How to find the reflectance of light. Light reflectance on colored surfaces. Solar absorption coefficient
Light on collision with reflective surface.
It lies in the fact that and falling, and reflected Ray placed in a single plane with a perpendicular to the surface, and this perpendicular divides the angle between the indicated rays into identical components.
More often it is simplified as follows: injection fall and angle light reflections the same:
α = β.
The law of reflection is based on features wave optics... It was experimentally substantiated by Euclid in the 3rd century BC. It can be considered a consequence of the use of Fermat's principle for mirror surface... Also, this laws can be formulated as a consequence of the Huygens principle, according to which any point of the environment, to which the indignation has reached, acts as a source secondary waves.
Any environment specifically reflects and absorbs light emission... The parameter describing the reflectivity of the surface of a substance is denoted as reflection coefficient(ρ orR) ... Quantitatively, the reflection coefficient is equal to the ratio radiation flux reflected by the body to the stream hitting the body:
Light is completely reflected from a thin film of silver or liquid mercury deposited on a sheet of glass.
Allocate diffuse and mirror reflection.
The distribution of currents and voltages in a long line is determined not only by the wave parameters that characterize the intrinsic properties of the line and do not depend on the properties of the circuit sections external to the line, but also by the reflection coefficient of the line, which depends on the degree of matching of the line with the load.
Complex reflectivity of a long line is the ratio of the complex effective values of the voltages or currents of the reflected and incident waves in an arbitrary section of the line:
For determining p (x) it is necessary to find the integration constants A and A 2, which can be expressed in terms of currents and voltages at the beginning (x = 0) or end (x =/) lines. Let at the end of the line (see Fig. 8.1) the line voltage
and 2 = u (l y t) = u (x, t) x = i, and her current i 2 = /(/, t) = i (x, t) x = [. Denoting the complex effective values of these quantities through U 2 = 0 (1) = U (x) x = i = and 2 and / 2 = / (/) = I (x) x = i = i 2 and setting in expressions (8.10), (8.11 ) x = I, we get
Substituting formulas (8.31) into relations (8.30), we express the reflection coefficient in terms of the current and voltage at the end of the line:
where x "= I - x - distance measured from the end of the line; p 2 = p (x) |, = / = 0 neg (x) / 0 pal (x) x = 1 = 02 - Zj 2) / (U 2 + Zj 2) - reflection coefficient at the end of a line, the value of which is determined only by the ratio between the load resistance Z u = U 2 / i 2 and the characteristic impedance of the Z B line:
Like any complex number, the reflectance of a line can be represented in exponential form:
Analyzing expression (8.32), we establish that the modulus of the reflection coefficient
increases smoothly with growth NS and reaches the highest value p max (x)= | p 2 | at the end of the line.
Expressing the reflection coefficient at the beginning of the line p ^ through the reflection coefficient at the end of the line p 2
we find that the modulus of the reflection coefficient at the beginning of the line at e 2a1 times less than the modulus of the reflection coefficient at its end. From expressions (8.34), (8.35) it follows that the modulus of the reflection coefficient of a homogeneous line without losses has the same value in all sections of the line.
Using formulas (8.31), (8.33), the voltage and current in an arbitrary section of the line can be expressed in terms of the voltage or current and the reflection coefficient at the end of the line:
Expressions (8.36) and (8.37) allow us to consider the distribution of voltages and currents in a uniform long line in some typical modes of its operation.
Traveling waves mode. Traveling wave mode the mode of operation of a homogeneous line is called, in which only an incident voltage and current wave propagates in it, i.e. the amplitudes of the voltage and current of the reflected wave in all sections of the line are equal to zero. Obviously, in the regime of traveling waves, the reflection coefficient of the line is p (xr) = 0. From expression (8.32) it follows that the reflection coefficient p (r) can be zero either in a line of infinite length (at 1 = oo the incident wave cannot reach the end of the line n to be reflected from it), or in a line of finite length, the load resistance of which is chosen in such a way that the reflection coefficient at the end of the line p 2 = 0. Of these cases, only the second is of practical interest, for the implementation of which, as follows from expression (8.33), it is necessary that the load resistance of the line be equal to the characteristic impedance Z lt (such a load is called agreed).
