Absorption A physical phenomenon in which a part of radiant energy falling on a body is absorbed by the body.
Related terms: Light absorption, Heat absorption, Absorbing coating, Absorbing layer, Absorbing surface, Light absorbing (absorbing light), non-fluorescent.
Absorbance (Absorptance) A measure of the ability of a body to absorb the incident radiant energy. Quantitatively, absorbance usually designated as α , is defined as the ratio of radiant energy absorbed by the body to incident radiant energy.
Absorptivity (1) same as absorbance;(2) ability of a body to absorb incident light.
Related terms: High absorptivity, High absorptivity coating, High absorptivity layer
Absorber platean element of solar collector which is intended for the absorption of solar radiation.
Related terms: Absorber plate surface, Selective absorber plate, Absorbent layer
Aluminum electrolytic capacitora type of capacitor consisting of a metallic foil (anode) , applied on it metal oxide layer (insulator) and a liquid electrolyte in contact with a second metallic foil, both acting as cathode. Related terms: Aluminium electrolytic capacitor, Electrolytic capacitor, Aluminum foil, Cathode foil, Anode foil, Low-voltage rating, Low-voltage capacitor, Low-voltage electrolytic capacitor, Low impedance, Low ESR, High capacitance, High surface area
Antireflection coating (AR coating)an optical coating which reduces undesirable reflections from surfaces. The following types of antireflection coatings are known: broadband single-layer coatings, broadband multilayer dielectric coatings, and V-coatings (narrowband multilayer dielectric coatings).
Related terms: Antireflective coating, Antiglare coating, Reducing glare, Glare reduction



a perfect emitter and absorber of thermal radiation, there-fore, both its absorbance α and emittance ε are equal to 1.

Related terms: Surface blackening, Blackbody radiation, Blackbody emittance, Black coating, Black chromium, Black layer, Martin Black, Optically black, Optically black coating, Optically black surface, Absorbent pigments, Nextel
Black Matrixa light-shielding film that separates every pixel in a liquid crystal display preventing light from leaking between pixels, and thus improves contrast.
Related terms: Black matrix tubes
Black flock paperRelated terms: adhesive backed flocked paper


Charge-coupled device (CCD)
an image sensor, consisting of an integrated circuit containing an array of sensitive to light capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to at least one of its neighbors. CCDs are used in digital photography and astronomy (particularly in photometry, optical and UV spectroscopy).

Related terms: Digital imaging , Charge coupled device cameras, CCD cameras, CCD sensor, CCD image sensor, CCD laser displacement sensor
Coatinga covering that is applied to an object to protect it or change its surface properties, or appearance. Coatings may be applied in thin layers, for example, by a vacuum deposition technique, such as physical vapor deposition, chemical vapor deposition, etc.

Related terms: Thin coating, Thin layer, Optical coating, High surface area coating
CVCM (collected volatile condensable material)a quantity of outgassed matter from a test specimen that condenses on a collector maintained at a specific constant temperature for a specified time. CVCM is expressed as a percentage of the initial specimen mass and is calculated from the condensate mass determined from the difference in mass of the collector plate before and after the test.

Related terms: TML and CVCM test


Diffuse reflectancea fraction of the incident flux reradiated by diffuse reflection (from a Lambertian surface). Diffuse reflectance measurements are typically used to analyze rough-surfaced solid samples.

Related terms: Diffusive reflectance, Total reflectance, Attenuated total reflectance (ATR)


Emissiona physical phenomenon in which a radiant energy is emitted by the body.

Related terms: Thermal emission, High emission, High thermal emission, High emission coating, High emission surface, High emission layer, High emission surface layer, High emission surface coating
Emittancea measure of the ability of a body to emit the radiant energy. Emittance, usually designated as ε , is quantitatively defined as the ratio of radiant energy emitted by the real body to the radiant energy which a blackbody would emit at the same temperature.

Related terms: Selective emittance, High emittance, High emittance coating, High emittance surface, High emittance layer, High emittance surface layer, High emittance surface coating, Low infrared emittance
Emissivity(1) same as emittance; (2) ability of a body to emit the radiant energy

Related terms: Emissivity signature, Thermal emissivity, Selective emissivity, Low-emissivity window, Low E-window, High emissivity, High emissivity coating, High emissivity surface


Focal-plane array (FPA)
a two-dimensional array of detectors placed in the focal plane of a lens and used to obtain Fourier transforms of image of a light emitting object .

