Line reflectance. Definition of constants of integration. Reflection coefficient of light by colored surfaces Reflection coefficient

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

Ф neg + Ф absorb + Ф 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 incident on it of any wavelength. All real bodies are not completely black. However, some of them in certain intervals of wavelengths are close in their properties to an absolutely black body. 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 an absolutely black body can be a small hole in a closed cavity. It is obvious that 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 a 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 radiation incident on it in the same spectral interval:

. (10)

The emissive and absorptive abilities 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 energy luminosity of an absolutely black body.

Thus, according to Kirchhoff's law, for all bodies the ratio of the spectral density of energy luminosity to the spectral absorption coefficient is equal to the spectral density of energy 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 energy luminosity of any body in any region of the spectrum is always less than the spectral density of the energy luminosity of an absolutely black body (at the same wavelength and temperature). In addition, it follows from this law that if a body at a certain temperature does not absorb electromagnetic waves in the range from l to l + d l, then it does not emit them in this range of lengths at a given temperature.

Analytical form of the function for a black body
was established by Planck on the basis of quantum ideas about the nature of radiation:

(12)

The emission spectrum of a black body has a characteristic maximum (Fig. 2), which shifts to the short-wavelength part with increasing temperature (Fig. 3). The position of the maximum spectral density of energy luminosity can be determined from expression (12) in the usual way, equating the first derivative to zero:

. (13)

Denoting , we get:

X – 5 ( – 1) = 0. (14)

Rice. 2 Fig. 3

The solution to this transcendental equation numerical method gives
X = 4, 965.

Hence,

, (15)

= = b 1 = 2.898 m K, (16)

Thus, the function reaches its maximum at a wavelength inversely proportional to the thermodynamic temperature of a blackbody ( Wien'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 temperature of the radiation. An approximate dependence of the color of the glow of the body on its temperature is given in Table. one.

Table 1

Wien's first law is also called displacement law , thus emphasizing that with increasing temperature, the maximum spectral density of energy 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 body temperature ( Wien's second law ):

The energy luminosity of a black body can be found from expression (12) by simple integration over the wavelength

(18)

where is the reduced Planck constant,

The energy luminosity of a black body is proportional to the fourth power of its thermodynamic temperature. This position is called Stefan-Boltzmann law , and the coefficient of proportionality s = 5.67×10 -8 – the Stefan-Boltzmann constant.

A black body is an idealization of real bodies. Real bodies emit radiation whose spectrum is not described by Planck's formula. Their energy 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 the coefficient is introduced into formula (19), showing 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 radiant energy and temperature of the electric furnace is based on seebeck effect, which consists in the occurrence 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 - a thermopillar. 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 series-connected thermocouples and the nature of the conductor materials.

The value of thermoEMF arising in the circuit due to the energy of the radiation incident on the thermal column junctions is measured by a millivoltmeter placed on the front panel of the measuring device. The scale of this device is graduated in millivolts.

The temperature of an absolutely black body (furnace) is measured using a thermoelectric thermometer, consisting of a single 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 room temperature to the instrument reading.

In this work, the thermoelectric power of a thermopillar 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, consequently, the energy luminosity (with equal time intervals between measurements and a constant radiator area):

where b- coefficient of proportionality.

Equating the right parts of equalities (19) and (22), we obtain:

s× T 4 =b xe,

where with is a constant value.

Simultaneously with the measurement of the thermoelectric power of the thermopillar, 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 temperature values ​​of a completely black body (furnace) and the corresponding values ​​of thermoelectric thermopillar thermoelectric power, determine the value of the coefficient proportional to
sti with, which should be the same in all experiments. Then build a dependency graph c \u003d f (T), which should have the form of a straight line parallel to the temperature axis.

Thus, in the laboratory work, the nature of the dependence of the energy luminosity of a completely black body on its temperature is established, i.e. the Stefan–Boltzmann law is verified.

When passing through the boundaries between 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). There is no wave transformation in this case.

Let us consider the energy relations 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 is the ratio of the amplitude of the transmitted and incident waves:

These coefficients can be determined knowing the acoustic characteristics of the media. When a wave is incident 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 is incident from medium 1 to medium 2, the transmission coefficient is denoted and defined as

. (3.4)

When a wave is incident 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 discontinuities in the material (inclusions of the medium with acoustic resistance different from the resistance of the controlled material).

