# ASTM E349-06 (Reapproved 2014)

Designation: E349 − 06 (Reapproved 2014)Standard Terminology Relating toSpace Simulation1This standard is issued under the fixed designation E349; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThese definitions pertain to technologies related to space environment simulation. Where possible,existing international and national standard definitions have been used.ELECTROMAGNETIC RADIATION TERMSFUNDAMENTAL CONCEPTSabsorption, n—transformation of radiant energy to a differentform of energy by interaction with matter.complex radiation, n—radiation composed of a number ofmonochromatic radiations.diffusion, n—change of the spatial distribution of a beam ofradiation when it is deviated in many directions by a surfaceor a medium.emission, n— release of radiant energy.infrared radiation, n—radiation for which the wavelengths ofthe monochromatic components are greater than those forvissible radiation, and less than about 1 mm.NOTE 1—The limits of the spectral range of infrared radiation are notwell defined and may vary according to the user. Committee E-2.1.2 of theCIE distinguishes in the spectral range between 780 nm and 1 mm:IR-A 780 to 1400 nmIR-B 1.4to3µmIR-C 3µmto1mmirradiation, n—application of radiation to an object.monochromatic radiation, n—radiation characterized by asingle frequency. By extension, radiation of a very smallrange of frequency or wavelength that can be described bystating a single frequency or wavelength.radiation, n—(1 ) emission or transfer of energy in the form ofelectromagnetic waves or particles.(2) the electromagnetic waves or particles.NOTE 2—In general, nuclear radiations and radio waves are notconsidered in this vocabulary, only optical radiations, that is, electromag-netic radiations (photons) of wavelengths lying between the region oftransition to X-rays (1 nm) and the region of transition to radio waves (1mm).reflection, n—return of radiation by a surface without changeof frequency of the monochromatic components of which theradiation is composed.refraction, n—change in the direction of propagation ofradiation determined by change in the velocity of propaga-tion in passing from one medium to another.spectrum of radiation, n—(1) spatial display of a complexradiation produced by separation of its monochromaticcomponents.(2) composition of a complex radiation.transmission, n—passage of radiation through a mediumwithout change of frequency of the monochromatic compo-nents of which the radiation is composed.ultraviolet radiation, n—radiation for which the wavelengthsof the monochromatic components are smaller than those forvisible radiation and more than about 1 nm.NOTE 3—The limits of the spectral range of ultraviolet radiation are notwell defined and may vary according to the user. Committee E-2.1.2 of theCIE distinguishes in the spectral range between 100 and 400 nm:UV-A 315 to 400 nmUV-B 280 to 315 nmUV-C 100 to 280 nmvisible radiation, n—any radiation capable of causing a visualsensation.NOTE 4—The limits of the spectral range of visible radiation are notwell defined and may vary according to the user. The lower limit isgenerally taken between 380 and 400 nm and the upper limit between 760and 790 nm (1 nanometer, nm = 10−9m).QUANTITIESabsorptance, n—ratio of the absorbed radiant or luminous fluxto the incident flux. Symbol: αe, αv, α.1These definitions are under the jurisdiction ofASTM Committee E21 on SpaceSimulation and Applications of Space Technology and are the direct responsibilityof Subcommittee E21.02 on Terminology, Units and Editorial.Current edition approved April 1, 2014. Published April 2014. Originallyapproved in 1968. Last previous edition approved in 2006 as E349 – 06. DOI:10.1520/E0349-06R14.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1NOTE 5—In general, the value of the absorptance depends upon themode of irradiation, the spectral composition, and the state of polarizationof the incident radiation.absorptivity of an absorbing material, n—internal absorp-tance of a layer of the material such that the path of theradiation is of unit length.diffuse reflection, n—diffusion by reflection in which, on themacroscopic scale, there is no regular reflection.diffuse transmission, n—transmission in which diffusion oc-curs independently, on the macroscopic scale, of the laws ofrefraction.directional emissivity of a thermal radiator, n—ratio of thethermal radiance of the radiator in a given direction to that ofa full radiator at the same temperature. Symbol: ε(θ, φ); ε(θ,φ)=Le,th(θ,φ)/Le(ε =1).emissivity of a thermal radiator, n—ratio of the thermalradiant exitance of the radiator to that of a full radiator at thesame temperature. Symbol: ε, ε = Me,th/Me(ε = 1).NOTE 6—Formerly “pouvoir émissif” (fr.).frequency, n—reciprocal of the period. Symbol; f, ν.NOTE 7—When the independent variable is time, the unit of frequencyis the hertz. Symbol: