It is difficult to meet a person who does not understand the measures of length, area, volume, and weight. It is not difficult to calculate time or determine temperature. But if you ask someone about photometric quantities, then in most cases you cannot expect a clear answer. Meanwhile, we live in constant contact with lighting, natural or artificial. This means that we must learn to evaluate it in some way.

Of course, such an assessment is always made by everyone, but most often - purely at the level of subjective perception: is there enough light or not. However, such a “gradation” is precisely subjective and can produce significant errors. The consequences of such incorrect assessments cannot be underestimated - both insufficient lighting and its excess negatively affect both a person’s visual organs and his psycho-emotional state.

Meanwhile, there is a special value - illumination, the value of which is regulated by legislative acts in the field of construction and sanitation. That is, illumination is precisely the quality criterion that allows you to correctly evaluate the organization of a room lighting system. In this article we will talk about this parameter and other photometric quantities associated with it, and see how this can be used in a practical application.

Due to ingrained habit, many continue to believe that the assessment of room illumination can be done in energy units - watts. This misconception is easily explained - we are left with this persistent stereotype as a legacy from the times of complete dominance of incandescent lamps.

Incandescent lamps were produced with different power consumption - 15, 25, 40, 60, 75, 100, 150 and more watts. And every owner of a house or apartment knew from his own experience that for normal lighting in the living room, for example, he must screw three 60-watt bulbs into a chandelier, a “forty” will be enough for a table lamp, a hundred-watt one for the kitchen, etc.

By the way, a clear legacy of this is still the practice used by lamp manufacturers - to indicate on their packaging, in addition to power consumption, luminous efficiency expressed in the equivalent power of old incandescent lamps.

So let's remember the first thing - neither the luminous flux emitted by a lamp nor the surface illumination resulting from it is measured in watts. The watts indicated on the body of the device are the amount of electricity consumed by the lamp, which, through certain physical transformations, is converted into visible light.

Some people of the older generation are generally confident that the light output lighting fixture measured in candles. By the way, this is not so far from the truth, and why will become clear below. But again, this is not illumination at all.

So it makes sense to consider the main photometric quantities in order, from the light source to the illuminated surface. Let’s make a reservation right away – this topic is quite difficult for an unprepared person to understand. Therefore, we will try to simplify the presentation as much as possible and will not overload it with cumbersome formulas. So that there is simply a general understanding of the issue.

Light flow

Light, as is known, has a wave nature. In a certain wavelength range electromagnetic radiation is perceived by the human visual organs, that is, it becomes visible. The approximate boundaries of this range are from 400÷450 nm (red part of the spectrum) to 630÷650 (violet region).

Electromagnetic waves are a carrier of energy - it is the energy of the Sun that provides life on Earth. But let's digress from astronomical categories and return to ordinary light sources.

So, since a source emits light, this means radiation and transfer of a certain energy. The amount of this radiant energy (We) transferred per unit time is called radiant flux (Fe). And it is measured in watts.

However, we are talking about lighting, that is, the perception of color by human vision. And estimating the amount of energy “by eye” means immediately introducing a large error. For example, two sources with equal radiation power, but with different colors glows will also be perceived by the eye differently.

To unify this parameter, a special physical quantity was introduced - luminous flux (F). This is also an indicator of the power of the radiant flux, but only that part of it that is perceived by the average healthy human eye.

Luminous flux can also be measured in watts (this is rather an energy indicator), or in lumens (light indicator). In practice, lumens are usually used.

For the exact value of one lumen, radiation from the central, green part of the visible spectrum, with a length of 555 nm, was taken as a standard.

So, it is accepted that a radiant flux with a wavelength of 555 nm and a value of 1 watt corresponds to 683 lumens. Why such a strange coefficient? It’s just that the final approval of this unit in the SI system took place in 1979, and the first experiments in photometry with the introduction of the indicator luminous flux began to be produced long before that. At that time, when electric lighting did not yet exist, and an ordinary candle served as a more or less stable, “reference” light source. And the current ratio of energy watt and light lumen was recalculated over time and passed down to the present day.