It is precisely 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. The reflection from a discontinuity filled with gas approaches 100%, and for a discontinuity filled with slag, this coefficient is much lower.

When a wave is normally incident 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 intensity reflection and transmission coefficients are also used.

Intensity reflection coefficient is the ratio of the intensities of the reflected and incident waves. For normal wave incidence

, (3.7)

where is the reflection coefficient during the incidence from medium 1 to medium 2;

is the reflection coefficient when falling from medium 2 into medium 1.

Intensity Transmission Coefficient is 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 during the fall from medium 1 to medium 2;

is the transmission coefficient when falling from medium 2 to medium 1.

The direction of wave incidence does not affect the values ​​of the coefficients of reflection and intensity transmission. The law of conservation of energy through the coefficients of reflection and transmission is written as follows

When a wave is obliquely incident on the interface between media, it is possible to transform a wave of one type into another. The reflection and transmission processes in this case are characterized by several reflection and transmission coefficients, depending on the type of incident, reflected, and transmitted waves. The reflection coefficient in this form has the designation ( is an index indicating the type of the incident wave, is an index indicating the type of the reflected wave). Cases are possible. The transmission coefficient is denoted by ( is an index indicating the type of the incident wave, is an index indicating the type of the transmitted wave). There are cases , and .

The distribution of currents and voltages in a long line is determined not only by wave parameters that characterize the line's own properties and do not depend on the properties of circuit sections external to the line, but also by the line reflection coefficient, which depends on the degree of line matching with the load.

Complex reflection coefficient 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 constants of integration BUT 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 its 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 current and voltage at the end of the line:

where x" \u003d I - x - distance counted from the end of the line; p 2 \u003d p (x) |, \u003d / \u003d 0 neg (x) / 0 fell (x) x \u003d 1 \u003d 02 - Zj 2) / (U 2 + Zj 2) - reflection coefficient at the end of the line, the value of which is determined only by the ratio between the load resistance Z u \u003d U 2 / i 2 and line impedance Z B:

Like any complex number, the reflection coefficient of a line can be represented in exponential form:

Analyzing the expression (8.32), we establish that the modulus of the reflection coefficient

gradually increases with growth X and reaches the greatest 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 in 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 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 characteristic modes of its operation.

Traveling wave mode. Traveling wave mode the mode of operation of a homogeneous line is called, in which only the incident wave of voltage and current propagates in it, t.s. the amplitudes of the voltage and current of the reflected wave in all sections of the line are equal to zero. Obviously, in the mode of traveling waves, the reflection coefficient of the line p(lr) = 0. It follows from expression (8.32) that the reflection coefficient p(.r) can be equal to zero or in a line of infinite length (for 1=oo the incident wave cannot reach the end of the line and 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 \u003d 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 line load resistance be equal to the wave resistance 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 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 traveling wave mode in terms of 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 \u003d Let's move on from the complex operating values ​​​​of voltage and current to instantaneous:

As follows from expressions (8.41), in the mode of traveling will of the amplitude of 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 the voltage y (/) - r.g and current v | / (| - r.g in the traveling wave mode change 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:

A lossless line has a purely resistive impedance. (8.28), therefore, in the traveling wave mode, the phase shift between voltage and current in all sections of the lossless line is zero(y;

Instantaneous power consumed by a lossless line section located to the right of an arbitrary section X(see Fig. 8.1), is equal to the product of the instantaneous values ​​of voltage and current in the section X.

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 traveling wills, the energy is transferred 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 transmitted by the incident wave is consumed by the load.

Standing wave regime. If the load resistance of the line under consideration is not equal to the wave resistance, then only a part of the energy transmitted 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 as a reflected wave. If the line reflectance modulus |p(.r)| = 1, i.e. amplitudes of the reflected and incident waves are the same in all sections of the line, then a specific regime is established in the line, called standing wave regime. According to expression (8.34) the modulus of the reflection coefficient | p(lz)| = 1 only if the modulus of the reflection coefficient at the end of the line |p 2 | \u003d 1, and the line attenuation coefficient a \u003d 0. Analyzing expression (8.33), we can see that | p 2 | = 1 only in three cases: when the load resistance is either zero or infinity, or is purely reactive.

Hence, standing wave mode can only be established in the line without loss in the event of a short circuit or idling at the output, as well as, if the load resistance at the line output is purely reactive.

