IEC 62862-3-5:2026

• Abstract:

  IEC 62862-3-5:2026 specifies laboratory methods to measure reflectance of all types of reflectors for use in concentrating solar thermal (CST) plants.

• Status: Published
• Publication Date: 28-Sep-2026
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TC 117 - Solar thermal electric plants
• Drafting Committee: PT 62862-3-5 - TC 117/PT 62862-3-5
• Current Stage: PPUB - Publication issued
• Start Date: 29-Sep-2026
• Completion Date: 02-Oct-2026

IEC 62862-3-5:2026 is an International Standard published by IEC for laboratory measurement of reflectance on solar reflectors used in concentrating solar thermal (CST) plants. It specifies how to prepare samples, measure spectral near-normal sun-conic near-specular and hemispherical reflectance, calculate solar-weighted and UV-weighted values, estimate uncertainty, and report the results.

What does IEC 62862-3-5:2026 specify?

IEC 62862-3-5:2026 specifies laboratory methods to measure reflectance of all types of reflectors for use in concentrating solar thermal (CST) plants. The document is organized into clauses for scope, references, terms and definitions, sample preparation, measurement methods, weighting calculations, uncertainty, and reporting, with two informative annexes that offer alternative methods for special cases.

Annex	What it covers
Annex A	Simplified method for reflectors with high specularity
Annex B	Indirect method for deriving near-specular reflectance

Clause 3 establishes the reflectance nomenclature used throughout the document, while Clauses 4 to 8 cover the laboratory workflow from sampling to the final report. In practice, that structure helps a test lab move from receiving a reflector sample to issuing a traceable measurement report.

What are the key requirements of IEC 62862-3-5:2026?

Sample selection and preparation matter because the result must represent the installed reflector

Clause 4.1 requires samples to fit the instrument and, unless the instrument can handle curvature, to lie flat on the sample port. For commercial products, samples should come from the production line and match the final reflector in composition, process, and surface finish. That matters because prototype coupons can give a better-looking result than real production material.

Clause 4.1 also asks for at least three replicate samples and at least three measurement spots per sample, with averages and standard deviations reported. When the surface is heterogeneous or anisotropic, the document recommends more spots and, if needed, measurements on the same spot while rotating the sample. In practice, this is how the lab shows whether the reflectance is uniform enough for field use.

Clause 4.2 requires cleaning before measurement, using dry compressed air and, if needed, water with mild detergent or acetone applied carefully on glass surfaces. The clause excludes measurements intended to determine soiling, where preparation is not needed. This distinction matters because cleaning would remove the very contamination being studied.

Reference coupons and instrument stability are central to repeatable results

Clause 4.3 requires a high-specularity reference coupon with calibration traceable to a certified calibration institute, valid for the wavelength range and incidence angles used. It also recommends keeping at least two identical coupons, with one master reference and one working reference, and comparing them regularly. For a lab, this is the control that keeps different measurement runs comparable over time.

Clause 4.4 requires instruments to avoid stray light, sample damage, and health or environmental hazards, and to have stable sources and low Type B uncertainty. The measurement setup must not be modified between calibration and sample measurement if the instrument has movable parts. That reduces hidden drift in the optics and protects the validity of the calibration.

The standard method measures two reflectance types, then derives the practical weighting values

Clause 5.1 states that the relevant parameter for CST performance is the solar-weighted near-normal sun-conic near-specular reflectance, but commercial instruments usually cannot measure it directly. The standard method therefore combines spectral near-normal sun-conic near-specular measurements with spectral near-normal hemispherical measurements, then calculates solar-weighted or UV-weighted values in Clause 6. For readers, this means the laboratory report is built from measurable quantities plus a calculated performance value.

Clause 5.2 requires spectral near-normal sun-conic near-specular reflectance at a minimum in three wavelengths and three acceptance angles, with values reported separately. The measurements are taken at near-normal incidence, and the divergence of the beam should not exceed the mean solar disc angle. For CST users, this links the reflector’s optical behavior to how well it can redirect sunlight toward the receiver.

Clause 5.3 requires spectral near-normal hemispherical reflectance over the relevant solar spectrum, typically with a commercial spectrophotometer and integrating sphere. The document recommends a sphere diameter of at least 150 mm and a port fraction between 2 % and 4 % of the sphere surface. This is the practical route to capture the total reflected light, not just the near-specular portion.

