the rate of emission of heat from a bounding surface per degree of temperature difference between the surface and surrounding substances (called by Fourier external conductivity).
The property of emitting radiation; possessed by all materials to a varying extent.
Ratio of radiation emitted by a surface to the radiation emitted by a black body at the same temperature under similar conditions. May be expressed as total emissivity (for all wavelengths), spectral emissivity (as a function of wavelength), or goniometric emissivity (as a function of angle).
The ratio of total radiative output from a body per unit time per unit area at a specific temperature and wavelength to that of a black body under the same environmental conditions.
a factor which represents the rate at which a given surface material gives off or emits radiant energy.
an intrinsic property of a material indicating how well it radiates heat.
The relative ability of a surface to radiate heat.
A value between 0 and 1 that represents a ratio between an object and a blackbody. The value represents the surface emitance of that object. For a more detailed explanation of emissivity see IR Papers: Emissivity an overview
The ratio of the radiant energy emitted by a any source to that emitted by a blackbody at the same temperature.
the amount of electromagnetic energy (primarily at wavelengths longer than 1.0 micrometer) that an object emits. For example, the Earth emits longwave radiation primarily in the infrared part of the electromagnetic spectrum, but also in longer microwave wavelengths. The emissivity of an object varies as the fourth power of its absolute temperature.
The ability of an object to radiate and absorb energy from its surroundings measured as a ratio of the actual object emission to the blackbody equivalent emission.
the ratio of radiant energy from a material to that from a blackbody at the same kinetic temperature. Materials may have wavelength-dependent emissivities between 0 and 1.0. (approximately the inverse of reflectance)
This is an efficiency of heat radiation. The higher the efficiency, the more the heat is radiated.
The ratio of emitted radiation from an object to the emitted radiation from a black body at the same frequency (or wavelength) and temperature.
The ratio of the radiation emitted by a surface (sample) to the radiation emitted by a blackbody (standard) at the same temperature and under similar conditions. The emissivity (ratio) can closely approach, but never be unity (1.0) or greater than unity. In summary, the emissivity value describes the reflective and absorptive characteristic of a blackened surface in the infrared wavelengths.
The measure of a surface's ability to emit long-wave infrared radiation.
A measure of the ability of a material to radiate energy. It is expressed as a ratio (decimal) of the radiating ability of a given material to that of a black body. A black body emits radiation at the maximum possible rate at any given temperature, and has an emissivity of 1.0.
The ratio of energy emitted by a material to that which would be emitted by a blackbody at the same temperature.
The ratio of radiation at a given wavelength emitted per unit time and per unit area of a surface to that from a perfect (blackbody) emitter at the same temperature in the same environment.
The ratio of the radiant energy (heat) leaving (being emitted by) a surface to that of a black body at the same temperature and with the same area; expressed as a number between 0 and 1.
Emissivity is a surface characteristic of a material. It is the relative ability of a surface to absorb and emit energy in the form of radiation. Low-emissivity (Low-E) coatings reduce the normally relatively high surface emissivity of the glass. The coatings are mainly transparent over the visible wavelengths but reflect long wave infra-red radiation towards the interior of the building. The result is greatly reduced heat loss.
The relative ability of a material to radiate energy per unit of surface area expressed as a ratio to the radiation rate of an ideal black body of identical area and temperature.
This is a measure of the ability of a surface to emit room temperature radiant heat energy. It is also a measure of the ability of the surface to reflect room radiant energy since, for window systems, the emissivity and the reflectivity of room radiant energy add up to unity. A low emissivity means a high reflectivity of room radiant energy.
The ratio of radiant flux from a body to that from a blackbody at the same kinetic temperature.
The measure of surface's ability to absorb or reflect far- infrared radiation. The lower the emissivity rating, the better the insulating qualities of the window film/glass system.
A term related to temperature measurement using Infrared radiation. Errors in IR measurements can occur based on the color, shape and presence of reflection on the measurement surface. A wide emissivity adjustment should be available on an IR thermometer to allow the user to compensate for these types of errors.
The ability of a material to emit heat. Black iron has high emissivity, while aluminum foil has a low emissivity.
The ratio of energy emitted by an object to the energy emitted by a blackbody at the same temperature. The emissivity of an object depends upon its material and surface texture; a polished metal surface can have an emissivity around 0.2 and a piece of wood can have an emissivity around 0.95.
The ability of a surface to emit radiant energy compared to that of a black body at the same temperature and with the same area (thermodynamics term).
Relating to windows, the ability of the glazing to allow radiation to pass through it.
A property of a material, characterizing its capability to emit electromagnetic radiation as a consequence of its inherent thermal energy.
At a given wavelength the ratio of infrared energy radiated by an object at a given temperature to that emitted by a blackbody at the same temperature The emissivity of a blackbody is unity at all wavelengths.
The ratio of emitted radiation of a surface at a given temperature and wavelength to that of a blackbody at the same wavelength and temperature.
The relative ability of a surface to reflect heat, with emissivity factor ranging from 0.00 to 1.00. Emissivity, U-Factor, and R-Factor are different ways to evaluate insulating values.
Emissivity is a measurement of the thermal signature and characteristics of different materials and surfaces. Anything in nature with a temperature above absolute zero emits energy. Emissivity measurement is represented as a ratio of energy emitted by an object at a given temperature to energy emitted by a blackbody at the same temperature. A blackbody is a perfect radiator with an emissivity of 1. Typical objects have an emissivity of .5 to .98. On the opposite end of the spectrum, a mirror has an emissivity of 0.
A measure of an object's ability to emit long-wave infrared radiation or room temperature radiant heat energy. Emissivity varies from 0 (no emitted infrared) to 1 (100% emitted infrared). The lower the Emissivity, the lower the resultant U-value.
The ratio of the actual amount of electromagnetic radiation emitted by an object to the amount emitted by an ideal blackbody at the same temperature.
Even if the temperature is the same, the amount of a radiated infrared beam differs depending on the material or surface condition of the objects. Emissivity is the ratio of radiant energy of an object using a black body as a reference. The following is an important formula for understanding emissivity.
is a term used to describe a surfaces relative ability to absorb and reradiate heat. A surface with high emissivity will radiate heat faster that a surface with low emissivity. Emissivity is recorded on a scale of 0-1, where 0 would be the perfect white surface reflecting 100% of heat while 1 would be the perfect black surface that absorbs 100% of heat. Standard glass surfaces have an emissivity of 0.84, while low e glass surfaces have emissivity ratings of 0.08 to 0.04.
The ratio of radiant exitance (M) of a surface to the radiant exitance of a blackbody at the same temperature. A blackbody has an emissivity of 1, other objects have emissivities between 0 and 1.
The energy emission rate usually expressed as r/c/hr @ 1ft or mr/mc/hr @ 1 ft.
The efficiency with which a material radiates thermal energy, expressed as a fraction between 0 and 1.
The ability of a material to emit radiant energy. Emittance is the ratio of the total radiant energy emitted by a given surface to that emitted by an ideal black body at the same temperature. To emit is to give out, to discharge-in the case of glass, essentially, to reradiate absorbed energy (heat).
The emissivity of a material (usually written \epsilon) is the ratio of energy radiated by the material to energy radiated by a black body at the same temperature. It is a measure of a material's ability to absorb and radiate energy. A true black body would have an \epsilon=1 while any real object would have \epsilon<1.