Related terms: Focal plane array imaging system, FPA imaging system, Infrared focal plane array (IRFPA), Cooled IRFPA, Uncooled staring IRFPA,Visible light focal-plane array, Visible light FPA, Focal plane array for visible imaging, FPA for visible imaging, Focal plane array for near infrared imaging
Forward looking infrared camera (FLIR camera )
a camera that takes pictures using the infrared portion of the electromagnetic spectrum. In Europe, these are typically called thermal imagers. Often these contain sub-systems known as thermal imaging common modules or TICM. FLIRs are often described as “infrared cameras“.

Related terms: FLIR system, FLIR imager, Thermal imager, Thermal imaging common module (TICM), Digital image processing


Grazing angle

an angle between a beam incident on a surface and the surface. This term is typically used instead of the term incident angle, when dealing with beams that are nearly parallel to a surface (incident angle is not less than 75°).
Grazing angle reflectiona reflection at a grazing incident angle. Grazing angle reflectance measurements are mostly used for analyzing sub-micron thick films deposited on reflective substrates.

an object having a value of emittance less than 1, but this value is constant at all wavelengths (over that part of the spectrum where the measurement takes place).


Heat shielda barrier that prevents the overheating of a an object by absorbing, reflecting, or dissipating external heat.

Related terms: Heat shield insulation, Spacecraft, Missile, Cold shield
Hemispherical emittancean emittance of a body averaged over all the radial directions of the over-spreading hemisphere.

Hemispherical reflectance
a reflectance of a body averaged over all the radial directions of the over-spreading hemisphere. Hemispherical reflectance is measured for a specified value of the incident angle.

High-reflection coating (HR coating)
a coating which reflects 99%, or more of the light falling on it

Related terms: High-reflective coating, High-reflectance coating


Ideal solar selective surface (coating)
a surface with absolute (100%) absorbance (and emittance) of EM waves, which are shorter than 3 microns ,and zero absorbance (emittance) for the rest of the waves , if T=400°K.

Related terms: Ideal selective surface, Ideal selective coating
Incident angle
an angle between a beam incident on a surface and the line perpendicular to the surface at the point of incidence.

Related terms: Incidence angle, Angle of incidence, Normal incidence
Infrared leak detector
(IR leak detector)
an IR detector for identifying leaks (and sometimes, concentrations) of selected gases.

Infrared radiationa part of the electromagnetic spectrum with a wavelength longer than visible light and shorter than microwaves. The term “infrared radiation” typically refers to a wavelength range of 0.7 -1000 µm, however practical use of the infrared rays is limited to a range of 0.7 -50 µm.

Related terms: IR radiation, Near infrared, Middle infrared, Far infrared, Near IR, Mid IR, Far IR, Infrared absorbing, IR absorbing layer, IR absorbing coating, IR absorbing film, Infrared emitter, IR emitter, Passive infrared system, Passive IR system, Thermal infrared, Reflective infrared
Infrared detector (IR detector)a sensor that reacts to infrared radiation. Most types of IR detectors give an electrical signal as output.

Related terms: Infrared image detector, Cooled infrared detector, Uncooled infrared detector
Infrared sensor(IR sensor)a type of sensor capable of detecting an object (a hand, arm, or body) based on the infrared radiation emitted by the object.

Related terms: IR sensor, Infrared sensor, IR detector, Infrared detector, IR sensor-detector, Infrared sensor-detector, Infrared detector-emitter, IR detector-emitter
Integrating sphere
an optical device used to either collect flux reflected or transmitted from a sample into a hemisphere or to provide isotropic irradiation of a sample from a complete hemisphere. It consists of a cavity that is approximately spherical in shape with apertures for admitting and detecting flux and usually having additional apertures over which the sample and reference specimens are placed.
Irradiancea radiant flux in any or all directions in a hemispherical solid angle that is incident upon, passing through, or leaving a surface

Related terms: Ideal selective surface, Ideal selective coating


Lambert’s cosine law (Cosine emission law)
a law states that the total radiant power observed from a Lambertian surface is directly proportional to the cosine of the angle θ between the observer’s line of sight and the surface normal.

