If anyone has not read the article, I strongly recommend that you read it, because the topic of today’s article will have something in common with the previous one. For everyone else, I will repeat the summary once again. There are three types of cameras: compact, mirrorless and DSLR. Compact ones are the simplest, and mirror ones are the most advanced. The practical conclusion of the article was that for more or less serious photography, you should opt for mirrorless and DSLR cameras.

Today we will talk about the device of the camera. As in any business, you need to understand the principle of operation of your tool for confident management. It is not necessary to know the device thoroughly, but you need to understand the main components and operating principle. This will allow you to look at the camera from a different perspective - not as a black box with an input signal in the form of light and an output in the form of a finished image, but as a device in which you understand and understand where the light goes next and how the final result is obtained. We won’t touch on compact cameras, but rather talk about DSLR and mirrorless cameras.

SLR camera design

Globally, a camera consists of two parts: a camera (also called the body) and a lens. The carcass looks like this:

Carcass - front view

Carcass - top view

And this is what the camera looks like complete with a lens:

Now let's look at the schematic image of the camera. The diagram will show the structure of the camera “in cross-section” from the same angle as in the last image. The numbers on the diagram indicate the main components that we will consider.

After adjusting all the settings, framing and focusing, the photographer presses the shutter button. At the same time, the mirror rises and the stream of light falls on the main element of the camera - the matrix.

As you can see, the mirror rises and shutter 1 opens. The shutter in DSLRs is mechanical and determines the time during which light will enter matrix 2. This time is called shutter speed. It is also called the matrix exposure time. Key shutter characteristics: shutter lag and shutter speed. Shutter lag determines how quickly the shutter curtains open after you press the shutter button - the lower the lag, the more likely it is that that car rushing past you that you're trying to capture will be in focus, not blurred, and framed the way you did when using the viewfinder. For DSLRs and mirrorless cameras, the shutter lag is small and is measured in ms (milliseconds). The shutter speed determines the minimum amount of time the shutter will be open - i.e. minimum shutter speed. On budget cameras and mid-level cameras, the minimum shutter speed is 1/4000 s, on expensive ones (mostly full-frame) - 1/8000 s. When the mirror is raised, light does not enter either the focusing system or the pentaprism through the focusing screen, but directly onto the sensor through the open shutter. When you take a picture with a SLR camera and look through the viewfinder all the time, then after pressing the shutter you will temporarily see black spot, not an image. This time is determined by the shutter speed. If you set the shutter speed to 5 seconds, for example, then after pressing the shutter button you will see a black spot for 5 seconds. After the matrix is ​​exposed, the mirror returns to its original position and light again enters the viewfinder. IT IS IMPORTANT! As you can see, there are two main elements that regulate the flow of light entering the sensor. This is aperture 2 (see previous diagram), which determines the amount of light transmitted, and the shutter, which regulates shutter speed - the time it takes for light to hit the matrix. These concepts are at the heart of photography. Their variations achieve different effects and it is important to understand their physical meaning.

Camera matrix 2 is a microcircuit with photosensitive elements (photodiodes) that react to light. In front of the matrix there is a light filter, which is responsible for obtaining a color image. Two important characteristics of the matrix are its size and signal-to-noise ratio. The higher both are, the better. We will talk more about photomatrices in a separate article, because... this is a very broad topic.

From the matrix, the image goes to the ADC (analog-to-digital converter), from there to the processor, processed (or not processed if shooting in RAW) and saved to a memory card.

More to important details DSLRs can be classified as aperture repeaters. The fact is that focusing is done with the aperture fully open (as far as possible is determined by the design of the lens). By setting a closed aperture in the settings, the photographer does not see changes in the viewfinder. In particular, the depth of field remains constant. To see what the output frame will be like, you can press the button, the aperture will close to the set value and you will see the changes before pressing the shutter button. An aperture repeater is installed on most DSLRs, but few people use it: beginners often don’t know about it or don’t understand its purpose, while experienced photographers know approximately what the depth of field will be in certain conditions and it’s easier for them to take a test shot and, if necessary, change the settings .