Let us remind you once again that the watts mentioned above, which can also be used to measure the luminous flux, have nothing to do with those indicated on the lamp packaging. It shows the consumption of the lamp, that is, the amount of energy that it will “take” from the network. We should be more concerned about its energetic light output - how much visible radiant energy it will “give out”. So, when choosing a lamp, it would be much more correct to pay attention not to ephemeral comparative analogies in watts, but to the clearly indicated value of the luminous flux in lumens.

Luminous output

This is a very interesting quantity in practical terms, since it essentially characterizes the efficiency of the light source. It is important to choose a lamp not based on its electrical power consumption, but on how this power is used when converted into light energy.

So, the luminous output value shows how much luminous flux is produced by the lamp when converting one watt of expended energy. It is clear that it is measured in lumens per watt (lm/W).

The conversion of one type of energy into another is carried out in different ways. For example, in conventional incandescent lamps the resistive principle is used - the glow is caused by a red-hot coil with high electrical resistance. It is clear that this is accompanied by huge heat losses. More efficient are modern lighting devices based on the principles of glow of semiconductor matrices when current is passed or specially selected gas mixtures are ionized. Here, significantly less energy is wasted on unnecessary heating.

It was already mentioned above that the peak of normal perception of light by the human eye occurs at a wavelength of 555 nm. And in ideal conditions, with full transformation electrical energy in a monochromatic light flux of the specified wavelength, that is, with absolutely no losses, it is theoretically possible to achieve a light output of 683 lm/W. This is called an ideal light source, which, alas, does not exist in nature.

The table below shows comparative characteristics for the most commonly used lamps in everyday life - incandescent, fluorescent and LED. It is clearly visible how more economical the use of modern light sources becomes, that is, how the luminous efficiency increases.

(The values ​​in the table are approximate. In any category of lamps there may be deviations in one direction or another - this depends on the quality of the particular model. But the table presents the general picture quite clearly).

Luminous flux, Lm	Incandescent lamps		Fluorescent lamps		LED bulbs
	Consumed Power, W	Luminous output lm/W	Consumed Power, W	Luminous output lm/W	Consumed Power, W	Luminous output lm/W
250	20	12.5	5÷7	41.7	2÷3	100
400	40	10	10÷13	36.4	4÷5	88.9
700	60	11.7	15÷16	45.2	6÷10	87.5
900	75	12	18÷20	47.4	10÷12	81.8
1200	100	12	25÷30	43.6	12÷15	88.9
1800	150	12	40÷50	40	18÷20	94.7
2500	200	12.5	60÷80	38.5	25÷30	90.9

The specific luminous efficiency value is not always, but is still indicated by some lamp manufacturers on their packaging. This may be the inscription “light output” or “Lighting effect”. If not, then it’s easy to determine it yourself by dividing the nameplate luminous flux by the specified power consumption.

It is quite obvious that of all the lamps used in domestic conditions, the best luminous efficiency indicators are LED devices– for them this figure reaches 100 lm/W, and may even be slightly higher. But progress does not stand still, and the developers announce an imminent release serial production lamps with a luminous efficiency of about 200 lm/W. But the ideal source is still oh so far away...

By the way, scientists were able to estimate the luminous efficiency of the Sun, and it is not so high: approximately 93 lm/W.

About the luminous efficiency of light sources various types This is also explained in the video below:

Video: What is luminous efficiency, and what is the practical application of this parameter?

The power of light

In physics there is the concept of a point source of light - it propagates radiation exactly the same in all directions. In practice, if this happens, it is extremely rare, and even then - with some simplification of concepts. In fact, the light flux in different directions is uneven. And in order to estimate, let’s say, its spatial density, they operate with the magnitude of the light intensity. And to understand what it is, you will also have to remember the concept of a solid angle.

Let's start with geometry. So, a solid angle is a part of space that unites all rays emanating from one point and intersecting a certain surface (it is called a subtending surface). In photometry, of course, this is an illuminated surface. This angle is measured in special quantities - steradians (sr), and is usually indicated in formulas by the symbol Ω .

The magnitude of the solid angle is the ratio of the area of ​​the subtending surface to the radius of the sphere.

Ω = S/R²

That is, if we take, for example, a sphere with a radius of one meter, then a solid angle of one steradian will “cut” a spot on its surface with an area of ​​one square meter.