Assuming in expressions (8.36), (8.37) p 2 = 0, we express the complex effective values of voltage and current in an arbitrary section of the line in the traveling wave mode through the complex effective values of the voltage 0 2
and current / 2 at the end of the line: 
Using expression (8.38), we find the complex effective values of voltage and current at the beginning of the line:
Substituting equality (8.39) into relations (8.38), we express the voltage and current in an arbitrary section of the line in the mode of traveling waves through the voltage and current at the beginning of the line:
Let's represent the voltage and current at the beginning of the line in exponential form: Ui = G / 1 e; h D = Let's move from the complex effective values of voltage and current to instantaneous ones:
As follows from expressions (8.41), in the mode of traveling wills, the amplitudes of the voltage and current in the line with losses(a> 0) decrease exponentially with increasing x, and in a lossless line(a = 0) keep the same value in all sections of the line(fig. 8.3).
The initial phases of voltage y (/) - p.g and current v | / (| - p.g in the mode of traveling waves vary along the line according to a linear law, and the phase shift between voltage and current in all sections of the line has the same value i | / M - y, y
The input impedance of the line in the traveling wave mode is equal to the wave impedance of the line and does not depend on its length:
In a lossless line, the characteristic impedance is purely resistive. (8.28), therefore, in the traveling wave mode, the phase shift between voltage and current in all sections of the line without losses is equal to zero(y;
Instantaneous power consumed by a section of a line without losses located to the right of an arbitrary section NS(see Fig. 8.1), is equal to the product of instantaneous values of voltage and current in the section NS.
Rice. 83.
From expression (8.42) it follows that the instantaneous power consumed by an arbitrary section of the line without losses in the traveling wave mode cannot be negative, therefore, in the mode of running wills, energy is transmitted in the line only in one direction - from the energy source to the load.
There is no energy exchange between the source and the load in the traveling wave mode, and all the energy transferred by the incident wave is consumed by the load.
Standing wave mode. If the load resistance of the line in question is not equal to the characteristic impedance, then only part of the energy transferred by the incident wave to the end of the line is consumed by the load. The rest of the energy is reflected from the load and returns to the source in the form of a reflected wave. If the modulus of the reflection coefficient of the line | p (.r) | = 1, i.e. the amplitudes of the reflected and incident waves in all sections of the line are the same, then a specific mode is established in the line, called standing wave mode. According to expression (8.34), the modulus of the reflection coefficient | p (lg) | = 1 only if the modulus of the reflection coefficient at the end of the line | p 2 | = 1, and the line attenuation coefficient a = 0. Analyzing expression (8.33), one can make sure that | р 2 | = 1 only in three cases: when the load resistance is either zero or infinity, or has a purely reactive character.
Hence, the standing wave mode can be established only in the line without losses in case of short circuit or no-load at the output, and, if the load resistance at the line output is purely reactive.
With a short circuit at the line output, the reflection coefficient at the end of the line p 2 = -1. In this case, the voltages of the incident and reflected waves at the end of the line have the same amplitudes, but are shifted in phase by 180 °, so the instantaneous value of the voltage at the output is identically zero. Substituting in expressions (8.36), (8.37) p 2 = - 1, y = ur, Z B = /? „, We find the complex effective values of the voltage and current of the line:
Assuming that the initial phase of the current /? at the output of the line is equal to zero, and passing from the complex effective values of voltages and currents to instantaneous
we establish that with a short circuit at the output of the line, the amplitudes of voltage and current change along the line according to the periodic law
taking maximum values at individual points of the line U m check = V2 I m max = V2 / 2 and vanishing at some other points (Fig. 8.4).
It is obvious that at those points of the line at which the amplitude of the voltage (current) is zero, the instantaneous values of the voltage (current) are identically zero. Such points are called nodes of voltage (current).
The characteristic points at which the amplitude of the voltage (current) takes on a maximum value are called antinodes of voltage (current). As is obvious from Fig. 8.4, voltage nodes correspond to current antinodes and, conversely, current nodes correspond to voltage antinodes.
Rice. 8.4. Distribution of voltage amplitudes(a) and current(b) along the line in the mode short circuit
Rice. 8.5. Distribution of instantaneous voltage values (a) and current (b) along the line in short circuit mode
The distribution of instantaneous voltage and current values along the line (Fig. 8.5) obeys a sinusoidal or cosine law, however, over time, the coordinates of points with the same phase remain unchanged, i.e. voltage and current waves seem to "stand still". That is why this line operation mode was named standing wave mode.
The coordinates of the stress nodes are determined from the condition sin px /, = 0, whence
where To= 0, 1,2, ..., and the coordinates of the voltage antinodes are from the condition cos p.r "(= 0, whence
where NS = 0, 1,2,...