Mirrorless camera design

Let's immediately look at the diagram and discuss in detail.

Mirrorless cameras are much simpler than DSLRs and are essentially their simplified version. They don't have a mirror and complex system phase focusing, and a different type of viewfinder is installed.

The light flux enters through the lens onto matrix 1. Naturally, the light passes through the diaphragm in the lens. It is not indicated on the diagram, but I think, by analogy with DSLRs, you guessed where it is located, because the lenses of DSLRs and mirrorless cameras are practically the same in design (except in size, bayonet mount and number of lenses). Moreover, most lenses from DSLRs can be installed on mirrorless cameras via adapters. Mirrorless cameras do not have a shutter (more precisely, it is electronic), so the shutter speed is adjusted by the time during which the matrix is ​​turned on (receives photons). As for the matrix size, it corresponds to Micro 4/3 or APS-C format. The second is used more often and fully corresponds to matrices built into DSLRs from the budget to the advanced amateur segment. Now full-frame mirrorless cameras have begun to appear. I think that in the future the number of FF (Full Frame) mirrorless cameras will increase.

In the diagram, number 2 indicates the processor, which receives the information received by the matrix.

Under the number 3 is a screen on which the image is displayed in real time (Live View mode). Unlike DSLRs, this is not difficult to do in mirrorless cameras, because the light flow is not blocked by the mirror, but flows freely onto the matrix.

In general, everything looks just great - complex structural mechanical elements (mirror, focusing sensors, focusing screen, pentaprism, shutter) have been removed. This made production much easier and cheaper, reduced the size and weight of the devices, but also created a lot of other problems. I hope you remember them from the section on mirrorless cameras in the article about. If not, then now we will discuss them, simultaneously examining what technical features caused by these shortcomings.

The first major problem is the viewfinder. Since the light hits the matrix directly and is not reflected anywhere, we cannot see the image directly. We see only what gets onto the matrix, then is incomprehensibly converted in the processor and displayed on an incomprehensible screen. Those. There are many errors in the system. Moreover, each element has its own delays and we do not see the image right away, which is unpleasant when shooting dynamic scenes (due to the constantly improving characteristics of processors, viewfinder screens and matrices, this is not so critical, but it still happens). The image is displayed on the electronic viewfinder, which has a high resolution, but which still cannot be compared with the resolution of the eye. Electronic viewfinders tend to become blind in bright light due to limited brightness and contrast. But it is more than likely that in the future this problem will be overcome and a pure image passed through a series of mirrors will go into oblivion just like “correct film photography.”

The second problem arose due to the lack of phase detection autofocus sensors. Instead, a contrast method is used, which determines by contour what should be in focus and what should not. In this case, the objective lenses move a certain distance, the contrast of the scene is determined, the lenses move again and again the contrast is determined. And so on until maximum contrast is reached and the camera focuses. This takes too much time and is less accurate than the phase system. But at the same time, contrast autofocus is a software function and does not take up additional space. Nowadays they have already learned to integrate phase sensors into mirrorless matrices, creating hybrid autofocus. In terms of speed, it is comparable to the autofocus system of DSLRs, but so far it is installed only in selected expensive models. I think this problem will also be solved in the future.

The third problem is low autonomy due to the fact that it is stuffed with electronics that are constantly working. If the photographer is working with the camera, then all this time the light enters the matrix, is constantly processed by the processor and displayed on the screen or electronic viewfinder with high speed updates - the photographer must see what is happening in real time, and not in recordings. By the way, the latter (I’m talking about the viewfinder) also consumes energy, and not a little, because its resolution is high and brightness and contrast should be at the same level. I note that with increasing pixel density, i.e. when their size decreases with the same power consumption, brightness and contrast inevitably decrease. Therefore, to power high-quality screens with high resolution a lot of energy is wasted. Compared to DSLRs, the number of frames that can be taken on a single battery charge is several times less. For now, this problem is critical, because it will not be possible to significantly reduce energy consumption, and we cannot count on a breakthrough in batteries. At least this problem has existed for a long time in the market of laptops, tablets and smartphones and its solution has not been successful.