Weighting calculations use the IEC solar spectrum and defined wavelength ranges

Clause 6 uses the direct-irradiance solar spectrum from IEC 60904-3 with Air Mass AM 1,5. Solar-weighted reflectance is calculated over the range selected by the standard, and UV-weighted reflectance uses the UV ranges defined in the document. The wavelength step is recommended as 5 nm and shall not exceed 10 nm, which affects the resolution and time of the measurement.

For engineers comparing reflector materials, the weighting calculation is what turns spectral data into one practical number. It lets different products be compared on the same solar or UV basis instead of at a single wavelength.

Uncertainty and reporting are part of the required result

Clause 7 requires uncertainty to be calculated according to ISO/IEC Guide 98-3:2008, including Type A results, Type B contributions, and a coverage factor. That makes the reported reflectance value meaningful enough for technical comparisons and supplier discussions.

Clause 8 requires the report to identify the laboratory, client, samples, measurement conditions, instrument, reference coupon, wavelength range, angles, uncertainty, and conclusions. It also requires a statement on whether agreed acceptance criteria were met. In practice, this gives buyers and quality managers the evidence they need to review a test result without re-running the experiment.

Annexes A and B give alternative routes for special materials

Annex A gives a simplified method for highly specular reflectors when diffuse loss beyond the stated acceptance angle is low enough. Annex B gives an indirect method that combines hemispherical reflectance with one monochromatic near-specular measurement to calculate equivalent roughness and then derive spectral near-specular reflectance. Annex B explicitly says the method cannot be applied to soiled reflectors.

What terms does IEC 62862-3-5:2026 define?

• Direct solar radiation - Solar radiation arriving from a small solid angle centered on the sun’s disk.
• Reflector - An optical device made of several materials arranged to provide suitable reflectance properties; the document notes that “mirror” is commonly used as a synonym.
• Angle of incidence - The angle between the incoming beam and the surface normal at the point of measurement.
• Angle of acceptance - The half-apex angle of the cone of reflected rays that the detector or receiver captures.
• Near-normal reflectance - Reflectance measured at a small incidence angle where the value is close to that at normal incidence.
• Solar reflectance - Spectral reflectance weighted over the solar spectrum.
• UV reflectance - Spectral reflectance weighted over the ultraviolet part of the solar spectrum.
• Specularity - The ratio between near-specular reflectance and hemispherical reflectance.

Who uses IEC 62862-3-5:2026?

IEC 62862-3-5:2026 is used by test laboratories measuring reflector samples for CST plants, and by manufacturers of glass, coated, or polymer-based solar reflectors who need to characterize product performance. It is also relevant to quality managers checking production-line samples against accepted product definitions, and to R&D teams studying surface finish, curvature, protective layers, or soiling effects.

Design engineers and buyers can use it to compare reflector materials on the same laboratory basis, especially when specularity and broad-spectrum behavior both matter. The reporting structure also supports clients who need a formal test record for procurement, validation, or technical review.

Which standards are used with IEC 62862-3-5:2026?

• IEC 60904-3 - Provides the reference spectral irradiance data used for solar-weighting and UV-weighting calculations.
• IEC TS 62862-1-1 - Provides terminology for solar thermal electric plants and supports the document’s definitions.
• ISO/IEC Guide 98-3:2008 - Provides the framework for expressing measurement uncertainty.
• ISO 4628-2:2016 - Supports the description of blistering in back protective layers when reporting defects.
• ISO 9488:2022 - Provides solar-energy vocabulary used in the definitions.

What does the IEC 62862-3-5:2026 document contain?

The document includes Figure 1 for the geometry of incidence, reflection, divergence, and acceptance, which is important for understanding what the measurement angles mean. Table 1 organizes the reflectance nomenclature, and Tables 2 and 3 define the UV classes and wavelength ranges used in weighting calculations.

Clause 6 contains Formula (1) for converting spectral reflectance into solar-weighted or UV-weighted reflectance. Annex A sets out the practical check for high-specularity reflectors, and Annex B gives the step-by-step indirect method with formulas for equivalent roughness and derived near-specular reflectance. The bibliography points readers to related literature on uncertainty, integrating sphere practice, and indirect reflector methods.