In practice, it is convenient to measure the coordinates of nodes and antinodes from the end of the line in fractions of the wavelength X. Substituting relation (8.21) into expressions (8.43), (8.44), we obtain x "k = kX / 2, x "„ = (2 n + 1) X / 4.
Thus, the nodes of voltage (current) and antinodes of voltage (current) alternate with an interval X / 4, and the distance between neighboring nodes (or antinodes) is equal to X / 2.
Analyzing the expressions for the voltage and current of the incident and reflected waves, it is easy to make sure that voltage antinodes arise in those sections of the line in which the voltages of the incident and reflected waves coincide in phase and, therefore, are summed, and the nodes are located in sections where the voltages of the incident and reflected waves are in antiphase and, therefore, are subtracted. Instantaneous power consumed by an arbitrary section of the line varies in time according to a harmonic law
therefore, the active power consumed by this section of the line is zero.
Thus, in the mode of standing will, energy is not transferred along the line, and at each section of the line, only energy is exchanged between the electric and magnetic fields.
Similarly, we find that in the no-load mode (p2 = 1) the distribution of voltage (current) amplitudes along the line without losses (Fig.8.6)
has the same character as the distribution of the amplitudes of the current (voltage) in the short-circuit mode (see Fig. 8.4).
Consider a lossless line, the load resistance at the output of which is purely reactive:
Rice. 8.6. Distribution of voltage amplitudes (a) and current (b) along the line in idle mode
Substituting formula (8.45) into expression (8.33), we obtain
From expression (8.46) it follows that with a purely reactive load, the modulus of the reflection coefficient at the line output | p 2 | = 1, and the values of the argument p p2 at finite values x n lie between 0 and ± l.
Using expressions (8.36), (8.37) and (8.46), we find the complex effective values of the line voltage and current:
where φ = arctan (/? B / x „). From expression (8.47) it follows that the amplitudes of voltage and current change along the line according to the periodic law:
and the coordinates of voltage nodes (current antinodes) x "k = (2k + 1)7/4 + 1y where 1 = f7 / (2tg); k= 0, 1, 2, 3, ..., and the coordinates of voltage antinodes (current nodes) NS"" = PC/2 + 1, where NS = 0, 1,2,3,...
The distribution of the voltage and current amplitudes at a purely reactive load in general has the same character as in the no-load or short-circuit modes at the output (Figure 8.7), and all nodes and all antinodes are displaced by an amount 1 L so that at the end of the line there is neither a node nor an antinode of current or voltage.
With capacitive load -k / A 0, so the first voltage node will be at a distance less than to / A from the end of the line (fig. 8.7, a); at inductive load 0 t K / A the first node will be located at a distance greater than 7/4, but less To/ 2 from the end of the line (Fig.8.7, b).
Mixed wave mode. The modes of traveling and standing waves are two limiting cases, in one of which the amplitude of the reflected wave in all sections of the line is equal to zero, and in the other, the amplitudes of the incident and reflected waves in all sections of the line are the same. In os-
Rice. 8.7. Distribution of voltage amplitudes along the line with the capacitive(a) and inductive
In other cases, there is a mixed wave mode in the line, which can be considered as a superposition of traveling and standing wave modes. In mixed wave mode, the energy transmitted by the incident wave to the end of the line is partially absorbed by the load and partially reflected from it, therefore the amplitude of the reflected wave is greater than zero, but less than the amplitude of the incident wave.
As in the standing wave mode, the distribution of the voltage and current amplitudes in the mixed wave mode (Fig.8.8)
Rice. 8.8. Distribution of voltage amplitudes (a ) and current(b) along the line in mixed wave mode with a purely resistive load(R „> R H)
has distinct highs and lows, repeating through X / 2. However, the amplitudes of the current and voltage at the minima are not equal to zero.
The smaller part of the energy is reflected from the load, i.e. the higher the degree of matching of the line with the load, the less pronounced the maxima and minima of voltage and current, therefore the ratio between the minimum and maximum values of the amplitudes of voltage and current can be used to assess the degree of matching of the line with the load. A value equal to the ratio of the minimum and maximum values of the amplitude of the voltage or current is called traveling wave coefficient(KBV)
KBV can vary from 0 to 1, and, the more К () У, the closer the line operation mode is to the running will mode.