The fourth issue presents both an advantage and a disadvantage. We're talking about camera ergonomics. Due to the removal of “unnecessary elements” of mirror origin, the dimensions have decreased. But they are trying to position mirrorless cameras as a replacement for DSLRs, and the size of the matrices confirms this. Accordingly, the lenses used are not the most small size. A small mirrorless camera, similar to a digital compact, simply disappears from view when using a telephoto lens (a lens with a long focal length that brings objects very close). Also, many controls are hidden in the menu. In DSLRs they are placed on the body in the form of buttons. And it’s simply more pleasant to work with a device that fits well in your hand, doesn’t tend to slip out, and in which you can quickly change settings by touch without thinking. But camera size is a double-edged sword. On the one hand, a large size has the advantages described above, and on the other hand, a small camera fits into any pocket, you can take it with you more often and people pay less attention to it.

As for the fifth problem, it is related to optics. There are currently many mounts (types of lens mounts for cameras). There are an order of magnitude fewer lenses made for them than for the mounts of the main DSLR systems. The problem is solved by installing adapters, with which you can use the vast majority of DSLR lenses on mirrorless cameras. Sorry for the pun)

Compact camera design

As for compacts, they have a lot of limitations, the main one of which is the small size of the matrix. This does not allow you to get a picture with low noise, high dynamic range, high-quality blurring of the background and imposes a lot of other restrictions. Next up is the autofocus system. If DSLRs and mirrorless cameras use phase and contrast types of autofocus, which are classified as a passive type of focusing, since they do not emit anything, then compacts use active autofocus. The camera emits a pulse infrared light, which is reflected from the object and hits the camera. The travel time of this pulse determines the distance to the object. This system is very slow and does not work over significant distances.

Compacts use non-replaceable low-quality optics. A wide range of accessories is not available for them, as for their older brothers. Sighting occurs in Live View mode on the display or through the viewfinder. The latter is ordinary glass, not very good quality, is not connected to the camera's optical system, resulting in incorrect framing. This is especially noticeable when shooting nearby objects. The operating time of compacts on a single charge is short, the body is small and its ergonomics are much worse than those of mirrorless cameras. The number of available settings is limited and they are hidden deep in the menu.

If we talk about the design of compacts, then it is simple and is a simplified mirrorless camera. It has a smaller and worse matrix, a different type of autofocus, no normal viewfinder, no ability to replace lenses, low battery life and ill-conceived ergonomics.

Conclusion

We briefly looked at the design of cameras various types. I think now you have a general idea about internal structure cameras This topic is very broad, but to understand and control the processes that occur when shooting with certain cameras at different settings and with different optics, I think the above information will be enough. In the future, we will still talk about individual essential elements: matrix, autofocus systems and lenses. For now, let's leave it at that.

1. Luminous flux

Luminous flux is the power of radiant energy, assessed by the light sensation it produces. Radiation energy is determined by the number of quanta that are emitted by the emitter into space. Radiation energy (radiant energy) is measured in joules. The amount of energy emitted per unit time is called radiation flux or radiant flux. The radiation flux is measured in watts. The luminous flux is designated Fe.

where: Qе - radiation energy.

The radiation flux is characterized by the distribution of energy in time and space.

In most cases, when talking about the distribution of radiation flux over time, they do not take into account the quantum nature of the occurrence of radiation, but understand this as a function that gives a change in time of instantaneous values ​​of the radiation flux Ф(t). This is acceptable because the number of photons emitted by the source per unit time is very large.

According to the spectral distribution of the radiation flux, sources are divided into three classes: with line, stripe and continuous spectra. The radiation flux of a source with a line spectrum consists of monochromatic fluxes of individual lines:

where: Фλ - monochromatic radiation flux; Fe - radiation flux.

For sources with a striped spectrum, radiation occurs within fairly wide areas of the spectrum - bands separated from one another by dark intervals. To characterize the spectral distribution of the radiation flux with continuous and striped spectra, a quantity called spectral flux density

where: λ - wavelength.

