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Definition: photometry from Dictionary of Energy

Measurement. the measurement of the visible portion of radiant energy (light). Compare radiometry.

photometry

From The Columbia Encyclopedia
(fōtŏm'Әtrē), branch of physics dealing with the measurement of the intensity of a source of light, such as an electric lamp, and with the intensity of light such a source may cast on a surface area. The intensity of electric lights is commonly given as so many candlepower, i.e., so many times the intensity of a standard candle. Since an ordinary candle is not a sufficiently accurate standard, the unit of intensity has been defined in various ways. It was originally defined as the luminous intensity in a horizontal direction of a candle of specified size burning at a specified rate. Later the international candle was taken as a standard; not actually a candle, it is defined in terms of the luminous intensity of a specified array of carbon-filament lamps. In 1948 a new candle, about 1.9% smaller than the former unit, was adopted. It is defined as 1/60 of the intensity of one square centimeter of a blackbody radiator at the temperature at which platinum solidifies (2,046 degrees Kelvin). …
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Full text Article photometry

From The Penguin Dictionary of Physics
photometry Lummer-Brodhun photometer
Photometry is concerned with measurements of light intensity and amounts of illumination. Two types of measurement are possible. In one, the radiation is evaluated according to its visual effects, i.e. according to judgment by observers ( see LUMINOSITY ; LUMINOUS EFFICIENCY ). The physical…
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Full text Article photometry

From Collins Dictionary of Astronomy
The measurement of the brightness or intensity of a source of light or other electromagnetic radiation. In astronomy, photometric measurements are taken over particular ranges of frequency or wavelength (these ranges are called wavebands) and take account of how brightness varies with both waveband…
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Ptolemy's Almagest of about 150 AD is the earliest known star catalogue to contain the brightness or magnitude of stars. The magnitudes were specified on a 1 to 6 scale, with 6 being for the faintest visible stars. No significant revision was made to Ptolemy's catalogue for eight hundred years, when…
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Full text Article photometry

From The Columbia Encyclopedia
(fōtŏm'Әtrē), branch of physics dealing with the measurement of the intensity of a source of light, such as an electric lamp, and with the intensity of light such a source may cast on a surface area. The intensity of electric lights is commonly given as so many candlepower, i.e., so many times the…
| 694 words
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Full text Article photometry

From Britannica Concise Encyclopedia
Precision measurement of the brightness, colour, and spectrum of star s and other celestial objects to obtain data on their structure, temperature, and composition. About 130 bc Hipparchus used a system that divided the stars into six magnitude s, from brightest to faintest. Beginning in the 17th…
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British astronomer William Huggins (1824–1910) was one of the first people to use photographs in astronomy. He used photographic plates exposed over a long period of time—minutes or hours—to record images. Huggins also showed how photographic emulsions could be mixed to increase sensitivity to…
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Full text Article photometry

From The American Heritage(R) Dictionary of the English Language
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Full text Article photometry

From The Penguin Dictionary of Psychology
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Full text Article UBV photometry

From The American Heritage(R) Dictionary of the English Language
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Full text Article photographic photometry

From Collins Dictionary of Astronomy
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