IEC 62862-3-5 ®
Edition 1.0 2026-09
INTERNATIONAL
STANDARD
Solar thermal electric plants -
Part 3-5: Laboratory reflectance measurement of solar reflectors
ICS 27.160  ISBN 978-2-8327-1472-0

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CONTENTS
FOREWORD . 2
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
3.1 Solar definitions . 4
3.2 Collector components . 4
3.3 Angle definitions . 5
3.4 Optical properties . 5
3.5 Figures and tables . 9
4 Preparation of measurement . 10
4.1 Sampling . 10
4.2 Sample preparation . 11
4.3 Reference coupons . 11
4.4 Instrumentation . 11
5 Measurement method . 12
5.1 General . 12
5.2 Spectral near-normal sun-conic near-specular reflectance . 12
5.3 Spectral near-normal hemispherical reflectance . 13
6 Weighting calculation. 13
6.1 General . 13
6.2 Solar-weighted reflectance . 13
6.3 UV-weighted reflectance . 13
6.4 Calculation equation . 14
7 Uncertainty of the measurement . 14
8 Reporting . 15
8.1 General . 15
8.2 General information . 15
8.3 Methodology . 15
8.4 Results . 16
8.4.1 Uncertainty . 16
8.4.2 Standard method . 16
8.4.3 Simplified method . 16
8.4.4 Indirect method . 17
8.5 Conclusions . 17
Annex A (informative) Simplified method for reflectors with high specularity . 18
Annex B (informative) Indirect method . 19
Bibliography . 20

Figure 1 – Angles of incidence, divergence, reflection and acceptance . 9

Table 1 – Different cases related to reflectance nomenclature. . 9
Table 2 – Range and weight of the different UV classes, calculated with the full data
set from IEC 60904-3 . 14
Table 3 – Wavelength range, depending on the type of the desired average . 14

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Solar thermal electric plants -
Part 3-5: Laboratory reflectance measurement of solar reflectors