In the event of a short circuit at the output of the line, 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 into 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 zero, and passing from the complex effective values ​​of voltages and currents to instantaneous

we establish that in the event of a short circuit at the output of the line, the amplitudes of the voltage and current change along the line according to the periodic law

taking the 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).

Obviously, 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 equal to zero. Such points are called voltage (current) nodes.

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. Voltage amplitude distribution(a) and current(b) along the line in short circuit mode

Rice. 8.5. Distribution of instantaneous voltage values (a) and current (b) along the line in short circuit mode

The distribution of instantaneous values ​​of voltage and current along the line (Fig. 8.5) obeys a sinusoidal or cosine law, however, over time, the coordinates of points that have the same phase remain unchanged, i.e. voltage and current waves seem to "stand still". That is why this mode of operation of the line is called standing wave regime.

The coordinates of the voltage nodes are determined from the condition sin px /, = 0, from which

where to\u003d 0, 1,2, ..., and the coordinates of the antinodes of the voltage - from the condition cos p.g "(\u003d 0, whence

where P = 0, 1,2,...

In practice, the coordinates of nodes and antinodes are conveniently measured 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 \u003d kX / 2, x "„ \u003d (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 verify that voltage antinodes occur 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 the sections where the voltages of the incident and reflected waves are in antiphase and therefore subtracted. The instantaneous power consumed by an arbitrary section of the line changes with time according to the harmonic law

therefore, the active power consumed by this section of the line is zero.

Thus, in the standing will mode, energy is not transferred along the line, and only energy exchange between the electric and magnetic fields takes place in each section of the line.

Similarly, we find that in the idle mode (p2 \u003d 1), the distribution of voltage (current) amplitudes along the line without losses (Fig. 8.6)

has the same character as the distribution of current (voltage) amplitudes 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. Voltage amplitude distribution (a) and current (b) along the line at idle

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 output of the line | p 2 | = 1, and the values ​​of the argument р р2 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 voltage and current of the line:

where φ \u003d arctg (/? B / x "). From expression (8.47) it follows that the voltage and current amplitudes change along the line according to the periodic law:

where the coordinates of voltage nodes (current antinodes) x "k \u003d (2k + 1)7/4 + 1y where 1 = f7/(2tg); k= 0, 1, 2, 3,..., and the coordinates of the voltage antinodes (current nodes) X"" = PC/2 + 1, where P = 0, 1,2,3,...

The distribution of voltage and current amplitudes with a purely reactive load as a whole has the same character as in idle or short-circuit modes at the output (Fig. 8.7), and all nodes and all antinodes are shifted by 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 c/a from the end of the line (Fig. 8.7, a); with 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 represent 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 case, 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 a line with a capacitive(a) and inductive

In some cases, the line has a mixed-wave regime, which can be considered as a superposition of the regimes of traveling and standing waves. In the mixed wave regime, the energy transmitted by the incident wave to the end of the line is partially absorbed by the load and partially reflected from it, so 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 voltage and current amplitudes in the mixed wave mode (Fig. 8.8)

Rice. 8.8. Voltage amplitude distribution (a ) and current(b) along a line in mixed wave mode with a purely resistive load(R„ > RH)

has clearly defined highs and lows, repeating through X/2. However, the current and voltage amplitudes 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 ratios between the minimum and maximum values ​​of the voltage and current amplitudes 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 voltage or current amplitude is called traveling wave ratio(KBV)

KBV can vary from 0 to 1, and, the more K () Y, the closer the mode of operation of the line is to the mode of running wills.

Obviously, at the points of the line at which the amplitude of the voltage (current) reaches 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 are in antiphase. Hence,

Substituting expression (8.49) into relations (8.48) and taking into account that the ratio of the reflected wave voltage amplitude to the incident wave voltage amplitude is the modulus of the line reflection coefficient | р(лг)|, we establish the relationship between the coefficient of the traveling wave and the reflection coefficient:

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, so the coefficient of the traveling wave in all sections of the line has the same value: Kc>=

= (1-YUO+S).

In a lossy line, the modulus of the reflection coefficient changes along the line, reaching its maximum value at the reflection point (at X= /). 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 matching of the line with the load, the reciprocal of it is widely used - standing wave ratio(SWR):

In the traveling wave regime, K c = 1, and in the mode of standing waves K with-? oo.

