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SOLAR RADIATION GLOSSARY:

Air Mass

Albedo

The ratio of the amount of radiation reflected by a surface to the amount incident upon it.

Azimuth Angle

An angle of a plane to the horizon measured clockwise to the object

Collimated Beam

A light beam in which all rays are parallel.

Emissive Power or Radiant Self Exitance, W/m²

The rate at which radiant energy leaves a surface per unit area, by emission only.

Intensity

Luminous or radiant flux radiated by a source.

Irradiance, Infrared

Radiation per unit area for which the wavelengths of the monochromatic components are greater than those for visible radiation, and less than about 1 mm. Note: The limits of the spectral range of infrared radiation may vary according to the user. Committee E-2.1.2 of the CIE distinguishes in the spectral range between 780 nm and 1 mm: IR-A 780 to 1400 nm, IR-B 1.4 to 3 µm, IR-C 3 µm to 1 mm.

Irradiance, Ultraviolet

Radiation per unit area for which the wavelengths of the monochromatic components are shorter than those for visible radiation. Note: The limits of the spectral range of ultraviolet radiation may vary according to the user. Committee E-2.1.2 of the CIE distinguishes in the spectral range between 100 and 400 nm: UVA 315 to 400 nm, UVB 280 to 315 nm, UVC 100 to 280 nm.

Irradiance,Visible

The rate at which radiant energy is incident on a surface per unit area (W/m²).

Irradiance

A measure of the visibility of brightness-producing capacity of radiant energy consisting in the ratio of photometric quantity to corresponding radiometric quantity in standard units (lumens per watt).

Luminous Flux

A measure of the visibility of brightness-producing capacity of radiant energy consisting in the ratio of photometric quantity to corresponding radiometric quantity in standard units (lumens per watt).

Light

The part of solar radiation that the human eye can detect (photopic vision, V~)

Pyranometer

An instrument for measuring total hemispherical solar beam + diffuse radiation, usually on a horizontal surface. If shaded from the beam radiation by a shade ring or disc, a pyranometer measures diffuse radiation.

Pyrheliometer

An instrument using a collimated detector for measuring solar radiation from the sun and from a small portion of the sky around the sun (i.e., beam radiation) at normal incidence.

Radiant Energy

Energy traveling through space in the form of photons or electromagnetic waves of various lengths.

Radiation, Actinic

The spectral region(s) of a light source responsible for the photodegradation of a particular material.

Radiation, Direct

The solar radiation received from the sun without having been scattered by the atmosphere. (Direct radiation is often referred to as beam radiation).

Radiation, Diffuse

The solar radiation received from the sun after its direction has been changed by scattering in the atmosphere. (Diffuse radiation is referred to in some meteorological literature as sky radiation or solar sky radiation; the definition used here will distinguish the diffuse solar radiation from radiation emitted by the atmosphere).

Radiation, Long Wave

Radiation originating from sources at temperatures near ordinary ambient temperatures and, thus, substantially all at wavelengths greater than 3µm. Long-wave radiation is emitted by the atmosphere or by any other body at ordinary temperatures.

Radiation, Solar or Short Wave

Radiation originating from the sun, in the wavelength range of Short Wave 0.3 to 3.0µm. In the terminology used throughout this book, solar radiation includes both direct and diffuse components unless otherwise specified.

Radiation, Total Solar

The sum of the direct and the diffuse radiation on a surface. Total solar radiation is sometimes used to indicate quantities integrated over all wavelengths of the solar spectrum. (The most common measurement of solar radiation is total radiation on a horizontal surface, often referred to as global radiation).

Radiometer

A general class of instruments designed to detect and measure radiant energy.

Radiosity or Radiant Exitance, W/m²

The rate at which radiant energy leaves a surface, per unit area, by combined emission, reflection, and transmission.

Solar Radiant Exposure

The incident energy per unit area on a surface, found by integration of irradiance over a specified time period (J/m²).

Spectral Power Distribution

The variation of energy due to the source over the wavelength span of the emitted radiation.

Spectrum

Spatial arrangement of electromagnetic energy in order of wavelength

Wavelength

The distance, measured along the line of propagation, between two points that are in phase on adjacent waves. Wavelength determines the color of light. Wavelengths of visible light range from about 400 to about 800 nm.

Zenith Angle

~ z The angle subtended by a vertical line to the zenith (i.e., the point directly overhead) and the line of sight to the sun.