FOREWORD
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IEC 62862-3-5 has been prepared by IEC technical committee TC 117: Solar thermal electric
plants. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
117/253/FDIS 117/255/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
A list of all parts in the IEC 62862 series, published under the general title Solar thermal electric
plants, can be found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
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The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
1 Scope
This document specifies laboratory methods to measure reflectance of all types of reflectors for
use in concentrating solar thermal (CST) plants.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60904-3, Photovoltaic devices - Part 3: Measurement principles for terrestrial photovoltaic
(PV) solar devices with reference spectral irradiance data
IEC TS 62862-1-1, Solar thermal electric plants - Part 1-1: Terminology
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
ISO 4628-2:2016, Paints and varnishes — Evaluation of degradation of coatings — Designation
of quantity and size of defects, and of intensity of uniform changes in appearance — Part 2:
Assessment of degree of blistering
ISO 9488:2022, Solar energy — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9488:2022, IEC TS
62862-1-1 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1 Solar definitions
3.1.1
direct solar radiation
G
b
solar radiation incident on a given plane, and originating from a small solid angle centred on
the sun's disk
[SOURCE: ISO 9488:2022 [1], 3.2.17.]
3.2 Collector components
3.2.1
reflector
optical device made of several materials, suitably chosen and arranged to make a surface with
proper reflectance (3.4.1) features
Note 1 to entry: The term "mirror" is typically used as a synonym of reflector.
3.3 Angle definitions
3.3.1
angle of incidence
incidence angle
incident angle
θ
i
angle between the line connecting the center of the light source (solar disc or the light source
of the measurement equipment) to a point on an irradiated surface, and the normal to that
surface at the same point
Note 1 to entry: Unit: the non-SI unit is degrees.
Note 2 to entry: SEE: Figure 1.
[SOURCE: IEC TS 62862-1-1:2018 [2], 3.2.3, modified - The subscript "i" is added to the symbol
and the type of light source is broadened.]
3.3.2
divergent angle
angle of divergence
φ
i
half-apex angle of the cone that encloses the bundle of light rays illuminating a specific point
on the reflector (3.2.1)
Note 1 to entry: Unit: the non-SI unit is mrad.
Note 2 to entry: SEE: Figure 1.
3.3.3
angle of reflection
reflection angle
θ
r
angle between the normal to the irradiated surface at a given point and the reflected ray
Note 1 to entry: SEE: Figure 1.
Note 2 to entry: For specular reflection, the incidence ray, normal and reflected ray lie in the same plane, and the
( )
angle of reflection equals the angle of incidence (3.3.1) 𝜃𝜃 =𝜃𝜃 .
𝑟𝑟 𝑖𝑖
Note 3 to entry: Owing to the divergence of solar radiation and surface irregularities, the reflected radiation can be
distributed within a cone centered around the specular reflection direction.
3.3.4
angle of acceptance
acceptance angle
φ
half-apex angle of the cone containing the rays reflected at a given point of the reflector (3.2.1)
and intercepted by the receiving surface (detector of measurement device or receiver of CST
system)
Note 1 to entry: Unit: the non-SI unit is mrad.
Note 2 to entry: SEE: Figure 1.
Note 3 to entry: This angle depends on the geometry (size, distance, etc.) of the reflector (3.2.1) and the receiving
surface.
3.4 Optical properties
3.4.1
reflectance
ρ(P , P , P , P , P )
λ θi φi φ Ts
ratio of the radiant flux reflected from a surface to that of the incident radiation
Note 1 to entry: The reflectance is a dimensionless variable ranging from 0 to 1.
Note 2 to entry: The reflectance depends on five parameters, named as P and a subscript which refers to the
specific parameter influencing the reflectance. These parameters are P , P , P , P and P , and shall be indicated
λ θi φi φ Ts
in parentheses after ρ. P refers to the influence of the wavelength, λ. Four types of reflectance are defined in relation
λ
to P (see spectral reflectance (3.4.2) to UV reflectance (3.4.5)). P refers to the angle of the incident light source,
λ θi
θ. One special case is defined in relation to P (see near-normal reflectance (3.4.6)); in other cases, the specific
i θi
value of θ shall be indicated. P refers to the divergent angle (3.3.2) of the incident radiation, φ . One special case
i φi i
is defined in relation to P (see sun-conic reflectance (3.4.8)); in other cases, the specific value of φ shall be indicated
φi i
(see conic reflectance (3.4.7)). P refers to the dependence of the reflectance on angle of acceptance (3.3.4)