It is obvious that at the points of the line at which the amplitude of the voltage (current) reaches its maximum value, the voltages (currents) of the incident and reflected waves coincide in phase, and where the amplitude of the voltage (current) has a minimum value, the voltages (currents) of the incident and reflected waves waves are in antiphase. Hence,
Substituting expression (8.49) into relations (8.48) and taking into account that the ratio of the amplitude of the voltage of the reflected wave to the amplitude of the voltage of the incident wave is the modulus of the reflection coefficient of the line | p (xr) |, we establish a relationship between the coefficient of the traveling wave and the coefficient of reflection:
In a lossless line, the modulus of the reflection coefficient in any section of the line is equal to the modulus of the reflection coefficient at the end of the line, therefore, the coefficient of the traveling wave in all sections of the line has the same value: Ks> =
= (1-NYO + N).
In a line with losses, the modulus of the reflection coefficient changes along the line, reaching the highest value at the point of reflection (at NS= /). In this regard, in a line with losses, the coefficient of the traveling wave changes along the line, taking a minimum value at its end.
Along with KBV, to assess the degree of line matching with the load, its inverse value is widely used - standing wave ratio(SWR):
In the traveling wave mode, K c = 1, and in the mode of standing waves K s-? oo.
When passing through the interfaces between the media, acoustic waves experience not only reflection and refraction, but also the transformation of waves of one type into another. Let us consider the simplest case of normal incidence of a wave on the boundary of two extended media (Fig. 3.1). In this case, there is no wave transformation.
Consider the energy relationships between the incident, reflected and transmitted waves. They are characterized by the coefficients of reflection and refraction.
Amplitude reflection coefficient is the ratio of the amplitudes of the reflected and incident waves:
Amplitude transmission coefficient the ratio of the amplitudes of the transmitted and incident waves is called:
These coefficients can be determined by knowing the acoustic characteristics of the media. When a wave falls from medium 1 into medium 2, the reflection coefficient is determined as
, (3.3)
where, are the acoustic impedances of media 1 and 2, respectively.
When a wave falls from medium 1 into medium 2, the transmission coefficient is denoted and defined as
. (3.4)
When a wave falls from medium 2 into medium 1, the transmission coefficient is denoted and defined as
. (3.5)
It can be seen from formula (3.3) for the reflection coefficient that the more the acoustic impedances of the media differ, the greater part of the energy of the sound wave will be reflected from the interface between the two media. This determines both the possibility and the efficiency of detecting violations of the continuity of the material (inclusions of the medium with acoustic resistance that differs from the resistance of the controlled material).
It is because of the differences in the values of the reflection coefficients that slag inclusions are detected much worse than defects of the same size, but with air filling. Reflection from a gas-filled discontinuity approaches 100%, and for a slag-filled discontinuity, this coefficient is much lower.
At normal incidence of a wave on the boundary of two extended media, the ratio between the amplitudes of the incident, reflected and transmitted waves is
. (3.6)
The energy of the incident wave in the case of normal incidence on the boundary of two extended media is distributed between the reflected and transmitted waves according to the conservation law.
In addition to the reflection and amplitude transmission coefficients, the reflection and intensity transmission coefficients are also used.
Intensity reflectance is the ratio of the intensities of the reflected and incident waves. At normal incidence of the wave
, (3.7)
where is the reflection coefficient when falling from medium 1 to medium 2;
Is the reflection coefficient when falling from medium 2 to medium 1.
Intensity transmission coefficient- the ratio of the intensities of the transmitted and incident waves. When the wave falls along the normal
, (3.8)
where is the transmission coefficient when falling from medium 1 to medium 2;
- coefficient of transmission when falling from medium 2 to medium 1.
The direction of incidence of the wave does not affect the values of the reflection and intensity transmission coefficients. The law of conservation of energy through the reflection and transmission coefficients is written as follows
With an oblique incidence of a wave on the interface between the media, the transformation of a wave of one type into another is possible. The processes of reflection and transmission in this case are characterized by several coefficients of reflection and transmission, depending on the type of incident, reflected and transmitted waves. The reflection coefficient in this form has the designation (- an index indicating the type of the incident wave, - an index indicating the type of the reflected wave). Cases are possible,. The transmission coefficient is indicated by (- an index indicating the type of the falling wave, - an index indicating the type of the transmitted wave). Cases are possible, and.
Transmittance
reflection coefficient
and absorption coefficient
The coefficients t, r and a depend on the properties of the body itself and the wavelength of the incident radiation. Spectral dependence, i.e. the dependence of the coefficients on the wavelength determines the color of both transparent and opaque (t = 0) bodies.
