This page describes the use of lenses and filters to manage the properties of light within a system. Common applications could include machine vision, color sensing, or laser direction.
Lenses and filters manage the properties of light which passes through them. By selectively allowing light to pass through, filters can control color, light polarity and brightness. In this respect, a liquid-cristal display is simply a programmable filter.
Lenses are used to bend light into a new path. They use material density changes and curveatures to bend incoming or outgoing light into the desired path, either converging or diverging the beam.
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Filters generally absorb or reflect light of certain wavelengths (or within a certain range of wavelengths), while allowing all other light to pass. This is often achieved by doping the glass or polymer lens with organic and inorganic compounds which absorb light or by applying coatings to a glass or polymer substrate which reflect light of certain wavelength ranges. Some filters are built to attenuate specific wavelengths or to pass only certain wavelengths. Such filters can also be applied to wavelength ranges outside of the visible range, into the infrared (IR) or ultraviolet (UV) ranges. The dark plastic cases of some photodiodes or phototransistors are actually transparent in the infrared range, allowing them to send or receive infrared light without being affected by ambient visible light sources.