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Hefner Lamp
The Hefner lamp, or in German ''Hefnerkerze'', is a flame lamp used in photometry that burns amyl acetate. The lamp was invented by Friedrich von Hefner-Alteneck in 1884 and he proposed its use as a standard flame for photometric purposes with a luminous intensity unit of the Hefnerkerze (HK). The lamp was specified as having a 40 mm flame height and an 8 mm diameter wick. The Hefner lamp provided the German, Austrian, and Scandinavian standard for luminosity during the late nineteenth and early twentieth centuries. The unit of light intensity was defined as that produced by the lamp burning amyl acetate with a 40 mm flame height. The light unit was adopted by the German gas industry in 1890 and known as the ''Hefnereinheit''. In 1897 it was also adopted by the Association of German Electrical Engineers under the name ''Hefnerkerze'' (HK). Germany moved to using the new candle (NC) from 1 July 1942 and the candela (cd) from 1948. :1 Hefnerkerze is about 0.920 cand ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power. In modern photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Typically, this weighting function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way. Photometry and the eye The human eye is not equally sensitive to all wavelengths of visible light. Photometry attempts to account for this by weighting the measured power at each wavelength with a factor that represents how sensitive the eye is at that wavelength. The standardized model of the eye's response to light as a function of wavelength is given by the luminosity function. The eye has different responses as a function of wavelength when it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amyl Acetate
Amyl acetate (pentyl acetate) is an organic compound and an ester with the chemical formula CH3COO H2sub>4CH3 and the molecular weight 130.19g/mol. It is colorless and has a scent similar to bananas and apples. The compound is the condensation product of acetic acid and 1-pentanol. However, esters formed from other pentanol isomers (amyl alcohols), or mixtures of pentanols, are often referred to as amyl acetate. The symptoms of exposure to amyl acetate in humans are dermatitis, central nervous system depression, narcosis and irritation to the eyes and nose. Uses It is used as a flavoring agent, as a paint and lacquer solvent, and in the preparation of penicillin. It is an inactive ingredient in liquid bandages. It is used as a fuel in the Hefner lamp. See also *Isoamyl acetate, also known as banana oil. *Ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friedrich Von Hefner-Alteneck
Friedrich Heinrich Philipp Franz von Hefner-Alteneck (April 27, 1845 in Aschaffenburg – January 6, 1904 in Biesdorf near Berlin) was a German electrical engineer and one of the closest aides of Werner von Siemens. He is largely remembered for the invention of the Hefner lamp, which provided the measure of luminous intensity used in Germany, Austria and Scandinavia from 1890 to 1942. The measure was called the ''Hefnerkerze'' (HK). The Hefnerkerze was superseded in the 1940s by the modern SI unit, the candela. He was elected a member of the Royal Swedish Academy of Sciences in 1896. Notable Inventions von Hefner-Alteneck's most notable inventions were all conceptualized during his time at Siemens. * Differential arc lamp - A type of automatic-feed carbon arc lamp * Drum armature - An efficient form of winding motor rotor coils * A telegraph keyboard * The Hefner lamp Gallery File:Hefnerlampe.png, Hefner lamp The Hefner lamp, or in German ''Hefnerkerze'', is a flame lam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luminous Intensity
In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit. Measurement Photometry deals with the measurement of visible light as perceived by human eyes. The human eye can only see light in the visible spectrum and has different sensitivities to light of different wavelengths within the spectrum. When adapted for bright conditions (photopic vision), the eye is most sensitive to yellow-green light at 555 nm. Light with the same radiant intensity at other wavelengths has a lower luminous intensity. The curve which measures the response of the human eye to light is a defined standard, known as the luminosity function. This curve, denoted ''V''(λ) or \textstyle \overline(\lambda), is based on an average of widely ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Candela
The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous to radiant intensity, but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the standard luminosity function (a model of the sensitivity of the human eye to different wavelengths). A common wax candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured. The word ''candela'' is Latin for ''candle''. The old name "candle" is still sometimes used, as in ''foot-candle'' and the modern definition of ''candlepower''. Definition The 26th General Conference on Weights and Measures (C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Candlepower
Candlepower (abbreviated as cp or CP) is a unit of measurement for luminous intensity. It expresses levels of light intensity relative to the light emitted by a candle of specific size and constituents. The historical candlepower is equal to 0.981 candelas. In modern usage, ''candlepower'' is sometimes used as a synonym for ''candela''. History The term candlepower was originally defined in the United Kingdom, by the Metropolitan Gas Act 1860, as the light produced by a pure spermaceti candle that weighs and burns at a rate of . Spermaceti is a material from the heads of sperm whales, and was once used to make high-quality candles. At the time the UK established candlepower as a unit, the French standard of light was based on the illumination from a Carcel burner. They defined the unit was that illumination that emanates from a lamp burning pure colza oil (obtained from the seed of the plant '' Brassica campestris'') at a defined rate. Ten standard candles equaled about one Car ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Obsolete Units Of Measurement
This is a list of obsolete units of measurement, organized by type. These units of measurement are typically no longer used, though some may be in limited use in various regions. For units of measurement that are unusual but not necessarily obsolete, see List of unusual units of measurement. For units of measurement that are humorous in nature, see List of humorous units of measurement. Area * Antsingae – a unit of area, smaller than the bunarium. * Bunarium (plural "bunaria") – a unit of area, equal to about 120 ares or 12,000 square metres * Carucate * Cawnie * Decimal * Dessiatin * Ground * Hide * Juchart * Jugerum * Katha * Lessa or Lecha * Marabba * Morgen * Oxgang * Pari – a unit of area equal to about 1 hectare * Quinaria * Tathe * Virgate Energy, etc. * Poncelet – unit of power * Sthène – unit of force * Technical atmosphere – a unit of pressure Length * Ald * Alen * Aṅgula * Arabic mile * Arş and Arşın – two Turkish units of leng ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photometry
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Photometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an astronomical object's electromagnetic radiation * Spectrophotometry, the measurement of spectral distribution along with the flux or intensity * A photometric study, sometimes also referred to as a lighting "layout" or "point by point" * Photometric stereo, a computer vision technique for estimating 3D shape from one or more images. See also * Photogrammetry * Radiometry Radiometry is a set of techniques for measurement, measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power (physics), power in space, as opposed to phot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