φ
considered, φ. One special case (see specular reflectance (3.4.9)) and three types of reflectance (see near-specular
reflectance (3.4.10) to diffuse reflectance (3.4.12)) are defined in relation to P . P refers to the influence of the
φ Ts
temperature of the surface in which the radiation is falling on, T . Table 1 summarizes the different cases.
s
SEE: Table 1.
Note 3 to entry: Unless otherwise specified, the temperature T taken into consideration is the ambient temperature.
s
In this case, P can be omitted and only the first 4 parameters are indicated in parentheses.
Ts
Note 4 to entry: Talking about optical properties of materials used in solar applications (reflectance in this particular
case) only the ending "-ance" is permitted, because it means the amount of such a feature; that amount can be
degraded by the thermal process, soiling, mechanical damage, etc.
Note 5 to entry: To properly refer to the reflectance, the different options for the four/five parameters in parentheses
(see spectral reflectance (3.4.2) to diffuse reflectance (3.4.12)) shall be mentioned sequentially. Example: "SW"
means solar-weighted, "n" means near-normal, "sc" means sun-conic and "φ" means near-specular; therefore,
ρ(SW,n,sc,φ) is the solar-weighted near-normal sun-conic near-specular reflectance (3.4.10), measured at ambient
temperature.
Note 6 to entry: The first time that the reflectance is mentioned in a document, the value(s) of the four/five
parameters in parentheses (or the corresponding symbol(s) or letter(s) for the special cases) as well as the full name
shall be specified. For the rest of the document, the parameters in parentheses may be substituted by the
corresponding subscripts, provided that it is clearly stated in the text. For example, ρ(SW,n,sc,φ) may be named in
ρ . Also, using equivalent short names with the most representative parameters is
the rest of the document as
s,φ
allowed, provided that it is clearly stated in the text. For example, the "solar-weighted near-normal sun-conic near-
specular reflectance (3.4.10)" may be named as the "solar specular reflectance".
3.4.2
spectral reflectance
ρ({λ ,…, λ },P ,P ,P ,P )
1 i θi φi φ Ts
ρ([λ λ ],P ,P ,P ,P )
a, b θi φi φ Ts
reflectance (3.4.1) values measured across a specified wavelength range
Note 1 to entry: The wavelength range can be discrete, represented as a set of wavelengths, {λ ,…,λ}; or
1 i
continuous, represented by an interval [λ , λ ], with measurements taken at step of a few nanometres or less.
a b
Note 2 to entry: The values of the wavelengths used for the measurement shall be given the first time that it is
mentioned in a document. For the rest of the document, the symbols {λ ,…,λ } or [λ , λ ] can be used.
1 i a b
λ , λ ], the wavelength step within such
Note 3 to entry: When the wavelengths interval is given in a range, that is [
a b
range shall be indicated in the text.
3.4.3
monochromatic reflectance
single wavelength reflectance
ρ(λ,P ,P ,P ,P )
θi φi φ Ts
reflectance (3.4.1) measured at a single wavelength, λ, within a defined wavelength range, ∆λ,
centred at λ
Note 1 to entry: The value of the wavelength used for the measurement shall be given the first time that it is
mentioned in a document. For the rest of the document, the symbol λ can be used.
Note 2 to entry: The ∆λ depends on the optics of the measurement equipment and shall be specifically indicated in
the text.
3.4.4
solar reflectance
solar-weighted reflectance
ρ(SW,P ,P ,P ,P )
θi φi φ Ts
spectral reflectance (3.4.2) spectrum weighted over the solar spectrum
Note 1 to entry: See 6.2 for the method to calculate the solar reflectance, with the spectrum from IEC 60904-3 [3].
Note 2 to entry: If several solar spectra are used to calculate the solar reflectance, it shall be indicated with a
number in subscript (SW , SW , …) and the meaning of the different options shall be clearly indicated in the text (or
1 2
in the table foot).
3.4.5
UV reflectance
UV-weighted reflectance
ρ(UVW,P ,P ,P ,P )
θi φi φ Ts
spectral reflectance (3.4.2) spectrum weighted over the ultraviolet (UV) range of the solar
spectrum
Note 1 to entry: See 6.3 for the method to calculate the UV reflectance.
Note 2 to entry: If several UV parts are used to calculate the UV reflectance, it shall be indicated (UVAW, UVBW
…).
3.4.6
near-normal reflectance
ρ(P ,n,P ,P ,P )
λ φi φ Ts
reflectance (3.4.1) measured when the incidence angle (3.3.1) is sufficiently small so that the
reflectance (3.4.1) differs from the value measured at normal incidence by less than the
measurement error
Note 1 to entry: Although the letter "n" can be used for the parameter P to simplify the nomenclature when this
θi
condition for near-normal is accomplished, the specific value of the θ shall be indicated in the text.
i