MATERIAL PROPERTIES (APPEARANCE ATTRIBUTES) GLOSSARY:

Absorption

Absorption, Selective

The process of absorption which varies with wavelength.

Appearance

The aspect of visual experience by which differences are recognized. An example is the visual evaluation of exposed materials to identical unexposed materials. This is a criteria of visual inspection reports.

Artificial Illuminants

A synthetic light source of spectral distribution as close as possible to that of the natural illuminant (usually daylight) to be duplicated.

Attribute

Distinguishing characteristic of a sensation, perception or mode of appearance.

Bleaching

A phenomenon usually associated with the weathering of paint coatings in which some light-colored coatings become whiter in their appearance.

Blemish

An irregularity visible at the surface of a specimen and not attributed to the natural weathering process.

Bloom

The scattering of light in directions near the specular direction by a deposit or excretion on a specimen. Bloom can be removed by rubbing or polishing.

Brightness

(1) In optics and appearance measurements -- the attribute of visual sensation by which an observer is aware of differences in luminance; (2) in pigments, dyes and colored products -- the attribute of color that corresponds to its perceived difference from the color of dirt; (3) in metals -- freedom of metallic surfaces from reflection haze and texture; (4) in lighting -- the luminous intensity of any surface in a given direction per unit of projected area of the surface as viewed from that direction; (5) in dyeing -- the color quality, a decrease in which corresponds to the effect of the addition of a small quantity of neutral gray dye to the dyestuff, whereby a match cannot be made by adjusting the strength.

Chroma (Munsell)

Departure of color from gray having the same Munsell value, expressed on a scale extending from zero by steps of approximately equal visual importance, to a maximum of about 20. Corresponds to saturation.

Chromatic

Perceived as having a hue; not white, gray, or black.

Chromatic Attributes

Those attributes associated with the spectral distribution of light, specifically hue and saturation.

Chromaticity

That part of a color specification that does not involve luminance. Chromaticity is two dimensional and is given by pairs of numbers, such as dominant wavelength and purity.

CIE, Commission Internationale de l’Eclairage

The main international organization concerned with problems of color and color measurement.

CIE Chromaticity Coordinates

(Trichromatic coefficients or trilinear coordinates) The ratios of each of the tristimulus values of a color to the sum of the tristimulus values.

CIE Standard Sources

Standard sources for which the CIE in 1931 specified the spectral power distribution as follows:

• Illuminant A:
  a tungsten filament lamp operated at a color temperature of 2854K; it approximates a blackbody operating at that temperature.
  
  
• Illuminate B:
  an approximation of noon sunlight having a correlated color temperature of approximately 4870K. It is obtained by a combination of Illuminant A and a special filter.
  
  
• Illuminate C:
  an approximation of overcast daylight having a correlated color temperature of approximately 6770K. It is obtained by a combination of Source A and a special filter.
  

In 1965, CIE recommended new illuminants to supplement Illuminants A, B, and C, the most important of which was D6500, with a correlated color temperature of 6500K. D65 is especially used in the evaluation of fluorescing or brightened materials where the spectral energy distributions of the light source in the 300-400 nm ultraviolet range contribute to color appearance.

CIE Tristimulus Values

The amounts of the three reference or matching stimuli required to give a match with the color stimulus considered, in a given trichromatic system. The symbols recommended for the tristimulus values are X, Y, Z in the CIE (1931) Standard Colorimetric System and X^10, Y¹⁰, Z¹⁰ in the CIE (1964) Supplementary Colorimetric System.

Clarity

The characteristic of a transparent material whereby distinct images may be observed through it.

Color

The visual sensation produced by light of different wavelengths throughout the visible region of the spectrum. By such perception, an observer may distinguish between objects of the same size, shape, and structure.

Color Attribute

A three-dimensional characteristic of the appearance of an object, light source or aperture. One dimension usually defines the lightness, and the other two together define the chromaticity.

Color Difference

The magnitude and character of the difference between two object colors under specified conditions.

Colorimetry

The science of the quantitative measurement of color.

Color Matching

Procedure of adjusting a color mixture until all visually apparent differences from a target color are eliminated.

Color Measurement Scale

A system of specifying numerically the perceived attributes of color.

Color Temperature

The temperature at which the walls of a uniformly heated furnace must be maintained so that light from a small hole in it shall yield the chromacity of the source whose color temperature is to be specified.

Directionality of Surface

The extent to which the appearance of a surface, particularly its glossiness, changes with rotation of the surface in its own plane.

Distinctness-of-Image

The sharpness with which outlines are reflected by the surface gloss of an object.

