waves, microwaves and arrays too so their applications are not only limited to light and they can be used on other electromagnetic waves too. Polarisers that analyse or create light can be used for sunlight readable touchscreens, stress analysis of glass or plastics, 3D projection systems, photography, contrast enhancement display filters, optical sensors and safety light curtains and Ophthalmology. Polarising filters are used in photography on camera equipment where it removes unwanted and potentially distracting reflections from non-metallic surfaces such as water and glass, and also assists in increasing colour saturation.