GOST R 56709-2015

NATIONAL STANDARD OF THE RUSSIAN FEDERATION

BUILDINGS AND CONSTRUCTIONS

Methods for measuring the coefficients of light reflection by the 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 federal state budget institution"Research Institute of Building Physics Russian Academy architecture and construction sciences" ("NIISF RAASN") with the participation of the Limited Liability Company "CERERA-EXPERT" (LLC "CERERA-EXPERT")

2 INTRODUCED by the Technical Committee for Standardization TC 465 "Construction"

3 APPROVED AND PUT INTO EFFECT by Order of the Federal Agency for Technical Regulation and Metrology dated 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 about 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 - in the monthly information index "National Standards". In case of revision (replacement) or cancellation of this standard, a corresponding notice will be published in the next issue of the monthly information index "National Standards". Relevant information, notification and texts are also placed in information system general use - 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 standard establishes methods for measuring the integral, diffuse and specular light reflectance of materials used for interior decoration and facades of buildings and structures.

Light reflection coefficients are used in calculations of the reflected component in the design of natural and artificial lighting of buildings and structures (SP 52.13330.2011 and).

2 Normative references

References are made in this standard to the following standards:

GOST 8.023-2014 State system 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. Values ​​of the relative spectral luminous efficiency of monochromatic radiation for daytime vision. General provisions

GOST 26824-2010 Buildings and structures. Methods for measuring brightness

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 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 on issues of the monthly information index "National Standards" for the current year. If an undated referenced reference standard has been replaced, it is recommended that the current version of that standard be used, taking into account all this version changes. If the reference standard to which the dated reference is given is replaced, then it is recommended to use the version of this standard with the year of approval (acceptance) indicated above. If, after the adoption of this standard, a change is made to the referenced standard to which a dated reference is given, affecting the provision to which the reference is given, then this provision is recommended to be applied without taking into account this 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 operation of the reference set of rules in the Federal Information Fund of Technical Regulations and Standards.

3 Terms and definitions

This standard uses the terms according to GOST 26824, as well as the following terms with appropriate definitions, taking into account existing international practice *:
________________
* See section Bibliography. - Database manufacturer's note.

3.1 light reflection: The process by which visible radiation returns to surfaces or media without changing the frequency of its monochromatic components.

3.2 integral light reflection coefficient , %: 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;

is the light flux incident on the surface of the sample;

S- relative spectral power distribution of the incident radiation of a standard light source;

is the total spectral reflection coefficient of the sample surface;

V- relative spectral luminous efficiency of monochromatic radiation V with a wavelength.

3.3 diffuse light reflectance , %: Fraction of diffuse reflection of the light flux from the surface of the sample, calculated by the formula

where is the diffuse reflection of the light flux.

3.4 coefficient of directional (specular) reflection of light , %: Reflection according to the laws of specular reflection without diffusion, expressed as the ratio of the regular reflection of a part of the reflected light flux to the incident flux, calculated by the formula

where is the specular reflected light flux.

4 Requirements for measuring instruments

4.1 To measure the luminous flux, radiation converters should be used that have a limit of permissible relative error of not more than 10%, taking into account the spectral correction error, defined as the deviation of the relative spectral sensitivity of the measuring radiation converter from the relative spectral luminous efficiency of monochromatic radiation for daytime vision V according to GOST 8.332, absolute sensitivity calibration errors and errors caused by the non-linearity of the light characteristic.

4.2 As a light source for measurements, use a source of type A.

The lamp supply voltage must 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 must ensure the parallelism of the light beam, the angle of divergence (convergence) is not more than 1°.

4.3.2 After the passage of the light flux after reflection from the material sample, the rays of light should fall on the photodetector with a deviation from the given 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 equal to the angle reflections with an absolute error of ±1°.

4.3.4 The angle of incidence of the light beam on the light-sensitive surface of the photodetector must be constant at all stages of measurements, unless an integrating sphere (Taylor ball) is used.

4.3.5 When testing samples, it is allowed to use other instruments that provide measurement results of light reflection on certified reference samples with a given error.

If a monochromator or spectrophotometer is used as a measuring instrument, the determination of the reflection coefficient is carried out according to formulas (1), (2) or (3).

5 Sample requirements

5.1 Tests are carried out on samples of the materials used. The dimensions of the samples are set in accordance with the operating instructions for the measuring instrument used.

5.2 The surface of the specimens must be flat.

5.3 The selection procedure and the number of samples are established in the regulatory documents for products of a particular type.

6 Measuring the integrated light reflectance

The measurement of the integral light reflection coefficient is carried out using an integrating sphere, which is a hollow ball with a coating of the inner surface, which has a large diffuse reflection coefficient. The sphere has holes.