The spectral radiation flux density is a characteristic of the distribution of the radiant flux over the spectrum and is equal to the ratio of the elementary flux ΔФeλ corresponding to an infinitesimal area to the width of this area:

Spectral radiation flux density is measured in watts per nanometer.

In lighting engineering, where the main receiver of radiation is the human eye, to evaluate effective action radiation flux, the concept of luminous flux is introduced. Luminous flux is the flux of radiation, assessed by its effect on the eye, the relative spectral sensitivity of which is determined by the average spectral efficiency curve approved by the CIE.

In lighting technology, the following definition of luminous flux is used: luminous flux is the power of light energy. The unit of luminous flux is lumen (lm). 1 lm corresponds to the luminous flux emitted in a unit solid angle by a point isotropic source with a luminous intensity of 1 candela.

Table 1. Typical light quantities light sources:

Types of lamps	Electric Energy, W	Luminous flux, lm	Luminous output lm/w
	100 W	1360 lm	13.6 lm/W
Fluorescent Lamp	58 W	5400 lm	93 lm/W
Sodium lamp high pressure	100 W	10000 lm	100 lm/W
Sodium lamp low pressure	180 W	33000 lm	183 lm/W
High pressure mercury lamp	1000 W	58000 lm	58 lm/W
Metal halide lamp	2000 W	190000 lm	95 lm/W

The light flux Ф falling on a body is distributed into three components: reflected by the body Фρ, absorbed by Фα and transmitted Фτ. When using the following coefficients: reflection ρ = Фρ /Ф; absorption α =Фα/Ф; transmission τ = Фτ / Ф.

Table 2. Light characteristics of some materials and surfaces

Materials or surfaces	Odds			Character of reflection and transmission
	reflections ρ	absorption α	transmission τ
Chalk	0,85	0,15	-	Diffuse
Silicate enamel	0,8	0,2	-	Diffuse
Mirror aluminum	0,85	0,15	-	Directed
Glass mirror	0,8	0,2	-	Directed
Frosted glass	0,1	0,5	0,4	Directional-scattered
Organic milk glass	0,22	0,15	0,63	Directional-scattered
Opal silicate glass	0,3	0,1	0,6	Diffuse
Silicate milk glass	0,45	0,15	0,4	Diffuse

2. Light power

The distribution of radiation from a real source in the surrounding space is not uniform. Therefore, the luminous flux will not be an exhaustive characteristic of the source if the distribution of radiation in different directions of the surrounding space is not simultaneously determined.

To characterize the distribution of light flux, the concept of spatial density of light flux in different directions of the surrounding space is used. The spatial density of the luminous flux, determined by the ratio of the luminous flux to the solid angle with the vertex at the point where the source is located, within which this flux is evenly distributed, is called luminous intensity:

where: F - luminous flux; ω - solid angle.

The unit of luminous intensity is the candela. 1 cd.

This is the luminous intensity emitted in a perpendicular direction by a blackbody surface element with an area of ​​1:600000 m2 at the solidification temperature of platinum.
The unit of luminous intensity is the candela, cd is one of the basic quantities in the SI system and corresponds to a luminous flux of 1 lm, uniformly distributed within a solid angle of 1 steradian (avg). A solid angle is a part of space enclosed inside a conical surface. Solid angleω is measured by the ratio of the area it cuts out from a sphere of arbitrary radius to the square of the latter.

3. Illumination

Illuminance is the amount of light or luminous flux incident on a unit surface area. It is designated by the letter E and measured in lux (lx).

The unit of illumination lux, lux has the dimension lumen per square meter(lm/m2).

Illumination can be defined as the density of luminous flux on an illuminated surface:

Illumination does not depend on the direction of propagation of the light flux onto the surface.

Here are some generally accepted illumination indicators:

Summer, day under a cloudless sky - 100,000 lux

Street lighting- 5-30 lux

Full moon on a clear night - 0.25 lux

4. The relationship between luminous intensity (I) and illuminance (E).

Inverse square law

Illumination at a certain point on a surface perpendicular to the direction of propagation of light is defined as the ratio of luminous intensity to the square of the distance from this point to the light source. If we take this distance as d, then this relationship can be expressed by the following formula:

For example: if a light source emits light with an intensity of 1200 cd in a direction perpendicular to the surface at a distance of 3 meters from this surface, then the illuminance (Ep) at the point where the light reaches the surface will be 1200/32 = 133 lux. If the surface is at a distance of 6 m from the light source, the illumination will be 1200/62 = 33 lux. This relationship is called "inverse square law".

