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emissivity |
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emissivity [‚ē·mə′siv·əd·ē] (thermodynamics) The ratio of the radiation emitted by a surface to the radiation emitted by a perfect blackbody radiator at the same temperature. Also known as thermal emissivity. Emissivity The ratio of the radiation intensity of a nonblack body to the radiation intensity of a blackbody. This ratio, which is usually designated by the Greek letter ε, is always less than or just equal to one. The emissivity characterizes the radiation or absorption quality of nonblack bodies. Published values are readily available for most substances. Emissivities vary with temperature and also vary throughout the spectrum. For an extended discussion of blackbody radiation and related information See Heat radiation. A spectral emissivity of zero means that the heat radiator emits no radiation at this wavelength. Strongly selective radiators, such as insulators or ceramics, have spectral emissivities close to 1 in some parts of the spectrum, and close to zero in other parts. Carbon has a high spectral emissivity throughout the visible and infrared spectrum, exceeding 0.90 in certain portions; thus carbon is a good blackbody radiator. Tantalum is the only metal with a spectral emissivity greater than 0.5 in the visible spectrum. All other metals have a lower spectral emissivity. Tungsten is a relatively good emitter, with a spectral emissivity of 0.43–0.47 within the visible region of the spectrum. See Blackbody How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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| While fluorescent organic EL devices are already available on the market for mobile phone display applications, phosphorescent organic EL devices, which are yet to be commercialized, can theoretically produce four times higher emissive efficiency, resulting in about one-fourth electricity consumption. In accordance with current terminology, the conspicuousness [zametnost] of a model of arms or military equipment is defined as an aggregate contrast between its reflective and (or) emissive characteristics on the one hand, and the background, on the other, making it possible to detect and identify a particular target and aim a weapon system on it. The Army seeks to provide the innovative research and development for materials, devices, and manufacturing processes to solve critical challenges in the performance and fabrication of emissive, transmissive, and reflective flexible display technologies. |
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