Dominant Wavelength

The wavelength of spectrally pure energy that, if mixed with white light, would match a color.

Fading

A color change in a material that involves a weakening or lightening with time, usually as a result of exposure to light, weather, etc.

Fluorescence

The process by which electromagnetic radiation of one spectral region is absorbed and reradiated at other, usually longer, wavelengths.

Gloss

(1) Subjective term used to describe the relative amount and nature of mirror-like (specular) reflection or (2) numerical value for the amount of specular reflection relative to that of a standard surface under the same geometric conditions.

Gloss Measurement Scales

Systems of specifying numerically the perceived gloss of an object.

Gray Scale for Color Difference

A system for evaluating visually the color difference between two specimens by comparison with differences between two grays.

Haze

See “transmission haze” and “reflection haze.”

Hue

The attribute of color perception by means of which an object is judged to be red, yellow, green, blue, purple, etc.

Hunter L,a,b Scales

A uniform color scale devised by Hunter in 1958 for use on a color difference meter, based on Hering’s opponent color theory of vision.

Hunter L’,a’,b’ Scales (Rh Scale)

A uniform color scale proposed by Hunter for use with dark colors and with transparent and metallic objects, which uses Y instead of Y1/2 as the lightness factor.

Hunter Rd,a,b Scales

A uniform opponent-color scale devised by Hunter in 1948, used for the analog scales of the color difference meter; the forerunner of the Hunter L,a,b scale.

ICI

International Commission on Illumination.

Illuminant

Incident luminous energy specified by its spectral distribution.

Lightfastness

The resistance to color change when exposed to a light source.

Lightness

Perception by which white objects are distinguished from gray, and light from dark-colored objects.

Luster (contrast gloss)

A highlight or glossiness perception in which shifty bright areas are seen on the surface of an object. Luster increases with increased ratio between light reflected in the specular direction and that reflected in diffuse directions adjacent to the specular direction.

Opacity

The degree to which a sheet or film obscures a pattern beneath it.

Reflection

Process by which incident light leaves a surface or medium from the side on which it is incident.

Reflection, Diffuse

Process by which incident light is redirected over a range of angles from the surface on which it is incident.

Reflection, Specular

Process by which incident light is redirected at the specular angle, as from a mirror, without diffusion.

Reflection Haze

The scattering of reflected light in directions near that of specular reflection by a specimen having a glossy surface. Surface haze cannot be removed by rubbing or polishing.

Saturation

The attribute of color perception that expresses the degree of departure from the gray of the same lightness.

Sheen

Specular gloss at a large angle of incidence for an otherwise matte specimen; the usual angle of measurement is 85°.

Translucency

The property of a material by which a major portion of the transmitted light undergoes scattering.

Transmission

Process by which incident light is transmitted through an object.

Transmission, Diffuse

Process by which incident light, while being transmitted through an object, is redirected, or scattered over a range of angles.

Transmission Haze

The scattering of light within or at the surface of a nearly clear specimen; responsible for cloudy appearance of specimen.

Transmission, Specular

Process by which incident light is transmitted through an object in a rectilinear, straight-through manner, without diffusion.

Transparency

The property of a material by which a major portion of the transmitted light undergoes scattering.

Turbidity

Loss of transparency due to diffusion caused by presence of particulate matter.

Value

The quality which tells us whether a color is light or dark.

Weighted Ordinate Method

A method of arriving at XYZ tristimulus values by multiplication of integrating XYZ values at equal wavelength intervals, of values of spectral reflectance (transmittance) by weighing factors that are products of spectral energy values and spectral tristimulus values, followed by addition of these products.

Whiteness

Perception of high lightness, high diffusion, and absence of hue.

Yellowness

The attribute by which an object color is judged to depart from a preferred white toward yellow.

MATERIAL PROPERTIES (PHYSICAL ATTRIBUTES) GLOSSARY:

Adhesion

Blister

An enclosed elevated area (as in paint) resembling a blister on human skin.

Chalking

The formation on a pigmented coating of a friable powder evolved from the film itself, or just beneath the surface.

Checking

Fractures at the surface of coatings which do not expose the substrate.

Cracking

Fractures that expose previous coatings or substrates.

Crazing

A system of cracking or checking visible at the surface of materials.

Defect

Any irregularity occurring in or on a material as a result of degradation.

Delamination

A separation of distinct layers of materials in a laminate.

Elongation

The increase in gauge length of a tension test specimen, usually expressed as percentage of the original gauge length.