Illumination at a certain point on a surface not perpendicular to the direction of light propagation is equal to the luminous intensity in the direction of the measurement point, divided by the square of the distance between the light source and the point on the plane multiplied by the cosine of the angle γ (γ is the angle formed by the direction of incidence of the light and the perpendicular to this plane).

Hence:

This is the law of cosine (Figure 1).

Rice. 1. To the law of cosine

To calculate horizontal illumination, it is advisable to change the last formula by replacing the distance d between the light source and the measurement point with the height h from the light source to the surface.

In Figure 2:

Then:

We get:

Using this formula, the horizontal illumination at the measurement point is calculated.

Rice. 2. Horizontal illumination

6. Vertical illumination

Illumination of the same point P in a vertical plane oriented towards the light source can be represented as a function of the height (h) of the light source and the angle of incidence (γ) of luminous intensity (I) (Figure 3).

luminosity:

For surfaces of finite dimensions:

Luminosity is the density of the luminous flux emitted by a luminous surface. The unit of luminosity is the lumen per square meter of luminous surface, which corresponds to a surface of 1 m2 that uniformly emits a luminous flux of 1 lm. In the case of general radiation, the concept of energetic luminosity of the radiating body (Me) is introduced.

The unit of energetic luminosity is W/m2.

Luminosity in this case can be expressed through the spectral energy luminosity density of the emitting body Meλ(λ)

For a comparative assessment, we reduce the energy luminosities to the luminosities of some surfaces:

Sun surface - Me=6 107 W/m2;

Incandescent lamp filament - Me=2 105 W/m2;

The surface of the sun at the zenith is M=3.1 109 lm/m2;

Fluorescent lamp bulb - M=22 103 lm/m2.

This is the intensity of light emitted per unit surface area in a specific direction. The unit of measurement for brightness is candela per square meter (cd/m2).

The surface itself can emit light, like the surface of a lamp, or reflect light that comes from another source, like the surface of a road.

Surfaces with different properties reflections under the same illumination will have different degrees of brightness.

The brightness emitted by a surface dA at an angle Ф to the projection of this surface is equal to the ratio of the intensity of light emitted in a given direction to the projection radiating surface(Fig. 4).

Rice. 4. Brightness

Both the luminous intensity and the projection of the emitting surface do not depend on distance. Therefore, brightness is also independent of distance.

Some practical examples:

Sun surface brightness - 2000000000 cd/m2

Brightness fluorescent lamps- from 5000 to 15000 cd/m2

Full moon surface brightness - 2500 cd/m2

Artificial road lighting - 30 lux 2 cd/m2

All professional electricians are familiar with the concept of calculating room illumination. This operation must be carried out for every room in the house. It is definitely the foundation of lighting in general.

In our article today, we will try to understand a number of issues related to this procedure. Amateur electricians do not understand much, so we explain everything to the smallest detail.

Calculation of lighting in both residential and production premises must be produced with high precision. The state of human health and a comfortable pastime in this room directly depend on these indicators.

If the room has insufficient or excessive illumination, this factor will play a role in psychological state human, and will also bring some consequences for the visual organ. To avoid such troubles, this process must be planned.

We determine the calculation of illumination for a living space

For this method, it is necessary to perform a number of preliminary actions, for example, calculate the number of lighting fixtures per room, and let’s start with this:

• For this we need a formula, where

N is the number of lighting fixtures;

E - indicator of lighting values ​​in a horizontal position, measured in Lux;

S is the area of ​​the room in which the calculation is carried out;

Kr is a reserve coefficient characterizing the excess level of illumination. It is provided in case of failure of a certain number of lamps;

U is a coefficient that determines the possibility of using the device;

n is the number of light bulbs that the lighting fixture contains;

Fl is the light emission of one light bulb, Lm.