According to the law of conservation of energy
F neg + F absorb + F pr =. (eight)
Dividing both sides of the equality by, we get:
r + a + t = 1. (9)
A body for which r = 0, t = 0, a = 1 is called absolutely black .
An absolutely black body at any temperature completely absorbs all the energy of radiation of any wavelength incident on it. All real bodies are not completely black. However, some of them in certain wavelength intervals are close in their properties to a blackbody. For example, in the region of visible light wavelengths, the absorption coefficients of soot, platinum black and black velvet differ little from unity. The most perfect model of a black body can be a small hole in a closed cavity. Obviously, this model is the closer in characteristics to a black body, the greater the ratio of the surface area of the cavity to the area of the hole (Fig. 1).
The spectral characteristic of the absorption of electromagnetic waves by the body is spectral absorption coefficient a l is the value determined by the ratio of the radiation flux absorbed by the body in a small spectral interval (from l to l + d l) to the flux of incident radiation in the same spectral interval:
.
(10)
The emissivity and absorptivity of an opaque body are interrelated. The ratio of the spectral density of the energy luminosity of the equilibrium radiation of a body to its spectral absorption coefficient does not depend on the nature of the body; for all bodies, it is a universal function of wavelength and temperature ( Kirchhoff's law ):
. (11)
For a black body, a l = 1. Therefore, it follows from Kirchhoff's law that M e, l = , i.e. the universal Kirchhoff function is the spectral density of the radiant luminosity of a black body.
Thus, according to Kirchhoff's law, for all bodies, the ratio of the spectral density of the radiant luminosity to the spectral absorption coefficient is equal to the spectral density of the radiant luminosity of an absolutely black body at the same values T and l.
It follows from Kirchhoff's law that the spectral density of the radiant luminosity of any body in any region of the spectrum is always less than the spectral density of the radiant luminosity of an absolutely black body (at the same wavelength and temperature). In addition, it follows from this law that if the body at a certain temperature does not absorb electromagnetic waves in the interval from l to l + d l, then it does not emit them in this range of lengths at a given temperature.
Analytical view of the function for a black body
was established by Planck on the basis of quantum concepts of the nature of radiation:
(12)
The emission spectrum of an absolutely black body has a characteristic maximum (Fig. 2), which, with increasing temperature, shifts to the short-wavelength part (Fig. 3). The position of the maximum spectral density of the radiant luminosity can be determined from expression (12) in the usual way, equating the first derivative to zero:
. (13)
Denoting, we get:
NS – 5 ( – 1) = 0. (14)
Rice. Fig. 2 3
The numerical solution of this transcendental equation gives
NS = 4, 965.
Hence,
, (15)
= = b 1 = 2.898 m K, (16)
Thus, the function reaches a maximum at a wavelength inversely proportional to the thermodynamic temperature of a black body ( Wine's first law ).
It follows from Wien's law that at low temperatures, predominantly long (infrared) electromagnetic waves are emitted. As the temperature rises, the proportion of radiation in the visible region of the spectrum increases, and the body begins to glow. With a further increase in temperature, the brightness of its glow increases, and the color changes. Therefore, the color of the radiation can serve as a characteristic of the radiation temperature. An approximate dependence of the glow color of a body on its temperature is given in table. 1.
Table 1
Wine's first law is also called displacement law , thereby emphasizing that with increasing temperature, the maximum of the spectral density of the radiant luminosity shifts towards shorter wavelengths.
Substituting formula (17) into expression (12), it is easy to show that the maximum value of the function is proportional to the fifth power of the thermodynamic temperature of the body ( Wine's second law ):
The energy luminosity of an absolutely black body can be found from expression (12) by simple integration over the wavelength
(18)
where is the reduced Planck constant,
The energetic luminosity of a black body is proportional to the fourth power of its thermodynamic temperature. This provision is called Stephen-Boltzmann law , and the proportionality coefficient s = 5.67 × 10 -8 – Stefan - Boltzmann constant.
A black body is an idealization of real bodies. Real bodies emit radiation, the spectrum of which is not described by Planck's formula. Their energetic luminosity, in addition to temperature, depends on the nature of the body and the state of its surface. These factors can be taken into account if a coefficient is introduced into formula (19), which shows how many times the energy luminosity of an absolutely black body at a given temperature is greater than the energy luminosity of a real body at the same temperature
whence, or (21)
For all real bodies<1 и зависит как от природы тела и состояния его поверхности, так и от температуры. В частности, для вольфрамовых нитей электроламп накаливания зависимость от T has the form shown in Fig. 4.