Why know this? The fact is that the concept of luminous intensity is directly related to the solid angle. Specifically, a luminous flux of one lumen, propagating in a space limited by a solid angle of one steradian, has a luminous intensity of one candela. Mathematically, this relationship looks like this:

I = Ф/ Ω

And if we talk about the energy intensity of light equal to one candela, then this is 1/683 W/sr.

By the way, the candela is one of the seven basic quantities of the SI system.

Candela literally means candle in Latin. This is exactly that “relic of the past” that was already mentioned above, but it very clearly shows the entire interconnection of quantities.

Let's explain in the figure:

So, there is a point source of light - a candle. Its burning wick emits light with an intensity of one candela (item 1).

In a space limited by a solid angle equal to one steradian (item 2), a luminous flux (item 3) equal to one lumen will propagate. At a certain distance from the source (radius of the sphere - position 4), this flow illuminates the surface of a certain area (position 5). Looking ahead, we will immediately say that if the area is equal to one square meter, then under such conditions in this “light spot” an illumination equal to one lux (lx) is provided.

If we return to the candle as a reference light source, then it is easy to calculate its total luminous flux. A complete sphere has a solid angle of 4π, that is, with slight rounding, it is equal to 12.56 steradians. This means that a candle emitting light of one candela in all directions produces a total luminous flux of 12.56 lumens.

It is interesting that not so long ago the emissivity of light sources was assessed “in candles”. For example, they said that you need a “light bulb for sixty candles.” Sellers and buyers understood each other perfectly - a 60 W incandescent light bulb was purchased, although, in fact, these values ​​​​are in no way related to each other in this case, from a physics point of view, are not related. And what’s funny is that it was close to the truth.

Let's see - 60 candles of 12.56 lumens will give a total of 753.6 lumens. Let's look at the table above - an incandescent lamp with a consumption of 60 watts has a luminous flux of approximately 700 lumens. Very close!

But, we repeat, a correct assessment of light sources should still be carried out in lumens.

Light brightness

Another parameter worth considering is the brightness of the light source. The fact is that there is practically no need to deal with point sources. That is, most sources have some kind of specific radiating surface. And with an equal luminous flux, but a different area of ​​light emission, it will be perceived differently by vision.

That is, in essence, brightness is the strength of light emitted from a certain unit area of ​​the visible surface of a light source.

It is clear that the unit of brightness will be candela per square meter.

This is an important value, since the organs of vision, when looking at a light source, react, rather, not to the intensity of light as such, but rather to brightness. When its value is large (over 160 thousand candelas per square meter), the light can cause eye irritation, pain, and tearfulness. That's why lighting manufacturers produce lamps with frosted bulbs. With virtually no loss of luminous flux, the radiation does not come specifically from an incandescent filament or LED with their small areas, but from a much larger surface area of ​​the bulb. This glow is much safer for the retina of the eye and is perceived much more comfortably by vision.

Surface illumination

Finally, we got to the lighting. This value can be considered the most applied, since it is the illumination of a particular area that is assessed general work lighting fixtures.

Figuratively speaking, illumination (E) is the surface density of the luminous flux (F) distributed over a particular area (S). If we approach it with some simplification, then this can be expressed by the following formula:

As we saw above, one lumen of luminous flux on an area of ​​one square meter creates an illumination equal to one lux (lx).

Illumination depends on a number of factors, even if you do not take into account the own characteristics of the light source.

• Firstly, the further the source is located from the illuminated surface, the larger the area of ​​the “light spot” (remember the solid angle cone). That is, the luminous flux is distributed over larger area. Moreover, as we remember, this dependence is quadratic. That is, when the distance changes by half, the illumination will decrease by four times, by three times by nine times, etc.

If we consider a point source, we can apply Kepler’s formula:

We will not repeat the meaning of the quantities included in the formula - they are given above.

• Secondly, the Kepler formula shown above is valid only for a surface perpendicular to the direction of the light flux. In reality, of course, this does not happen often. That is, in the case when the illuminated plane is located at some angle α to the direction of the flow, corrections have to be made for this:

E = (I / r²) × cos α.

Remember - when you need to illuminate a surface as brightly as possible, you point the flashlight perpendicular to it. But if you place it at an angle, the illumination will drop sharply, since the light seems to be “smeared” across the surface.

• Thirdly, the illumination of a particular area also depends on its, so to speak, surroundings. The fact is that most surfaces do not absorb all the light that hits them, but largely reflect it. And thus they themselves become original sources of light.