Hz (1 Hz = 1 s−1). (This unit is also called “cycle persecond,” c/s.)full radiator: blackbody (USA), Planckian radiator,n—thermal radiator that absorbs completely all incidentradiation, whatever the wavelength, the direction ofincidence, or the polarization. This radiator has, for anywavelength, the maximum spectral concentration of radiantexitance at a given temperature.goniophotometer, n—photometer for measuring the direc-tional light distribution characteristics of sources, lightingfittings, media, and surfaces.NOTE 8—A goniophotometer for measuring the spatial distribution ofluminous intensity is also called a distribution photometer.gray body, n—nonselective radiator whose spectral emissivityis less than one.integrating (Ulbrecht) sphere, n—part of an integratingphotometer. A sphere that is coated internally with a whitediffusing paint as nonselective as possible and is providedwith an associated equipment for making a photometricmeasurement at a point of the inner surface of the sphere. Ascreen placed inside the sphere prevents the point underobservation from receiving any radiation directly from thesource.internal absorptance of a homogeneous nondiffusing plate,n—ratio of the radiant or luminous flux absorbed betweenthe entry and exit surfaces of the plate to the flux whichleaves the entry surface. Symbol: ai, ai+ τi=1.NOTE 9—For a given plate, the internal absorptance is a function of thepath length of the radiation in the plate and thus of the angle of incidence.The fundamental concept is spectral internal absorptance. ai(λ).internal transmission density, n—logarithm to the base 10 ofthe reciprocal of the internal transmittance. Symbol: Di,Di= −log10τi.NOTE 10—See Note 12 of internal transmittance.NOTE 11—In German, the symbol E is still in use and the naturallogarithm is also used sometimes instead of the common logarithm; thecorresponding quantity is then called “natürliches Absorptionsmass.”(= In 1/τi).internal transmittance of a homogeneous nondiffusingplate, n—ratio of the radiant or luminous flux reaching theexit surface of the plate to the flux which leaves the entrysurface.NOTE 12—For a given plate, the internal transmittance is a function ofthe path length of the radiation in the plate and thus of the angle ofincidence. The fundamental concept is “spectral internal transmittance”τ(λ).irradiance at a point on a surface, n—quotient of the radiantflux incident on an element of the surface containing thepoint by the area of that element. Symbol: Ee, E; Ee=dΦe/dA; Unit: Watt per square metre, W·m−2.NOTE 13—In ultraviolet radiation therapy and photobiology, thisquantity is called dose rate (International Photobiology Committee, 1954).linear absorption coefficient of an absorbing medium,n—quotient of the internal absorptance of a path elementtraversed by the radiation, by the length d of this element.Symbol: a;−dΦ = aΦdl; Unit: m−1; al =ln10Di.NOTE 14—The linear absorption coefficient is also the part of the linearattenuation coefficient that is due to absorption.NOTE 15—In German practice, a linear absorption coefficient is alsodefined for a homogeneous medium of finite thickness d, as the quotientof the “Absorptions-mass” (logarithm of the reciprocal of the internaltransmittance), by the thickness d of the layer. According to whether thenatural logarithm or the logarithm to the base 10 is used, one maydistinguish the “natürliche Absorptionskoeffizient” (mn) quotient of the“natürliche Absorptionsmass” (see Note 2, internal transmission den-sity) by the thickness d of the layer traversed by the radiation, and the“dekadischeAbsorptionskoeffizient” (m) quotient of the internal transmis-sion density by the thickness d of the layer.NOTE 16—a/ρ, where ρ is the density of the medium, is called “massabsorption coefficient.”linear attenuation (extinction) coefficient of an absorbingand diffusing medium, for a collimated beam of radiation,n—quotient of the relative decrease in spectral concentrationof radiant or luminous flux of a collimated beam of radiationduring traversal with normal incidence of an infinitesimallayer of the medium by the thickness of that layer. Symbol:µ;−dΦ =µΦdl; Unit: m−1.NOTE 17—This concept only applies strictly to slightly diffusing media.NOTE 18—µ/ρ, where ρ is the density of the medium, is called the “massattenuation coefficient.”mixed reflection, n—partly regular and partly diffuse reflec-tion.NOTE 19—The irradiance or illuminance received from a point sourceafter regular (diffuse) reflection varies inversely as the square of thedistance to the source (diffuser).mixed transmission, n—partly regular and partly diffusetransmission.E349 − 06 (2014)2NOTE 20—The irradiance or illuminance received from a point source,after regular (diffuse) transmission, varies inversely as the square of thedistance to the source (diffuser).nonselective radiator, n—thermal radiator whose spectralemissivity