• Next we need to find the room index using the formula:

To make accurate calculations, you need to measure the height of the lamp and the height of the proposed zone for which the illumination is being calculated, the values ​​a and b are the lengths of the walls, which also need to be determined;

Auxiliary methods for determining room illumination

In addition to the basic mathematical method of determining the lighting level for the required area, there are more simplified options, which are also regularly used at home.

Calculation by power density . This tactic is quite simple, since all the reference data is available. Among the shortcomings, the only thing that can be highlighted is that the calculation is obtained with a large excess. To determine the specific power value, you need to multiply the number of lamps by the power of each of them separately, then divide the resulting expression by the area of ​​the room. In this way, the required lamp power value is obtained, from which their number can be easily determined.

Calculation using a prototype. This method is quite simple, since all the data is available in tables typical for typical premises. This option is convenient for living conditions. There is no point in using calculations of a more professional type for everyday life.

Spot illumination calculation. Using this calculation, it is possible to obtain a value for each individual point in the room. However, this type of calculation requires lengthy preparation: it is necessary to have a room plan with markings of lamps, according to which you should select a point that serves as a calculation point. This option is complex and is used for difficult conditions or with design features of wall or ceiling surfaces.

Important! In order to simplify your task and find the exact value of illumination, you need to collect all the data and use a calculator that determines the level of lighting in the rooms.

Factors influencing workplace illumination?

For each separate room There are certain requirements that determine a number of factors that must be taken into account. At this stage, we will consider how to calculate illumination for working area or office.

Each type of activity should be equipped with an optimal level of luminous flux, and it does not matter whether you are working at a computer or at a production machine. Before ensuring sufficient comfort at your place of work, you must take into account the following factors:

• sufficiency of light and its uniformity;
• desired brightness;
• glare or glare effect is not allowed;
• correct contrast and color range of light;
• no light pulsation.

In addition to the listed factors, due attention must be paid to quantitative and qualitative criteria. Let's turn to qualitative criteria.

1. Direct fading is a set of objects or surfaces that brightly reflect light, while causing discomfort to human vision. This disadvantage can be eliminated by increasing the height of the lamps, installing diffusers on the light source and reducing the power of each bulb.
2. Reflected fading occurs when individual surfaces in a room have an increased reflectance. Due to this factor, a person can see a mirror or bright spot of light, and this quite interferes and irritates the vision. To eliminate this factor, it is necessary to properly organize the lighting, following the calculations using the formula.
3. High contrast. This factor is also not favorable. For example, if the surface of the work area has a contrast similar to the luminous flux, in such cases some details will be indistinguishable to the human eye.

Note! For the purpose of good vision and distinction of objects in the workplace, it is necessary that the surface of the illuminated area and the luminous flux have a different contrast.

1. Shadow. Required complete absence falling shadows, for example, from parts of the human body and objects installed in the work area. It is believed that such shadows are harmful because they reduce vision. In addition, they distort the contrast of details important for vision. To eliminate this criterion, it is important to place the lighting on that side of the surface so that even with the maximum tilt of a person, shadows do not form.
2. Light saturation. It is important here not to confuse the level of illumination of the working area and the light saturation of the entire room. These two characteristics are in this case are considered compatible. To avoid under-saturation, it is necessary to install unfocused lighting, as well as decorate walls and ceiling surface light coatings.

What is lighting pulsation and how to determine its level?

Doesn't exist today lighting fixture, which would produce a uniform luminous flux, and this does not indicate any defect in the device. Such a phenomenon, if present, cannot be noticed, but this does not reduce its danger to human vision.

The pulsation coefficient represents a certain change that occurs in the time of emission of the light flux that falls on the surface. To calculate this value, you should subtract the minimum value for the same time from the maximum illumination value for a certain period of time, and multiply the resulting value by 100%. The resulting number is expressed as a percentage.

Attention! There are a number of specific standards that are regulated by law regarding lighting pulsation. There are specific restrictions for each individual room.

In places where essential work tasks and operations are performed, this value should not exceed 20%. In public and administrative buildings, a pulsation value not exceeding 5% is provided.