Let's remember what was said in the section about the brightness of the glow. Yes, indeed, the brightness of such illuminated areas is not particularly high. But the radiation comes from a decent area, and as a result a very significant luminous flux is created.

And the brightness of such an illuminated surface depends both on its illumination and on its diffuse reflectivity, which has a separate name - albedo. The higher the albedo, the brighter the glow. And since it’s brighter, the “secondary” color flow is more studied.

Some illustrative examples reflected light. A sheet of white paper with illumination of only 50 lux will have a brightness of 15 cd/m². The glow of the full moon (and this, as we know, is sunlight reflected from its surface) is characterized by a brightness of 2500 cd/m². And the surface of pure white snow on a sunny day reaches a brightness of up to 3000 cd/m². Quite a lot!

This phenomenon is very widely used in lighting and design rooms. Entire model lines of lamps are produced that are specially designed to be directed towards walls or ceilings, that is, it is the illuminated areas that are included in the work of general lighting of the room. The same effect is used when creating multi-tiered ceiling structures with LED strip lighting.

It is easy to guess that the illumination of the room will depend on the chosen style of its decoration. The same light bulb, say, in a white room will provide much greater illumination than in one painted in dark colors.

Since the final expected result of the operation of lighting devices is the creation of comfortable and healthy lighting indicators in the room, it is the value of surface illumination that is subject to regulation. Legislative acts (SNiP and SanPiN) indicate what illumination should be achieved in various rooms, depending on their purpose.

Thus, the current SNiP 23-05-95 in its updated version (Code of Rules SP 52.13330.2011) specifies the following standard illumination indicators for residential buildings:

Type (purpose) of the premises	Illumination standards in accordance with current SNiP, luxury
Living rooms	150
Children's rooms	200
Office, workshop or library	300
Cabinet for precision drawing work	500
Kitchen	150
Shower room, separate or combined bathroom, bathroom	50
Sauna, locker room, swimming pool	100
Entrance hall, corridor, hall	50
Entrance lobby	30
Stairs and landings	20
Wardrobe	75
Sports (gym) room	150
Billiard room	300
Storage room for strollers or bicycles	30
Technical rooms – boiler room, pump room, electrical control room, etc.	20
Auxiliary passages, including in attics and basements	20
Area at the main entrance to the house (porch)	6
Area at the emergency or technical entrance	4
Pedestrian path at the entrance to the house for 4 meters	4

In this case, the assessment of illumination should be carried out on a horizontal plane at floor height. For stairs - both at floor height and on transition platforms and steps.

To assess the level of illumination, they are used special devices– lux meters. They consist of a photodetector with a spherical sensor surface, and a converter unit with an analog (arrow) or digital indication of readings.

It is clear that a lux meter is a highly specialized, expensive device that is used by specialists, and which is absolutely not required to have at home. But understanding the basic photometric quantities will not hurt any owner of a house or apartment.

For what? - many may ask. Yes, at least in order to be able to independently plan the use of certain light sources in order to achieve required illumination. After all, the health and general mood of all family members directly depends on it.

The practical position of this knowledge will be discussed in the next section of the publication.

Colorful temperature

To finish the conversation about the main characteristics of light sources, it is necessary to dwell on their color temperature.

With completely equal indicators of the emitted luminous flux, one light bulb can give a warm yellowish color, another - a neutral white, and a third, for example, can glow with a cold shade of blue. How to distinguish them by this parameter? A special color temperature scale has been developed for this purpose.

Let's make a reservation right away - there is no connection between the air temperature in the room or the heating temperature of the light source itself. The glow of a physical body heated to high temperatures is simply taken as a standard.

Any body, if its temperature is above absolute zero, is itself a source infrared radiation. As the temperature rises, the wavelength of this radiation changes, and at a certain moment it reaches the visible part of the spectrum.

Probably everyone has observed this - when heated, a metal rod first turns red, then begins to glow with a bright red light; you can heat it, as they say, “white-hot.” And when performing electric welding work, when the arc temperature reaches very high levels, the melting metal can acquire a blue tint.

It is this gradation that forms the basis of the color temperature scale. It is indicated in Kelvin - and on the scale you can see what kind of glow the lamp will emit.

