Photometer
instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum
A photometer is an instrument for measuring photometric quantities such as luminous flux, illuminance, or luminance.
Historically, photometry was done by estimation, comparing the luminous flux of a source with a standard source. By the 19th century, common photometers included Rumford's photometer, which compared the depths of shadows cast by different light sources, and Ritchie's photometer, which relied on equal illumination of surfaces. Another type was based on the extinction of shadows.
Most modern photometers detect light by converting it into an electric current using a photoresistor, photodiode, or photomultiplier. Some models employ photon counting, measuring light by counting individual photons. They are especially useful in areas where the irradiance is low. Photometers have wide-ranging applications including photography, where they determine the correct exposure, and science, where they are used in absorption spectroscopy to calculate the concentration of substances in a solution, infrared spectroscopy to study the structure of substances, and atomic absorption spectroscopy to determine the concentration of metals in a solution.
History
Before electronic light sensitive elements were developed, photometry was done by estimation by the eye. The relative luminous flux of a source was compared with a standard source.
“Photometer” enters the record as instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Crown Archives preserves that source wording while asking what Photometer, instrument and measures can confirm, complicate or overturn.
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This entry incorporates text from “Photometer” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.