is independent of wavelength over the rangeconsidered.opaque body, n—body that transmits practically no light.period, n—size of the minimum interval of the independentvariable after which the same characteristics of a periodicphenomenon recur.NOTE 21—In radiation, the independent variable is the time and thecorresponding quantity is the periodic time: Symbol: T; Unit: second (s).photometer, n—instrument used for measuring photometricquantities.photometry, n—measurement of quantities referring toradiation, evaluated according to the visual effect which itproduces, as based on certain conventions.radiance (in a given direction, at a point on the surface of asource or receptor or at a point in the path of a beam), ,n—quotient of the radiant flux leaving, arriving at, or passingthrough an element of surface at this point and propagated indirections defined by an elementary cone containing thegiven direction by the product of the solid angle of the coneand the area of the orthogonal projection of the element ofsurface on a plane perpendicular to the given direction.Symbol: Le, L; Le=d2Φ (dω dA cos Θ); Unit: Watt persteradian and per square metre, W·sr−1m−2.NOTE 22—Three special cases may be noted:Case 1—At a point on the surface of a source, in a given direction,radiance is also the quotient of the radiant intensity in the given directionof an element of the surface at this point, by the area of the orthogonalprojection of this element on a plane perpendicular to this direction(radiant intensity per unit projected area). Le=dIe/(dA cos Θ).Case 2—At a point on the surface of a receptor, in a given direction,radiance is also the quotient of the irradiance that is received at this pointon a surface perpendicular to the given direction by the solid angle of theelementary cone containing this direction and surrounding the beam whichproduces this irradiance (perpendicular irradiance per unit solid angle).Le=dEe/dω.Case 3—On the path and in the direction of an element of a beam, ina nondiffusing, nonabsorbing medium, the radiance is also the quotient ofthe radiant flux dΦewhich transports the beam, by the geometric extentdG of the beam. The geometric extent, which may be defined by twosections of the beam of areas dA and dA of separation l, and having anglesΘ and Θ between their normals and the direction of the beam is dG =dAcos Θ dω where the numerical value in steradians of dω is dA cos Θ l−2.L0=dΦ0/dG =d2Φe/(dω dA cos Θ). In the absence of diffusion, it can bedemonstrated in geometrical optics that the optical extent, product of thegeometric extent of an element of a beam and the square of the refractiveindex of the medium of propagation, is an invariant along the length of thebeam whatever the deviations that it undergoes by reflection or refraction(dG·n2= constant). In consequence, the basic radiance, quotient of theradiance by the square of the refractive index, is invariant along the lengthof an element of a beam if losses by absorption or by reflection are takenas zero (Le·n−2= constant).radiance factor at a point on the surface of a nonself-radiatingbody, in a given direction under specified conditions ofirradiation,, n—ratio of the radiance of the body to that of aperfect reflecting or transmitting diffuser, identically irradi-ated. Symbol: β.radiant efficiency of a source of radiation, n—ratio of theradiant flux emitted to the power consumed. Symbol: ηe, η.NOTE 23—The radiant efficiency of a source in a limited region of thespectrum may also be considered, that is, the ratio of the radiant fluxemitted in this spectral region to the power consumed.radiant energy, n—energy emitted, transferred, or received asradiation. Symbol: Qe, Q; Unit: joule J (1 J = W·s).NOTE 24—In ultraviolet radiation therapy and photobiology, thisquantity is called “integral dose” (International Photobiology Committee,1954).radiant exposure at a point on a surface, n—surface densityof the energy received. Symbol: He, H; He=dQe/dA = ∫ Eedt; Unit: joule per square metre, J·m−2.NOTE 25—Formerly “irradiation.”NOTE 26—Equivalent definition: Product of an irradiance and itsduration.NOTE 27—In ultraviolet radiation therapy and photobiology, thisquantity is called dose (International Photobiology Committee, 1954).radiant exitance at a point on a surface, n—quotient of theradiant flux leaving an element of the surface containing thepoint, by the area of that element. Symbol: Me, M; Me=dΦe/dA = ∫2Lecos θdω. Unit: Watt per square metre, W·m−2.NOTE 28—The name radiant emittance previously given to this quantityis abandoned because it has given rise to confusion. Thus, the term“emittance” has been used to designate either the flux per unit area leavinga surface (whatever the origin of the flux), the flux per unit area emittedby a surface (flux originating in the surface), or, principally, in certaincircles in the United States of America, a qua