This color temperature is usually indicated in the lamp labeling. Sometimes it is accompanied by a text explanation, or even a miniature scale showing in which region of the visible spectrum the lamp will glow.

The choice of lamps based on their color temperature depends on what kind of environment you plan to maintain in the room. Of course, a subjective factor will also play a significant role here - that is, the preferences of the owners. And there are no ready-made “recipes” for this. But the table below provides a recommended overview of lamps based on their glow. Perhaps this will help someone when choosing.

Colorful temperature	Visual perception	Possible definitions of the created atmosphere	Typical Applications
2700 K	Warm light	Open, warm, friendly, cozy, relaxing	Living rooms, hotel lobbies, small boutiques, restaurants, cafes
3000 K	White light	Intimate, friendly, conducive to communication	Living rooms, libraries, shops, offices
3700 K	Neutral light	Friendly, conducive to communication, giving a feeling of security, increasing attentiveness	Museums and exhibition halls, bookstores, offices
4100 K	Cold light	Focus-promoting, clean, clear, productive	Training premises, design bureaus, offices, Bolgitsy, large stores, train stations
5000 - 6500 K	Cold daylight	Disturbing, overly bright, emphasizing colors, sterile, tiring over time	Museums, jewelry stores, some offices in medical institutions

Carrying out independent calculations.

As promised, this section of the publication will discuss the algorithm for calculating illumination. More precisely, to be more correct, the calculation has just the opposite direction. That is, we already know the normal illumination value. And calculations should lead us to the result of how many lamps and with what luminous flux will be required to provide it.

General formula for calculations

So, let's start with the formula that will serve as the basis for our calculations.

Fl = (En × Sp × k × q) / (Nc × n × η)

Fl- this is the luminous flux of the lamp that needs to be installed in the lamp. That is, this is the very value that is the purpose of the calculations.

Yong- standard illumination of surfaces, depending on the type of room. It corresponds to the parameters established by SNiP and given above in the table. That is, we start from the standard value.

Sp- area of ​​the illuminated surface. Usually the area of ​​the room appears here if the general lighting is calculated. But if the goal is to calculate the illumination of a local area (for example, working area), then it is the area of ​​this zone that is substituted.

k- correction factor, which is often called the safety factor. Its introduction takes into account several circumstances affecting the luminous efficiency of lamps. Firstly, many lamps begin to waste their emitting potential over time, or, simply put, to dim. Secondly, the emissivity can be influenced by some external factors- this is the dustiness of the room or, say, a high concentration of steam, which prevents the free propagation of light rays.

Since we are talking about residential premises, where dense steam should not exist, and dust is removed by regular cleaning, then the second group of factors can be discounted. And for the gradual loss of emissivity, the coefficient for different types lamps can be adopted as follows:

Fluorescent lamps (gas discharge): 1.2;

Conventional incandescent and halogen lamps: 1.1;

LED lamps: 1.0.

q- a coefficient that takes into account the uneven glow of certain types of lamps. It is taken equal to:

For incandescent and gas discharge lamps mercury lamps: 1.2;

For compact fluorescent incandescent lamps and LED light sources: 1.1.

Let's move on to the denominator of the fraction.

Nc- the number of lighting fixtures planned for installation in the room or in a separate zone for which the calculation is being carried out.

n- the number of horns in the lamp planned for installation.

It is probably clear that the product of the last two values ​​shows how many lamps are planned for installation. For example, one five-arm chandelier is installed. Then Nc=1, and n=5. Or you plan to illuminate the room with two devices, each with three light bulbs: Nc=2, a n=3, But if the lighting is provided by one device with one lamp, both of these quantities will be equal to one.

η - luminous flux utilization factor. This correction value takes into account many factors relating to both the characteristics of the room and the specifics of the lighting fixtures planned for installation.

Since it is precisely this coefficient that remains an unknown value, calculations should begin with it.

Finding the luminous flux utilization factor

This value can be called a tabular empirical value. It depends on the area of ​​the room, and on the location of the lamp, and on the main direction of the light flux, and on the finishing of the flux surfaces, walls and floors.

First of all, to enter the table you will have to define the so-called premises index. It takes into account the dimensions of the room, moreover, precisely in the ratio of length and width, since in square room and in an elongated rectangular shape the light flux will still spread differently. And secondly, it takes into account the height of the lamp above the illuminated surface. As we remember, according to SNiP requirements, illumination is assessed on a horizontal plane at floor level.