Is it possible to measure the pulsation of light?

As it turned out, it is impossible to visually determine the state of pulsation of the light flux; therefore, it is necessary to use special equipment. Such devices include an illumination meter, a device for determining the brightness of light, and a device that indicates the exact value of the pulsation coefficient. Thanks to such devices, the following is achieved:

• exact value of room illumination;
• the brightness of devices transmitting artificial light is calculated;
• the pulsation of the light flux wave is determined;
• The pulsation of monitors of various electronic devices is clarified.

Based on the calculation results, the following values ​​are identified: the pulsation coefficient of LED lamps is 100%; less pulsation is produced by incandescent lamps and “housekeepers” - 25%. When choosing expensive lamps for residential lighting, you cannot guarantee that the pulsation coefficient will be harmless.

Standards for illumination of premises according to SNIP

The current document, which to this day regulates the pulsation coefficient and illumination indicators for premises, is the set of rules (SP), legalized in 2015. The latest version of SNIP 05/23/95 clarifies all criteria relating to electrical efficiency and safety.

Let's look at the table of standards from SNIP that residential premises must have.

Using table values, you can easily determine the required values ​​for each room in a residential building.

How to calculate the illumination rate in Lumens: not the traditional method

According to statistics, this method is considered the most accurate compared to others given, but it is used only in exceptional cases. In order to use this determination tactic, we need to take the total area of ​​the measured room, multiply this value by the normalized illumination indicator for 1 square meter. m, as a result we obtain the strength of light radiation necessary for the entire room as a whole.

Attention! All regulatory values ​​regarding lighting standards for residential premises can be found in SNIP documents.

>>Illuminance

• Remember how you felt when you entered a dark room. It becomes somehow uneasy, because you can’t see anything around... But as soon as you turn on the flashlight, nearby objects become clearly visible. Those that are located somewhere further can be barely distinguished by their contours. In such cases, they say that objects are illuminated differently. Let's find out what illumination is and what it depends on.

1. Determine the illumination

A luminous flux spreads from any light source. The greater the light flux that falls on the surface of a particular body, the better it is visible.

• A physical quantity numerically equal to the luminous flux incident on a unit of illuminated surface is called illumination.

Illumination is indicated by the symbol E and is determined by the formula:

where F is the luminous flux; S is the surface area on which the luminous flux falls.

In SI, the unit of illumination is taken to be lux (lx) (from Latin Iux - light).

One lux is the illumination of such a surface, per square meter of which a luminous flux equal to one lumen falls:

Here are some surface values ​​(near the ground).

Illumination E:

Sunlight at noon (at mid-latitudes) - 100,000 lux;
sunlight in an open place on a cloudy day - 1000 lux;
sun rays in bright room(near the window) - 100 lux;
on the street at artificial lighting- up to 4 lux;
from the full moon - 0.2 lux;
from the starry sky on a moonless night - 0.0003 lux.

2. Find out what illumination depends on

You've probably all seen spy movies. Imagine: some hero, in the light of a weak flashlight, carefully looks through documents in search of the necessary “secret data”. In general, to read without straining your eyes, you need illumination of at least 30 lux (Fig. 3.9), and this is a lot. And how does our hero achieve such illumination?

First, he holds the flashlight as close as possible to the document he is viewing. This means that illumination depends on the distance from the illuminated object.

Secondly, it positions the flashlight perpendicular to the surface of the document, which means that the illumination depends on the angle at which the light hits the surface.

Rice. 3.10. If the distance to the light source increases, the area of ​​the illuminated surface increases

And in the end, for better lighting he can simply take a more powerful flashlight, since it is obvious that as the source of light increases, the illumination increases.

Let's find out how illumination changes when the distance from a point light source to the illuminated surface increases. Let, for example, a luminous flux from a point source fall on a screen located at a certain distance from the source. If you double the distance, you will notice that the same luminous flux will illuminate an area 4 times larger. Since, the illumination in this case will decrease by 4 times. If you increase the distance by 3 times, the illumination will decrease by 9 - 3 2 times. That is, illumination is inversely proportional to the square of the distance from a point light source to the surface (Fig. 3 10).