Related terms: Lambert’s emission law
Lambertian surface a surface that obeys to Lamberts cosine law. Lambertian surface is a perfectly matte surface.
Laser Optics Any kind of optical equipment or component, incorporating materials (substrate or coating) especially designed for working with lasers, are defined as laser optics. Laser optics achieve higher performance in laser systems, by having their parameters calibrated to focus on a specific wavelength or wavelengths, and by having higher then usual laser damage thresholds.
Laser measurement a non-contact measurement of length, width, thickness, straightness, flatness, roughness, diameter, shape, etc based on laser technologies. Hot, soft, sticky, elastic, sterile or moving fast materials can be measured precisely.
Related terms: Laser measurement system, Laser measuring sensor, Laser light meter, Laser power meter, laser energy meter, Laser power and energy meter
Light-Emitting Diode (LED)a semiconductor device that emits a light (usually visible or infrared) when forward-biased.
Liquid crystal display matrix (LCD matrix)LCD elements arranged in a rectangular array
Liquid crystal display panel (LCD panel)a panel that uses a liquid crystal material made of polarized molecules to produce an image. An electric field is induced in the liquid, thereby causing the crystals to align so that light cannot pass through them. There are two types of LCD panels: with active matrix and passive matrix
Related terms: LCD display, LCD screen, Active matrix LCD, Passive matrix LCD, Active LCD screen, Passive LCD screen, Transmissive LCD display, Reflective LCD display
Low reflectivity

related terms: Ames 24E paint, AZKO463 (Sikkens, Cat-A-Lac) paint, Ball IR black paint, Chemglaze (Aeroglaze) Z306 and Z302 paints, Eccosorb 268E paint, Parsons Black paint, black anodize, black hardlub, black hardcoat, Martin Black, InfraBlack, Enhanced Martin Black, Ebonal C, Teflon, ion beam textured, appliques, black chrome, black etched beryllium on beryllium, plasma sprayed boron on beryllium, plasma sprayed beryllium, boron carbide on POCO graphite and Kapton.
opaque materials, IR, UV, low reflectance materials, undesired reflection, incident light suppression, optical noise to signal ratio (Optical S/N ratio), Random Stray Light blocking, Light scattering, low fluorescence.
LWIRa long wave infrared region, a sub-region of the infrared radiation with the wavelengths between 8 and 12 µm.

LWIR camera a FLIR camera working in LWIR range


a middle wave infrared region, a sub-region of the infrared radiation in the wavelengths between 3 and 5 µm.

MWIR camera a FLIR camera working in MWIR range


Night vision an ability to see, whether through biological or technological means, in a dark environment. Most instances, whether biological or technological, use a combination of two approaches: enhanced spectral range, and enhanced intensity range.
Related terms: Night-vision system, Night-vision device, Night-vision appliance, Night-vision optical device, Infrared vision, IR vision, Thermal vision, Thermal night vision optical device
Normal emissivity an emissivity of a body into the direction normal to its surface.
Related terms: Normal emittance


OLED (Organic Light-Emitting Diode)a flat device made by placing a series of organic thin films between two conductors. When electrical current is applied, a bright light is emitted. Another term for OLED is OEL.
Opaque surface (Opaque coating) a surface (coating) having a zero transmittance.
Related terms: Opaque surface layer, Zero transmittance coating, Zero transmittance surface, Zero transmittance surface layer
Optical coating a thin layer of material placed on an optical component such as a lensor mirror, or other substrate which alters the way in which the optic reflects, absorbs, or transmits the light
Related terms: Magenta coating, Fully coated, Multi-coated, Fully multi-coated, Multi-layer coated, Fully multi-layer coated
Optoelectronics(Electro-optics) a study and application of electronic devices that interact with light. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared.
Related terms: Optical system, Baffles, Diaphragms, Lens barrel, Fiber optics, Optical fiber


PDP (plasma display panel) an emissive flat panel display where light is created by phosphors excited by a local plasma discharge.
Photo-detector a sensor that operates in ultraviolet, visible light, or infrared parts of the electromagnetic spectrum.
Related terms: Photoconductive detector, InGaAs photodiode, Germanium photodiode, Lead sulfide photoconductive detector, PbS photoconductive detector, Lead selenide photoconductive detector, PbSe photoconductive detector, Indium arsenide photovoltaic detector, InAs photovoltaic detector, Platinum silicide photovoltaic detector, PtSi photovoltaic detector, Indium antimonide photoconductive detector, InSb photodiode detector, MCT photoconductive detector
Pyroelectric sensor a sensor whose principle is based on pyroelectric detectors absorbing radiation and converting it into heat in a crystal. The changing temperature during heating or cooling of the crystal generates a displacement current between the detector electrodes.