A schematic diagram of the measurement of the integral and diffuse light reflectance, corresponding to *, is shown in Figure 1.
________________
* See section Bibliography, here and below. - Database manufacturer's note.

1 - sample; 2 - standard calibration port; 3 - incoming light port; 4 - photometer; 5 - screen; d- diameter of the hole for placing the measured sample (0.1 D); d- diameter of the calibration hole ( d= d); d- hole diameter for the incoming light flux (0.1 D); d- 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 the integral and diffuse light reflectance

When measuring the integral reflection coefficient, the hole for the exit of the specularly reflected beam with a diameter d missing or covered by a plug.

7 Diffuse light reflectance measurement

The measurement of the diffuse reflectance of light is carried out according to the scheme shown in Figure 1.

In this case, the sphere must have a hole for the output of a specularly reflected beam with a diameter d.

Standard outlet aperture size 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 beam of light incident on the illuminated surface at an angle . Schematic diagram of the measurement of the specular reflection coefficient, corresponding to , is shown in Figure 2.

9 Measurement methods

9.1 Absolute method

9.1.1 The essence of the method is to determine the ratio of the value of the current strength of the photodetector when a light flux reflected from the test sample hits it, to the value of the current strength when the light flux directly 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 aperture of which is located at an angle; 3 - Light source; 4 - aperture of the photodetector collector; 5 - surface of the measured sample; 6 - photodetector; - angle of incidence of the luminous flux; - aperture angle

Figure 2 - Schematic diagram of the measurement of the specular reflection coefficient

9.1.2.2 Measure the photodetector current i.

9.1.2.3 Set the measurement plane.

9.1.2.4 The equipment is placed in accordance with the optical scheme shown in Figure 1 or 2, depending on the measured indicator.

9.1.2.5 Place the test specimen in the measurement plane.

9.1.2.6 Measure the photodetector current i.

9.1.3 Handling results.

9.1.3.1 The light reflectance is determined by the formula

where is the current strength of the photodetector with the test sample, A.

- 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 is to determine the ratio of the current strength of the photodetector when it hits the light flux reflected from the test sample to the current strength of the photodetector when it hits the light flux reflected from the sample having a certified value of the light reflection coefficient, taking into account this coefficient .

9.2.2 Test procedure

9.2.2.1 Set the measurement plane.

9.2.2.2 The equipment is placed in accordance with the optical scheme shown in Figure 1 or 2, depending on the measured indicator.

9.2.2.3 A sample with a certified light reflectance (reference sample) is placed in the measurement plane.

9.2.2.4 Measure the photodetector current i.

9.2.2.5 Place the specimen under test in the measurement plane.

9.2.2.6 Measure the photodetector current i.

9.2.3 Handling 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;

- current strength of the photodetector with a 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 reflection coefficient;

- absolute error in measuring the current strength of the photodetector (absolute error of the photometer) with the sample under study;

- absolute error in measuring the current strength of the photodetector (absolute error of the photometer) with a reference sample;

- absolute error of the certified light reflection coefficient 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 rules for design and construction "Natural lighting of residential and public buildings".
	EN 12665:2011*	Light and illumination. EN 12665:2011 Light and lighting - Basic terms and criteria for specifying lighting requirements
________________ * Access to international and foreign documents mentioned in the text can be obtained by contacting the User Support Service. - Database manufacturer's note.
		Properties of reflective surfaces of luminaires. Methods of determination (EN 16268:2013 Performance of reflecting surfaces for luminaries)

UDC 721:535.241.46:006.354	OKS 91.040
Keywords: reflection coefficient, illumination, natural light, artificial light

Electronic text of the document
prepared by Kodeks JSC and verified against:
official publication
M.: Standartinform, 2016

Reflection coefficient is a dimensionless physical quantity that characterizes the ability of a body to reflect radiation incident on it. Greek is used as a letter $\backslash rho$ or latin $R$ .

Definitions

Quantitatively, the reflection coefficient is equal to the ratio of the radiation flux reflected by the body to the flux that fell on the body:

$\backslash rho\; =\; \backslash frac(\backslash Phi)(\backslash Phi\_0).$

The sum of the reflection coefficient and the coefficients of absorption, transmission and scattering is equal to one. This statement follows from the law of conservation of energy.