Important - sometimes the height of the ceiling in a room is confused with the installation height of the lamp. But this is still not the same thing! For example, a lighting fixture can be mounted on a wall (sconce), installed on a stand or placed on a table or bedside table (floor lamp or table lamp), or suspended from the flow at a certain distance from the ceiling surface (chandelier).

The formula probably won't tell you anything. It’s better to suggest using an online calculator to determine this room index.

In the previous article we answered the question “how much light” is needed for general lighting. Now let's talk about how best to illuminate individual dark corners of the room: how many light bulbs and which ones will be needed to illuminate certain areas. Agree that the night light above the baby’s bed and the sconce above the sofa require different brightness.

• 1 of 1

On the picture:

Small and bold: even a miniature light bulb can provide the level of illumination you need.

Light level is the surface density of the luminous flux incident on an area of ​​a given size. It is measured in lux (lx).

Analyzing the table

Select the premises you are interested in (column) and the type of activity (row). Find the recommended light level (listed in the first column).

Levels illuminated ness, lux	common room	Office, children's room	Bedroom	Kitchen, dining room	Entrance hall, corridor	Bathroom, toilet
1000	sewing	-	-	-	-	-
500	picture lighting	drawing	-	-	-	-
300	-	sitting reading, writing	-	food processing	cosmetics technical procedures	-
200	reading; food	Board games	cosmetics logical procedures, reading while lying down	eating, serving	toilet by the mirror	shaving, washing
150	ironing	selection of books	-	washing dishes	reception of guests	washing, washing
100	-	outdoor games	nursing	placing and retrieving products	-	-
75	cleaning	cleaning	cleaning	cleaning	dressing; cleaning	cleaning
50	-	dressing, sports	dressing, sports	-	-	-
10	TV	for orientation at night	for orientation at night	for orientation at night	for orientation at night	for orientation at night

We measure the length of the lamp suspension. The expected power of the lamps depends on the length of the suspension: the closer the lamp is to the illuminated surface, the dimmer the lamps can be. Save energy - lower the lamp as low as possible!

In the photo: Beat Light lamp from the Tom Dixon factory, design by Dixon Tom.

Measuring the distance to the surface

Suppose you received some number - the value of the illumination level. So, to watch TV, the illumination level should be 10 lux, to read a book on the sofa, 200 lux is required, and when working at a desk or while cooking in the kitchen - about 300 lux.

Let's take the last figure and, using this example, calculate the required light intensity, and therefore the power of the lamps. To do this, we need to find out one more value: this is the estimated distance from the light bulb to the surface that needs to be illuminated. After all, if your chandelier hangs on a long suspension, you will need less lamp power than in the case of a lampshade directly on the ceiling. Let's say, in our case, the lamp in the kitchen will be located above work surface at a height of 45 cm

How to choose a lampshade?

How to choose a lampshade? The shape and material of the lampshade affects how light spreads in space. An opaque lampshade (cone or hemisphere) directs the flow of light only downwards. It is suitable for illuminating a table or any item that you would like to highlight by placing it in a "circle of light". Colored lampshades are suitable for the same purposes. They are not suitable for general lighting, but they add colorful spots to the interior. In order to illuminate the room with even and bright light, choose either a light textile lampshade of any shape or a glass shade.

Determining the intensity of light

We know the desired level of illumination and the distance from the light bulb to the surface. It remains to substitute the value into the formula
I = E * r²

Where
I - luminous intensity in candelas (cd);
E - illumination level (lx);
r is the distance to the light source (m).

As a result, we simply multiply the square of the distance (45 cm) by the illumination level (300 lux) and get I = 300*0.45*0.45. We obtain the desired value of luminous intensity (I) - in our case it is equal to 60.75 cd.

• 1 of 2

On the picture:

Many manufacturers offer the same model for different number lamps So it is not at all necessary to rely on the number of lamps when choosing a lamp - choose a design, and the number of horns can be increased!

Looking for the right light bulb

It is known that an incandescent light bulb for 1 W of power consumption has a luminous intensity of 1 cd, and in a fluorescent (energy-saving) lamp 1 W corresponds to approximately 5 cd. Therefore, to cook food with light, a 60-watt incandescent lamp or fluorescent lamp power 10-15 W.