The measurement of the radiation energy and temperature of the electric furnace is based on Seebeck effect, consisting in the emergence of an electromotive force in an electrical circuit consisting of several dissimilar conductors, the contacts of which have different temperatures.
Two dissimilar conductors form thermocouple , and series-connected thermocouples are a thermal column. If the contacts (usually junctions) of the conductors are at different temperatures, then in a closed circuit, including thermocouples, a thermoEMF arises, the value of which is uniquely determined by the temperature difference between hot and cold contacts, the number of thermocouples connected in series and the nature of the conductor materials.
The magnitude of the thermoEMF arising in the circuit due to the energy of the radiation incident on the junction of the thermal column is measured by a millivoltmeter located on the front panel of the measuring device. The scale of this device is graduated in millivolts.
The temperature of a black body (furnace) is measured using a thermoelectric thermometer, consisting of one thermocouple. Its EMF is measured by a millivoltmeter, also located on the front panel of the measuring device and calibrated in ° C.
Note. The millivoltmeter records the temperature difference between the hot and cold junctions of the thermocouple, therefore, to obtain the furnace temperature, it is necessary to add the value of the room temperature to the reading of the device.
In this work, the thermopower of the thermopile is measured, the value of which is proportional to the energy spent on heating one of the contacts of each thermocouple of the column, and, therefore, to the radiant luminosity (with equal time intervals between measurements and a constant emitter area):
where b- coefficient of proportionality.
Equating the right-hand sides of equalities (19) and (22), we obtain:
s × T 4 =b× e,
where with- constant value.
Simultaneously with the measurement of the thermoEMF of the thermal column, the temperature difference Δ t hot and cold junctions of a thermocouple placed in an electric furnace, and determine the temperature of the furnace.
Using the experimentally obtained values of the temperature of an absolutely black body (furnace) and the corresponding values of the thermoEMF of the thermal column, the value of the coefficient of proportional
sti with, which should be the same in all experiments. Then build a graph of dependence c = f (T), which should look like a straight line parallel to the temperature axis.
Thus, in laboratory work, the nature of the dependence of the energy luminosity of an absolutely black body on its temperature is established, i.e. the Stefan – Boltzmann law is verified.
GOST R 56709-2015
NATIONAL STANDARD OF THE RUSSIAN FEDERATION
BUILDINGS AND CONSTRUCTIONS
Methods for measuring light reflectance by surfaces of rooms and facades
Buildings and structures. Methods for measuring reflectance of rooms and fronts surfaces
Introduction date 2016-05-01
Foreword
1 DEVELOPED by the Federal State Budgetary Institution "Research Institute of Building Physics of the Russian Academy of Architecture and Building Sciences" ("NIISF RAASN") with the participation of the Limited Liability Company "CERERA-EXPERT" ("CERERA-EXPERT" LLC)
2 INTRODUCED by the Technical Committee for Standardization TC 465 "Construction"
3 APPROVED AND PUT INTO EFFECT by the Order of the Federal Agency for Technical Regulation and Metrology of November 13, 2015 N 1793-st
4 INTRODUCED FOR THE FIRST TIME
The rules for the application of this standard are set out in GOST R 1.0-2012 (section 8). Information on changes to this standard is published in the annual (as of January 1 of the current year) information index "National Standards", and the official text of changes and amendments is published in the monthly information index "National Standards". In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the next issue of the monthly information index "National Standards". Relevant information, notice and texts are also posted in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet (www.gost.ru)
1 area of use
1 area of use
This International Standard specifies methods for measuring the integral, diffuse and specular reflection coefficients of light by materials used for decoration of premises and facades of buildings and structures.
Light reflection coefficients are used in calculating the reflected component in the design of natural and artificial lighting of buildings and structures (SP 52.13330.2011 and).
