emissivity

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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

emissivity

(em-ă-siv -ă-tee) Symbol: ∊. A measure of a body's ability to radiate electromagnetic radiation as compared to that of a perfect radiator – a black body – at the same temperature.

Emissivity

Ratio of radiation a surface gives off. Using products with low emissivity—for example, white roofs rather than black roofs—reduces the heat island effect, whereby urban landscapes become significantly warmer than surrounding rural landscapes.

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.

thermal emissivity

The ratio of the rate of radiant heat energy emitted by a body at a given temperature to the rate of radiant heat energy emitted by a blackbody, 1 at the same temperature, in the same surroundings.
References in periodicals archive ?
For the emissive layers, which must be patterned, the company developed a nozzle printing process that simultaneously prints the red, green, and blue layers.
Meanwhile, emissive efficiency (lm/W) of the phosphorescent type can theoretically become four times that of the fluorescent type.
Blue light, compared to green and red, comes from a higher energy emissive state that naturally places greater demands on the materials in the device.
pLEDs are one class of organic light-emitting diodes, a display technology platform for producing bright, high-contrast, low-voltage emissive displays.
And by 1995, the amount of our chlorine going into emissive uses will be under 5%.
Bluetooth, 4G LTE Multi Carrier (EM7355), Fingerprint, Emissive Backlift Keyboard, Multi-drive, Toughbook Preferred, CF-S09SLC4 - Toughbook Premier Service Level Program, Deployment, Asset Tag, Online Svc Analysis, Asset Management, Disk Image Management and Preferred Handling at NSC (Years 1,2,3 and 4), CF-SVCLTNF4Y- Protection Plus - Laptop (Years 1, 2, 3, and 4).
Developers, manufacturers, graduate students, and engineers in display technology will find eleven chapters addressing the following topics: electronic addressing, CMOS backplane technology, transmission microdisplay structure, transmissive and reflective liquid crystal microdisplays, LCD assembly and testing, micromechanical devices, emissive microdisplays, projection displays, and near-to-eye systems.
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.
Type FB flat quartz infrared heaters and Unitube tubular quartz infrared heaters provide peak efficiencies by matching emissive wavelengths of heating elements to the absorption wavelengths of product (Selective Wavelength Method).
The new panel can reproduce blacker blacks and the details of dark images thanks to its new "Crystal Emissive Layer.
Of the total OLED materials market value, the active OLED materials - emissive materials, hosts, and hole/electron injection and transport materials are expected to account for nearly USD 3 billion.