Radiationan energy emitted in the form of electromagnetic waves. In accordance with wavelengths it is customary to divide the electromagnetic spectrum on gamma rays, X-rays, ultraviolet rays, visible light, infrared rays, microwaves and radiowaves.
Related terms: Thermal radiator, Thermopile, Thermocouple, Pyranometer
Reflection a physical phenomenon in which a part of radiant energy falling on a body reflects off the body. Reflection from the surface can be either specular, or diffuse. Flat, smooth surfaces like mirrors and many metal surfaces exhibit specular reflection (angle of reflection of the reflected beam is equal to the angle of the incident beam). Rougher surfaces such as paper are diffuse reflectors (the reflected light is distributed over a wide range of angles). Of course for many materials their reflectivity is a combination of specular and diffuse reflection
Related terms: Low-reflection, Low-reflection coating, Low-reflection surface, Low-reflection layer, Low-reflection surface layer
Reflectance a measure of the ability of a body to reflect the incident radiant energy. Quantitatively, reflectance is defined as the ratio of the reflected radiant energy to incident radiant energy.
Related terms: Low-reflectance, Low- reflectance coating, Low- reflectance surface, Low- reflectance surface layer, Reflectance factor
Reflectivity(1) same as reflectance; (2) ability of a body to reflect incident light.
Related terms: Low-reflectivity, Nonreflective surface


Sensor a device that converts radiation into electrical signals. For example, an optical sensor detects the intensity or brightness of light, or the intensity of red, green and blue color systems. This is usually accomplished by the use of various photoelectric devices.
Related terms: Optical sensing, Pattern-recognition system, Military reconnaissance, High precision imagery, High precision imaging
Selective surface(Selective coating)a surface (coating) having a high absorbance ? in one wavelength range and low emittance ? in another wavelength range. A typical example of spectrally selective surface is a surface required for absorber plate of solar collector. It requires a high absorbance in the range of 0.3 to 3 µm (that is the main solar spectrum range covering part of UV, visible and a part of near IR) and low emittance in the range of 3 to 20 µm (covering near IR and mid IR). Quantitatively, a selectivity of the surface can be expressed as ?/?.
Related terms: Spectrally selective coating, Spectrally selective surface, Selective surface layer, Optically selective coating, Optically selective surface, Optically selective surface layer, Black selective coating, Selective black coating, Selective emissivity
Solar collector a device for extracting energy of the sun directly into a more usable or storable form, for example heat. Sometimes, the term solar absorber is used instead of the term solar collector.
Related terms: High solar absorbance, High solar absorptance, Low infrared emittance, Low infrared emissivity, High solar infrared reflectance
Solar radiation a heat energy emitted from the sun, including ultraviolet, visible and infrared wavelengths. Most (99%) of the sea level solar radiation is in the wavelength range between 0.28 and 3 ?m.
Related terms: Solar spectrum, Solar irradiance, Solar energy, Solar radiant energy
Solar reflectance (see also reflectance) a measure of the ability of a body to reflect the incident sunlight. Quantitatively, solar reflectance is defined as the ratio of reflected solar energy to incident solar energy. Solar reflectance is also called “albedo”
Specular reflection a perfect mirror-like reflection, which obeys two optical laws:
* the angle of incidence is equal to the angle of

* the reflected ray is always in the same plane as
both the incident ray and the normal to the
specular surface.

Examples of specular reflective surface are liquid surfaces, polished metals and glass.
Specular reflectancea measure of specular reflection. Quantitatively, specular reflectance is defined as the ratio of reflected solar energy to incident solar energy at specified incident angle
Spectral emissivity(spectral emittance)a ratio of emittance at a specific wavelength (or narrow range) to that of a blackbody at same temperature.
Stray light an undesirable radiation that reduces image contrast and quality in imaging systems. This undesirable radiation appears in the image as a ”veiling glare”. Stray light is a well-known problem for camera manufacturers. This problem usually arises from a phenomena of parasitic reflection and/or scattering from the lenses and the housing. The camera manufacturers have learned to reduce stray light in their system by using anti-reflection coatings, black paints, and baffles.
Related terms: Stray light rejection, Stray light absorption, stray light reduction, Stray light management, Light trap, Light trapping, Parasite reflection
Stray light surface(coating) a surface (coating) having a high absorbance with respect to stray light.
Related terms: Stray light rejecting coating, Stray light absorbing coating, Stray light rejecting surface, Stray light absorbing surface
SWIR short wave infrared region, a sub-region of the infrared radiation in the wavelengths between 1 and 3 µm.
Related terms: SWIR focal plane array, SWIR FAP
Space-borne infrared instruments
Related terms: Telescope housing and baffles, light shields, cold stops, detectors.