2 Normative references
In this standard, references are made to the following standards:
GOST 8.023-2014 State system for ensuring the uniformity of measurements. State verification scheme for measuring instruments of light quantities of continuous and pulsed radiation
GOST 8.332-2013 State system for ensuring the uniformity of measurements. Light measurements. The values of the relative spectral luminous efficiency of monochromatic radiation for daytime vision. General Provisions
GOST 26824-2010 Buildings and structures. Brightness measurement methods
SP 52.13330.2011 SNiP 23-05-95 * "Natural and artificial lighting"
Note - When using this standard, it is advisable to check the validity of the reference standards in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet or according to the annual information index "National Standards", which was published as of January 1 of the current year, and by the releases of the monthly information index "National Standards" for the current year. If the referenced standard to which an undated reference is given is replaced, it is recommended that the current version of that standard be used, subject to any changes made to that version. If the referenced standard to which the dated reference is given is replaced, then it is recommended to use the version of that standard with the above year of approval (acceptance). If, after the approval of this standard, a change is made to the referenced standard to which the dated reference is given, affecting the provision to which the reference is made, then that provision is recommended to be applied without taking into account that change. If the reference standard is canceled without replacement, then the provision in which the reference to it is given is recommended to be applied in the part that does not affect this reference.
When using this standard, it is advisable to check the validity of the reference set of rules in the Federal Information Fund of Technical Regulations and Standards.
3 Terms and definitions
In this standard, the terms according to GOST 26824 are used, as well as the following terms with the corresponding definitions, taking into account the existing international practice *:
________________
* See section Bibliography. - Note from the manufacturer of the database.
3.1 light reflection: A process in which visible radiation returns to a surface or medium without changing the frequency of its monochromatic components.
3.2 integral light reflectance , %:
The ratio of the reflected luminous flux to the incident luminous flux, calculated by the formula
where is the total luminous flux reflected from the sample surface;
- the luminous flux incident on the sample surface;
S- relative spectral power distribution of incident radiation of a standard light source;
is the total spectral reflectance of the sample surface;
V- relative spectral luminous efficiency of monochromatic radiation V with wavelength.
3.3 diffuse light reflectance , %:
The fraction of diffuse reflection of the luminous flux from the sample surface, calculated by the formula
where is the diffuse reflection of the light flux.
3.4 directional (specular) light reflection coefficient , %:
Reflection in accordance with the laws of specular reflection without diffusion, expressed as the ratio of the regular reflection of a part of the reflected luminous flux to the incident flux, calculated by the formula
where is the specular reflected luminous flux.
4 Requirements for measuring instruments
4.1 To measure the luminous flux, radiation converters should be used that have a permissible relative error limit of no more than 10%, taking into account the spectral correction error, defined as the deviation of the relative spectral sensitivity of the radiation measuring transducer from the relative spectral luminous efficiency of monochromatic radiation for daytime vision V according to GOST 8.332, errors in the calibration of the absolute sensitivity and the error caused by the nonlinearity of the light characteristic.
4.2 As a light source for measurements, a source of the type A.
The lamp supply voltage should be stabilized within 1/1000.
4.3 The photometer, the design of which must comply with the measurement schemes given in Sections 6-8, must meet the following requirements:
4.3.1 The optical system should ensure the parallelism of the light beam, the angle of divergence (convergence) not more than 1 °.
4.3.2 After the passage of the luminous flux after reflection from the sample of the material, the beams of light should fall on the photodetector with a deviation from the specified direction by no more than 2 °.
4.3.3 When determining the coefficient of directional reflection of light, the angle of incidence of the light beam is equal to the angle of reflection with an absolute error of ± 1 °.
4.3.4 The angle of incidence of the light beam on the photosensitive surface of the photodetector should be constant at all stages of measurements, unless an integrating sphere (Taylor ball) is used.
4.3.5 It is allowed when testing samples to use other devices that provide the results of measuring the reflection of light according to certified reference samples with a given error.
If a monochromator or spectrophotometer is used as a measuring instrument, the reflection coefficient is determined according to formulas (1), (2) or (3).
5 Sample requirements
5.1 The tests are carried out on samples of the materials used. The dimensions of the samples are set in accordance with the instructions for use of the used measuring instrument.
5.2 The surface of the samples should be flat.
5.3 The sampling procedure and the number of samples are established in the regulatory documents for a specific type of product.
6 Measurement of integral light reflectance
The measurement of the integral light reflectance is carried out using an integrating sphere, which is a hollow sphere with a coating of the inner surface having a high diffuse reflectance. There are holes in the sphere.
A schematic diagram of the measurement of the integral and diffuse light reflectance corresponding to * is shown in Figure 1.
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* See section Bibliography, hereinafter. - Note from the manufacturer of the database.