Note 2 to entry: Typically, the incidence angle (3.3.1) is considered "near-normal" if it is less than or equal to 20°.
3.4.7
conic reflectance
ρ(P ,P ,φ ,P ,P )
λ θi i φ Ts
reflectance (3.4.1) when the divergent angle (3.3.2) of the incident radiation is greater than zero
3.4.8
sun-conic reflectance
ρ(P ,P ,sc,P ,P )
λ θi φ Ts
conic reflectance (3.4.7) when the divergent angle (3.3.2) of the incidence radiation is equal to
the mean value of the divergent angle (3.3.2) of the solar radiation on Earth under clear sky
conditions, typically 4,7 mrad
3.4.9
specular reflectance
ρ(P ,P ,P ,0,P )
λ θi φi Ts
ratio of the radiant flux incident on a surface as parallel beams (i.e. a plane wave), to the radiant
flux reflected by the surface in the specular direction, also as a plane wave (φ = 0)
Note 1 to entry: Specular reflectance is a theoretical parameter that can only be obtained through modeling, since
real light source emits radiation with divergence angles, and the detectors of measurement devices have finite
acceptance angles.
Note 2 to entry: The specular direction is on the same plane as the incident radiation and the normal to the surface,
making an angle equal to the incidence one, in the opposite direction.
Note 3 to entry: The divergent angle (3.3.2) does not apply when the specular reflectance is referred. Therefore, in
this case "0" shall be indicated in P . That is, specular reflectance shall be named as ρ(P ,P ,0,0,P ).
φi λ θi Ts
3.4.10
near-specular reflectance
ρ(P ,P ,P ,φ,P )
λ θi φi Ts
specular reflectance (3.4.9) when the acceptance angle (3.3.4) is not null (φ > 0)
Note 1 to entry: Near-specular reflectance can be named as specular reflectance (3.4.9) for simplification, once it
is clearly indicated in the text, to avoid confusion with the case of φ = 0.
3.4.11
hemispherical reflectance
ρ(P ,P ,P ,h,P )
λ θi φi Ts
ratio of the total radiant flux reflected and diffused by a surface across the entire hemisphere
above it, to the total radiant flux incident on the surface
Note 1 to entry: The divergent angle (3.3.2) does not apply when the hemispherical reflectance is measured.
Therefore, in this case "-" shall be indicated in P . That is, the hemispherical reflectance shall be named as ρ(P ,P ,-
φi λ θi
,h,P ).
Ts
3.4.12
diffuse reflectance
ρ(P ,P ,P ,d,P )
λ θi φi Ts
ratio of the radiant flux diffusely reflected by a surface across the entire hemisphere above it,
excluding the flux reflected within the solid angle 2πφ around the specular direction, to the total
radiant flux incident on the surface
Note 1 to entry: The diffuse reflectance is equal to the hemispherical reflectance (3.4.11) minus the specular
reflectance (3.4.9).
3.4.13
specularity
χ
ratio between near-specular reflectance (3.4.10) and hemispherical reflectance (3.4.11)
3.5 Figures and tables
Key
incidence angle
θ
i
specular reflectance angle
θ
r
angle of divergence of the incidence radiation
φ
i
angle of acceptance of specular reflectance
φ
1 reflecting surface
2 light source
Figure 1 – Angles of incidence, divergence, reflection and acceptance
Table 1 – Different cases related to reflectance nomenclature.
Parameter affecting a Section Nomenclature
Symbol
reflectance
spectral Spectral reflectance
ρ({λ ,.,λ }, P , P ,P ,P );
1 i θi φi φ Ts
reflectance
ρ([λ ,λ ], P , P , P ,P )
a b θi φi φ Ts
monochrom Monochromatic reflectance
ρ(λ, P , P , P , P )
θi φi φ Ts
atic
P
λ
reflectance
solar Solar reflectance, solar-weighted
ρ(SW, P , P , P , P )
θi φi φ Ts
reflectance reflectance
UV UV reflectance, UV-weighted
ρ(UVW, P , P , P , P )
θi φi φ Ts
reflectance reflectance
near-normal Near-normal reflectance
ρ(P , n, P , P ,P )
λ φi φ Ts
reflectance
P
θi
---
ρ(P , θ , P , P ,P ) Reflectance at a certain θ , different
λ i φi φ Ts i
from near-normal
conic Conic reflectance
ρ(P , P ,φ ,P ,P )
λ θi i φ Ts
reflectance
P
φi
sun-conic Sun-conic reflectance
ρ(P , P , sc, P ,P )
λ θi φ Ts
reflectance
specular Specular reflectance
ρ(P , P , P , 0, P )
P λ θi φi Ts
φ
reflectance
Parameter affecting a Section Nomenclature
Symbol
reflectance
near- Near-specular reflectance
ρ(P , P , P , φ, P )
λ θi φi Ts
specular
reflectance
hemispheric
ρ(P , P , P , h, P ) Hemispherical reflectance
λ θi φi Ts
al
reflectance
ρ(P , P , P , d , P ) diffuse Diffuse reflectance
λ θi φi Ts
reflectance
a
The specific parameter affecting the reflectance that is addressed in each case is marked in bold type.
4 Preparation of measurement
4.1 Sampling
The following rules shall be followed to prepare the reflector samples before they are measured.
– Unless the instrument is able to measure curved samples or the curvature of the sample is
so small that the measurement result is not affected by it, the samples shall be cut to a size
that allows measurement on different points on the surface but also fits into the instru
...