In those cases where the spectrum of the incident radiation is so narrow that it can be considered monochromatic, one speaks of monochromatic reflection coefficient. If the spectrum of radiation incident on the body is wide, then the corresponding reflection coefficient is sometimes called integral.

In the general case, the value of the reflection coefficient of a body depends both on the properties of the body itself and on the angle of incidence, spectral composition, and polarization of the radiation. Due to the dependence of the reflection coefficient of the surface of the body on the wavelength of the light incident on it, the body is visually perceived as painted in one color or another.

Specular reflection coefficient $\backslash rho\_r~(R\_r)$

It characterizes the ability of bodies to mirror the radiation incident on them. Quantitatively determined by the ratio of the specularly reflected radiation flux $\backslash Phi\_r$ to the falling stream:

$\backslash rho\_r=\backslash frac(\backslash Phi\_r)(\backslash Phi\_0).$

Specular (directional) reflection occurs when radiation is incident on a surface whose irregularities are much smaller than the radiation wavelength.

Diffuse reflectance $\backslash rho\_d~(R\_d)$

Characterizes the ability of bodies to diffusely reflect the radiation incident on them. Quantitatively determined by the ratio of the diffusely reflected radiation flux $\backslash Phi\_d$ to the falling stream:

$\backslash rho\_d=\backslash frac(\backslash Phi\_d)(\backslash Phi\_0).$

If both specular and diffuse reflections occur simultaneously, then the reflection coefficient $\backslash rho$ is the sum of the coefficients of the mirror image $\backslash rho\_r$ and diffuse $\backslash rho\_d$ reflections:

$\backslash rho=\backslash rho\_r+\backslash rho\_d.$

see also

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Notes

An excerpt characterizing the reflectance (optics)

- Oh, Natasha! - she said.
- Did you see it? Did you see? What did you see? cried Natasha, holding up the mirror.
Sonya didn’t see anything, she just wanted to blink her eyes and get up when she heard Natasha’s voice saying “by all means” ... She didn’t want to deceive either Dunyasha or Natasha, and it was hard to sit. She herself did not know how and why a cry escaped her when she covered her eyes with her hand.
- Did you see him? Natasha asked, grabbing her hand.
- Yes. Wait ... I ... saw him, ”Sonya said involuntarily, still not knowing who Natasha meant by his word: him - Nikolai or him - Andrei.
“But why shouldn’t I tell you what I saw? Because others see it! And who can convict me of what I saw or did not see? flashed through Sonya's head.
“Yes, I saw him,” she said.
- How? How? Is it worth it or is it lying?
- No, I saw ... That was nothing, suddenly I see that he is lying.
- Andrey lies? He is sick? - Natasha asked with frightened fixed eyes looking at her friend.
- No, on the contrary - on the contrary, a cheerful face, and he turned to me - and at the moment she spoke, it seemed to her that she saw what she was saying.
- Well, then, Sonya? ...
- Here I did not consider something blue and red ...
– Sonya! when will he return? When I see him! My God, how I fear for him and for myself, and for everything I am afraid ... - Natasha spoke, and without answering a word to Sonya's consolations, she lay down in bed and long after the candle was put out, with her eyes open, lay motionless on bed and looked at the frosty, moonlight through the frozen windows.

Soon after Christmas, Nikolai announced to his mother his love for Sonya and his firm decision to marry her. The countess, who had long noticed what was happening between Sonya and Nikolai, and was expecting this explanation, silently listened to his words and told her son that he could marry whomever he wanted; but that neither she nor his father would give him blessings for such a marriage. For the first time, Nikolai felt that his mother was unhappy with him, that despite all her love for him, she would not give in to him. She, coldly and without looking at her son, sent for her husband; and when he arrived, the countess wanted to briefly and coldly tell him what was the matter in the presence of Nikolai, but she could not stand it: she burst into tears of annoyance and left the room. The old count began to hesitantly admonish Nicholas and ask him to abandon his intention. Nicholas replied that he could not change his word, and his father, sighing and obviously embarrassed, very soon interrupted his speech and went to the countess. In all clashes with his son, the count did not leave the consciousness of his guilt before him for the disorder of affairs, and therefore he could not be angry with his son for refusing to marry a rich bride and for choosing Sonya without a dowry - he only on this occasion more vividly recalled that, if things had not been upset, it would be impossible for Nicholas to wish for a better wife than Sonya; and that only he, with his Mitenka and his irresistible habits, is to blame for the disorder of affairs.