1 - sample; 2 - standard calibration port; 3 - port of incoming light; 4 - photometer; 5 - screen; d is the diameter of the hole for placing the measured sample (0.1 D); d- diameter of the calibration hole ( d= d); d- diameter of the hole for the incoming luminous flux (0.1 D); d- the diameter of the hole for the exit of the specularly reflected beam ( d= 0,02D); D- inner diameter of the sphere; - angle of incidence of the incoming beam (10 °)
Figure 1 - Schematic diagram of the measurement of integral and diffuse light reflectance
When measuring the integral reflectance, the hole for the exit of the specularly reflected beam with a diameter d missing or covered with a plug.
7 Measurement of diffuse reflectance of light
Measurement of the diffuse light reflectance is carried out according to the scheme shown in Figure 1.
In this case, the sphere must have a hole for the exit of a specularly reflected beam with a diameter d.
The standard size of the outlet aperture should be 0.02 D.
8 Measurement of directional (specular) light reflectance
The directional (specular) light reflectance of a surface is measured by illuminating the surface with a parallel or collimated light beam incident on the illuminated surface at an angle. A schematic diagram of the measurement of the specular reflection coefficient corresponding to it is shown in Figure 2.
9 Measurement methods
9.1 Absolute method
9.1.1 The essence of the method consists in determining the ratio of the current value of the photodetector when the light flux reflected from the test sample hits it to the value of the current when the light flux hits the photodetector.
9.1.2 Test procedure
9.1.2.1 The light beam from the light source is directed to the photodetector.
1 - collimating lens; 2 - a collector lens, the diaphragm of which is located at an angle; 3 - Light source; 4 - aperture of the collector of the photodetector; 5 - the surface of the measured sample; 6 - photodetector; - angle of incidence of the luminous flux; - the angle of the aperture holes
Figure 2 - Schematic diagram of the measurement of the specular reflection coefficient
9.1.2.2 Measure the current of the photodetector i.
9.1.2.3 Set the measurement plane.
9.1.2.4 The equipment is located in accordance with the optical scheme shown in Figure 1 or 2, depending on the measured value.
9.1.2.5 Place the test specimen in the measurement plane.
9.1.2.6 Measure the current of the photodetector i.
9.1.3 Processing of results.
9.1.3.1 The light reflectance is determined by the formula
where is the current strength of the photodetector with the sample under study, A.
is the current strength of the photodetector without a sample, A.
9.1.3.2 The relative measurement error is determined by the formula
- absolute error in measuring the current strength of the photodetector (absolute error of the photometer) without a sample.
9.2 Relative method
9.2.1 The essence of the method consists in determining the ratio of the current of the photodetector when the light flux reflected from the test sample hits it to the current of the photodetector when the light flux hits it, reflected from the sample having a certified value of the light reflectance, taking into account this coefficient ...
9.2.2 Test procedure
9.2.2.1 Specify the measurement plane.
9.2.2.2 The equipment is located in accordance with the optical scheme shown in Figure 1 or 2, depending on the measured value.
9.2.2.3 A specimen with a certified light reflectance (reference specimen) is placed in the measurement plane.
9.2.2.4 Measure the current of the photodetector i.
9.2.2.5 Place the test specimen in the measurement plane.
9.2.2.6 Measure the current of the photodetector i.
9.2.3 Expression of results
9.2.3.1 The light reflectance is determined by the formula
where is the certified light reflectance of the reference sample;
- current strength of the photodetector with the test sample, A;
is the current strength of the photodetector with the reference sample, A.
9.2.3.2 The relative measurement error is determined by the formula
where is the absolute error in determining the light reflectance;
- absolute error in measuring the current strength of the photodetector (absolute error of the photometer) with the test sample;
- absolute error in measuring the current strength of the photodetector (absolute error of the photometer) with a reference sample;
is the absolute error of the certified light reflectance of the reference sample.
Note - For the relative measurement error (9.1.3.2 and 9.2.3.2), it is allowed to take the specified error of the photometer.
Bibliography
Code of practice for design and construction "Natural lighting of residential and public buildings". |
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EN 12665: 2011 * | Light and lighting. Basic terms and criteria for specifying lighting requirements (EN 12665: 2011 Light and lighting - Basic terms and criteria for specifying lighting requirements) |
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Properties of the reflective surfaces of the luminaires. Methods of determination (EN 16268: 2013 Performance of reflecting surfaces for luminaries) |
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UDC 721: 535.241.46: 006.354 | OKS 91.040 | |
Key words: reflectance, illumination, natural lighting, artificial lighting |
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Electronic text of the document
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M .: Standartinform, 2016