Flaking

Detachment of paint film from previous coating or substrate.

Hardness

The resistance of a material to deformation, particularly permanent deformation, indentation, or scratching.

Pinholes

Small, pore-like flaws in a material extending entirely through an applied film and which have the appearance of pin pricks when viewed by reflected light.

Scaling

See "flaking".

Shear Strength

The maximum shear stress that a material is capable of sustaining. Shear strength is calculated from the maximum load during a shear or torsion test and is based on the original dimensions of the cross section of the specimen.

Spectrophotometry

Use of a spectrophotometer, an instrument for measuring the transmittance and reflectance of surfaces and media as a function of wavelength.

Surface Uniformity

Freedom of a surface from texture or markings.

Tensile Strength

The maximum tensile stress that a material is capable of sustaining. Tensile strength is calculated from the maximum load during a tension test carried to rupture and the original cross-sectional area of the specimen.

Texture

Structural quality of a surface determined by the interrelation of its elements.

Yield Strength

The stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain. The deviation is expressed in terms of strain.

WEATHERING GLOSSARY:

Accelerated Outdoor Weathering

Ambient Air Temperature

The existing temperature of the air or of an object in thermal equilibrium with the surrounding atmosphere.

AATCC Blue Wool

Standard dyed-wool samples of seven grades, each step in the series representing a doubling of lightfastness. Used as a calibration and verification tool in AATCC Test Methods.

Black Box

A black-painted aluminum box with an open top where the flat test specimens to be exposed constitute the top surface of the box. The box is equipped with mounting strips to hold the test specimens firmly in place. The top surface of the box must be completely filled at all times; any blank spaces on the top surface must be occupied by black “dummy” panels to maintain correct operating conditions.

Black Box Under Glass

A glass-covered enclosure or cabinet of any convenient size. It shall be constructed of corrosion-resistant metal and be enclosed to prevent ambient air from circulating over the samples. Exterior non-glass surfaces shall be painted black. The interior shall remain unpainted.

Black Panel Thermometer

A temperature measuring device consisting of a metal panel, having a black coating that absorbs all wavelengths uniformly, with a thermally sensitive element firmly attached to the center of the exposed surface. The black panel thermometer is used to control a laboratory weathering device and to provide an estimate of the maximum temperature of samples exposed to a radiant energy source.

Black Standard Thermometer

A temperature measuring device consisting of an insulated black plastic which absorbs all wavelengths of radiation uniformly, with a thermally sensitive element firmly attached on the center of the unexposed surface. The black standard thermometer is used to control specimen temperature in air-cooled xenon arc devices.

Climatological types

Major regions of significantly different recurring weather patterns. In weathering, several distinct climatological types are used to evaluate the atmospheric durability of materials within any single climatological variation, at a specific geographic location.

Control

The term “control” has three current widespread uses:

(1) A material of similar composition and construction to the test material used for comparison, exposed at the same time.

(2) A portion of the material to be tested that is stored under conditions in which it is stable, and is used for comparison between exposed and original state.

(3) A portion of the exposed specimen that is protected from light exposure by masking.

Corrosion

Chemical or electrochemical oxidation of a surface of metal which can result in loss of material or accumulation of deposits.

Dewpoint

The temperature at which moisture in the air begins to condense. The temperature below which condensation of water vapor begins to take place when the atmosphere is cooled.

Durability

In weathering, a measure of the retention of original condition and function of a material after exposure to a specified set of conditions.

Enclosed Carbon Arc

A light source in which an arc is produced across a pair of carbon rods by a high-energy electrical source, such that a high-intensity light is emitted. The carbons are enclosed in an inverted glass dome, which acts to prolong the life of the carbons, and to modify the spectral power distribution received by the specimens.

Exposure

The act of subjecting a test specimen to test conditions.

Exposure Angle

The tilt from horizontal of the test specimen or any other exposed material, or both.

Exposure, Backed

A technique of weathering in which test specimens being exposed are mounted onto a solid backing material, of sufficient strength to hold the specimen. When the specimen and the backing are in direct contact, the backing material must be of a type that will not contaminate the specimen. When two materials are intimately joined to form one composite, the materials below the top surface are not considered as a backing.

Exposure, Open-Backed

A technique of weathering in which the test specimens are exposed such that the portion of the specimen being evaluated is open to the effects of the weather on all sides.

Fluorescent Ultraviolet Lamp

A lamp in which the irradiance from a low-pressure mercury arc is transformed to a higher-wavelength UV by a phosphor. The spectral power distribution of a fluorescent lamp is determined by the emission spectrum of the phosphor and the UV transmittance of the glass tube.