Thermal conductivity(Thermal conductance) a property of a material which characterizes the ability of the material to conduct heat.
Related terms: Low thermal conductivity, High thermal conductivity, Low thermal conductance, High thermal conductance, Thermally conductive, Thermally non- conductive
Thermal mass in the most general sense, is any mass that absorbs and holds heat. In the architectural sense, it is any mass that absorbs and stores heat during sunny periods when the heat is not desirable in a building, and then releases the heat during overcast periods or during the night, when the heat is desirable.
Related terms: Low thermal mass
Thermal radiator a radiation body from which light is emitted by heating a material; generally tungsten, as the filament material in an incandescent lamp
Related terms: Thermal efficiency, Thermally efficient, Thermal emitter
Thermographya method of remote determination of the temperature of an object, based on the measurement of the infrared radiation, emitted by the object. In the case of very hot objects in the nearIR or visible ranges the thermography is termed pyrometry.
Related terms: Thermographic applications, Thermal imaging, Thermal control system (TCS), Passive thermal control system (PCTS)
Thermographic camera (infrared camera, IR camera)a device that forms an image using infrared radiation (thermal imaging), similar to a common camera that forms an image using visible light. Instead of the 450–750 nm range of the visible light camera, infrared cameras operate in wavelengths as long as 14µm.
Related terms: Thermal imaging camera, Thermal imaging infrared camera, infrared imaging, IR imaging
Thin-film deposition any technique for depositing a thin film of material onto a substrate or onto previously deposited layers. Most deposition techniques allow to produce a film with a thickness of few tens of nanometers.
Related terms: Physical vapor deposition, Chemical vapor deposition, Thermal evaporation, Sputtering, Thin black film material
TML (total mass loss) a total mass of material outgassed from a specimen that is maintained at a specified constant temperature and operating pressure for a specified time. TML is calculated from the mass of the specimen as measured before and after the test and is expressed as a percentage of the initial specimen mass.
Related terms: Outgassing in vacuum, Outgassing in vacuum environment
TML and CVCM test a testing technique for determination of volatile content of materials when exposed to a vacuum environment. Two parameters are measured: total mass loss (TML) and collected volatile condensable materials (CVCM). An additional parameter, the amount of water vapor regained (WVR), can also be obtained after completion of exposures and measurements required for TML and CVCM.
Related terms: TML and CVCM from outgassing in a vacuum environment test, Outgassing test, Low outgassing, Low outgassing coating
Total emissivity a ratio of the integrated value of all spectral emittances to that of a blackbody
Transmission a physical phenomenon in which a part of radiant energy falling on a body passes directly the body.
Transmittance a measure of the ability of a body to transmit the incident radiant energy. Quantitatively, transmittance is defined as the ratio of radiant energy passed through the body to incident radiant energy.
Related terms: Low transmittance


Ultraviolet light (UV light)a part of the electromagnetic spectrum with a wavelength longer than X-rays and shorter than visible light. The term “ultraviolet light” typically refers to a wavelength range of 0.1 – 0.4 µm.
Related terms: Ultraviolet radiation ,UV radiation, UV light absorption, Ultraviolet absorbing surface, UV absorbing surface, Ultraviolet absorbing coating, UV absorbing coating, Ultraviolet absorbing layer, UV absorbing layer


Vacuum deposited coating a thin film (coating) produced by vacuum deposition technique, e.g. thermal evaporation, sputtering, etc.
Related terms: Vacuum coating, Vacuum technique, Vacuum technology, Vacuum deposited film, Vacuum deposited thin film
Visible light a part of the electromagnetic spectrum visible by a human eye. The term “visible light” typically refers to a wavelength range of 0.4 – 0.7 µm, thus lying in the electromagnetic spectrum between the infrared waves and the ultraviolet waves.
Related terms: Visible-near infrared, Visible-near infrared region, Visible-near infrared range, Visible-near infrared system, Visible-near infrared reflectance, Visible-near infrared imaging
V-coating a multilayer antireflection coating that substantially reduces the reflectance of a component to near zero for one very specific wavelength. Typically, V-coatings are intended for use at normal incidence, for maximum reflectance of not more than 0.25% at their design wavelength.


Wavelength a distance between adjacent crests or troughs of a monochromatic wave.
Wavenumbera reciprocal of wavelength,usually expressed in cm–1
Wien’s law (Wien’s displacement law) is a law that states that there is an inverse relationship between the wavelength ?max corresponding to the peak of the emission energy of a black body and its absolute temperature T. Particularly, if the wavelength is measured in µm, then ?max = 2900/T
WVR (water vapor regained) a mass of the water vapor regained by the specimen after the optional reconditioning step. WVR is calculated from the differences in the specimen mass determined after the test for TML and CVCM and again after exposure to a 50 % relative humidity atmosphere at 23 degrees C for 24 h. WVR is expressed as a percentage of the initial specimen mass.
Related terms: TML and CVCM test

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