If a beam of light falls perpendicular to the surface, then the luminous flux is distributed over a minimal area. If the angle of incidence of light increases, the area on which the luminous flux falls increases, so the illumination decreases (Fig. 3.11). We have already said that if the intensity of the light source increases, the illumination increases. It has been experimentally established that illumination is directly proportional to the light intensity of the source.

(Illumination decreases if there are particles of dust, fog, smoke in the air, since they reflect and scatter a certain part of the light energy.)

If the surface is located perpendicular to the direction of propagation of light from a point source and the light propagates in clean air, then the illumination can be determined by the formula:

where I is the luminous intensity of the source, R is the distance from the light source to the surface.

Rice. 3.11 In the case of increasing the angle of incidence of parallel rays on the surface (a 1< а 2 < а 3) освещенность этой поверхности уменьшается, поскольку падающий световой поток распределя­ется по все большей площади поверхности

3. Learning to solve problems

The table is illuminated by a lamp located at a height of 1.2 m directly above the table. Determine the illumination of the table directly under the lamp if the total luminous flux of the lamp is 750 lm. Consider a lamp as a point source of light.

• Let's sum it up

A physical quantity numerically equal to the luminous flux F incident on a unit of illuminated surface S is called illumination. In SI, the lux (lx) is taken as the unit of illumination.

The illumination of the surface E depends: a) on the distance R to the illuminated surface b) on the angle at which the light falls on the surface (the smaller the angle of incidence, the greater the illumination); c) on the luminous intensity I of the source (E - I); d) transparency of the medium in which light propagates, passing from the source to the surface.

• Control questions

1. What is called illumination? In what units is it measured?
2. Is it possible to read without straining your eyes in a bright room? outdoors under artificial light? under the full moon?

3. How can you increase the illumination of a certain surface?

4. The distance from the point light source to the surface was increased by 2 times. How did the illumination of the surface change?

5. Does the illumination of a surface depend on the intensity of the light source that illuminates this surface? If it depends, then how?

• Exercises

1. Why is the illumination of horizontal surfaces at noon greater than in the morning and evening?

2. It is known that illumination from several sources is equal to the sum of illumination from each of these sources separately. Give examples of how this rule is applied in practice.

3. After studying the topic “Lighting,” seventh-graders decided to increase the illumination of their workplace:

Petya replaced the light bulb in his desk lamp with a higher power bulb;
- Natasha put another one table lamp;
- Anton raised the chandelier that hung above his table higher;
- Yuri positioned the table lamp in such a way that the light began to fall almost perpendicular to the table.

Which students did the right thing? Justify your answer.

4. On a clear noon, the illumination of the Earth's surface by direct sunlight is 100,000 lux. Determine the luminous flux incident on an area of ​​100 cm2.

5. Determine the illumination from a 60 W electric light bulb located at a distance of 2 m. Is this illumination sufficient for reading a book?

6. Two light bulbs placed side by side illuminate the screen. The distance from the light bulbs to the screen is I m. One light bulb was turned off. How much closer do you need to move the screen so that its illumination does not change?

• Experimental task

To measure the intensity of light, instruments called photometers are used. Make a simple analogue of a photometer. To do this, take White list(screen) and place it on it grease stain(for example, oil). Fix the sheet vertically and illuminate it from both sides with different light sources (S 1, S 2) (see figure). (The light from the sources should fall perpendicular to the surface of the sheet.) Slowly move one of the sources until the spot becomes almost invisible. This will happen when the illumination of the spot on one and the other side is the same. That is, E 1 = E 2.

Because the . Measure the distance from the first source to the screen (R 1) and the distance from the second source to the screen (R 2).

Compare how many times the luminous intensity of the first source differs from the luminous intensity of the second source: .

• Physics and technology in Ukraine

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Physics. 7th grade: Textbook / F. Ya. Bozhinova, N. M. Kiryukhin, E. A. Kiryukhina. - X.: Publishing house "Ranok", 2007. - 192 p.: ill.

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