Fresnel-Reflector System

Flat mirrors arranged in an array such that they reflect onto a target, the illuminated area of which simulates the size and shape of the flat mirror. Such an array simulates the ray-tracing of a parabolic trough of the same aperture angle.

ISO Blue Wool Reference Standard Materials

Standard dyed wool samples, each step in the series representing a doubling of lightfastness. Used to classify the colorfastness of textile materials.

Laminate

A composite material made by adhering two or more layers of the same or different materials.

Light

Electromagnetic radiation in a spectral range visible to the human eye (approximately 400-800 nm).

Masked Area

A portion of the exposed specimen that is protected from light exposure by covering with the exposure rack or other means.

Metal Halide Lamps

Lamps that emit radiation generated by a large number of different chemical components in the arc plasma. The most important components are the Rare Earths (i.e. Dysprosium, Thulium and Holmium) which form halides with the existing halogens. Metal Halide Lamps offer a close match to sunlight. They are an efficient light source with low infrared heating effects.

Nanometer

Unit of length equal to 10^-9 m.

Open Flame Sunshine Carbon Arc

A light source in which an arc is produced across a pair of copper coated carbon rods filled with rare earth elements intended to produce a specific spectral power distribution. The carbons are open to the atmosphere and may be surrounded by a glass lantern arrangement, which acts to modify the spectral power distribution received by the specimens.

Photodegradation

Photochemically induced changes in the condition of the material.

Photodetectors

Devices for converting radiant or luminous flux into an electric current proportional to it.

Primary Standard

A standard whose calibration is determined by the measurement of parameters usually different from the parameter for which it will be used as a standard.

Reference Material

A material with known performance.

Reference Specimen

A portion of the reference material that is to be exposed.

Relative Humidity

The ratio of the actual pressure of existing water vapor to the maximum possible (saturation) pressure of water vapor in the atmosphere at the same temperature, expressed as a percentage.

Sample

A group of units or portion of material taken from a larger collection of units or quantity of material that serves to provide information that can be used as a basis for action on the larger quantity.

Secondary Standards

All standards other than primary standards.

Solarization

Change in transmittance, reflectance, or absorptance property of a material, such as glass, as a result of exposure to sunlight or other light sources.

Standard Reference Material (SRM)

A weathering reference material having well documented weathering degradation properties that have been certified by a recognized standards agency or group and that are identical when exposed to identical test conditions.

Temperature, Dry-Bulb

The temperature of the ambient air; for example, the temperature that is measured by the dry-bulb thermometer of a psychrometer.

Temperature,Wet Bulb

The equilibrium temperature of a liquid vaporizing into a gas.

Test Specimen

A specific portion of the samples upon which the testing is to be performed.

Tilt Angle

The angle between the horizontal and the plane of the test fixture, glass frame, or sensory instrumentation.

Time-Of-Wetness

The total amount of time that a surface is wet. This is typically reported in hours.

Visual Evaluation

The evaluation by an experienced observer of the visual interpretation of the properties of object or material evaluated.

Weathering Behind Glass

A technique of weathering in which the test specimens are exposed in a glass-covered frame constructed of wood, metal, or other satisfactory material that protects the specimen from the effects of rain and weather. The frame shall be open at the back or sides to allow ambient air to circulate over the specimens.

Weathering Reference Material (WRM)

A reference material whose weathering degradation properties are well-documented and repeatable when exposed to identical test conditions. A WRM differs from an SRM in that its weathering history has not been certified by a recognized agency.

White Panel Temperature

White Panel Temperature is the temperature measured on a metal panel with a white low-heat conducting coating and a thermal sensitive element firmly attached to the center of the exposed surface.

White Standard Thermometer

The White Standard Thermometer measures the White Standard Temperature at the sample plane. The White Standard Temperature provides information on the surface temperature of white, low-heat conducting samples during exposure.

Weathering, Direct

A technique of weathering in which the test specimens are exposed to all prevailing elements of the atmosphere.

Weathering, Natural

Outdoor exposure of materials to unconcentrated sunlight, the purpose of which is to assess the effects of environmental factors on various functional and decorative parameters of interest.

Xenon Arc

A light source produced by a high-intensity electrical current through a tube containing low pressure xenon gas. The spectral energy distribution of this light source is generated by the electrical current arcing through the xenon gas plasma between the electrodes, and is modified by filters.