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>>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;
the sun's rays in bright room(near the window) - 100 lux;
outdoors under 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

Research and production complex "Fotopribor" (Cherkassy) The scope of the enterprise is the development and production of precision mechanics, optoelectronics and optomechanics devices for various purposes, medical and forensic equipment, household goods, office watches of a representative class. HBK Fotopribor develops and produces periscope sights for a variety of artillery installations, gyrocompasses, gyroscopes, optical-electronic equipment for helicopters, armored vehicles, as well as wide range optical equipment and devices for various purposes.

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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Today we will talk about room illumination, how it is measured and with what instruments it can be measured.

Important Factors

One of the important factors that is taken into account both during the construction of a building and during its operation is the level of illumination.

This indicator is very important because it affects the health of a person’s eyes, his ability to work, and his physical and psycho-emotional state.

Therefore, room illumination is included in labor protection provisions.

Building lighting is divided into two components - daylight and artificial.

Natural is daytime solar lighting, which enters the building through technological openings made in it during construction - windows.

Artificial lighting

At night, illumination is produced artificially - with all kinds of electric lamps.

Artificial lighting can also be used in the daytime with weak daylight, as well as in buildings where it is technologically impossible to install the appropriate number of windows, for example, ground floors buildings or basements.

The state of the atmosphere is also taken into account, geographical position.

In what units is illumination measured?

Illumination is measured in lux (Lx) and corresponds to the luminous flux that falls on a certain unit of room area. Often the square meter of the room is used for measurement. Exist .

The calculation of illumination also includes the characteristics of visual performance.

7 levels of visual work have been defined, which take into account the tension in a person’s eyes when performing a particular job.

The greatest illumination is required for rooms in which high-precision work is performed, while the least lighting is installed for control rooms production process.

The conditions for performing work and staying in the premises are also taken into account.

This criterion is divided into 4 subcategories - constant work, periodic work with constant stay in the premises, periodic work with periodic stay and simply monitoring communications.

Types of lighting

4 types are used artificial lighting:

• General (with this lighting, a uniform distribution of the light flux is produced over the entire area of ​​the room. It is achieved by uniformly dispersing light sources over the entire area while maintaining the distance between them);
• Local (used for improved lighting of a separate work area);
• Combined (includes general and local lighting);
• Emergency (rarely used. Designed to provide lighting when the main light source is turned off).

Types of lamps for room lighting

Artificial illumination is achieved through the use of electric lamps, which convert electricity into light flux.

At one time, incandescent lamps were the most common. The wide power range of these lamps made it possible to select a light source with the luminous flux required for certain conditions.

Recently, they have become less in demand because they are economically expensive.

The second type of lamps used for lighting is fluorescent.

These light sources are gas-discharge, in which the luminous flux occurs due to the conversion of an electrical discharge by a phosphor into a luminous flux.

These lamps are more economical because during operation they do not spend part of the energy consumed to generate heat, as happens in incandescent lamps.

The third type of lamps used for indoor lighting is LED. This type of lamp is the most economical.

The economic efficiency of all types of lamps is taken from the calculation of the amount of luminous flux emitted by the lamp and the energy costs that go to provide illumination.

According to this calculation, the table of energy consumption to produce a certain luminous flux looks like this:

Table of lamp power consumption when emitting a certain luminous flux
Lamp type	Incandescent lamp	scenic		Luminous flux (Lm)
Power consumption (W)

Light measurements

Indoor illumination is a quantity that can be measured. Measurements are made using a device - a lux meter.

Illumination measurements are carried out separately for natural and artificial lighting.

The lux meter works on this principle - its design includes a photocell, which receives the light flux.

When hit by light, it releases a stream of electrons, after which the photocell becomes a conductor electric current.

Since the magnitude of the transmitted current is directly proportional to the illumination of the photocell, the conducted current acts as an illumination meter.

The instrument readings are displayed on a scale or display.

Light measurements are taken in different places in the room.

A special feature of using the device is its use only on straight horizontal surfaces and away from electromagnetic sources.

The device first determines general illumination premises, and then the illumination of the workplace itself.

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 the illumination for a work 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 considered compatible in this case. 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?

Today there is no lighting device that would produce a uniform luminous flux, and this does not at all 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.