Saga of LED lamps. Part 1 - History and Terminology
With this article I would like to begin a series of publications devoted to devices that humanity uses for lighting. As is clear from the title, the focus will be on LED lamps, their comparison and the story of why some lamps are good and others are bad, accompanied by good examples of both. Yes, that's right - they are planning measurements, sawing and unwinding. However, before you start something to measure and compare, it is always useful to dive a bit into the history of the issue and talk about what and why should be measured.
First of all, I, as promised, I propose to dive into the story. However, since digging into the dust of the ages is an occupation for an amateur, I hid this part under the spoiler.
So, we will assume that the historical educational program was carried out. Now let's talk about what parameters LED lamps have and why they need to be measured, because LEDs seem to be a pure lighting ideal: they are durable, they practically do not heat up, unlike incandescent lamps, they almost do not contain harmful substances, unlike gas-discharge lamps ; their best specimens outperform gas-discharge lamps in efficiency, while the worst ones are at least much more efficient than comparable incandescent lamps.
However, it is clear that there are no ideals. LEDs also have their own characteristics, which make the technology of their use by a separate engineering world. For example, the incandescent lamp works quite calmly at temperatures of thousands of degrees — LEDs are very demanding to cool: the often claimed life time of hundreds of thousands of hours (for comparison, the incandescent bulb is about a thousand) is achieved only at practically room operating temperature, or at least extremely gentle mode. The effectiveness of LEDs also depends on the quality of their cooling. Like gas-discharge tubes, LEDs cannot be plugged into the network just like that - they need a special driver circuit, the quality of which directly determines the overall quality of the lamp. A separate problem - ensuring compatibility with traditional lamps. The geometry of the incandescent lamp is foreign to LEDs - cooling (which the incandescent lamp did not need) is often difficult; limited volume makes serious demands on the size of the driver, which also affects the performance.
In short, the nature of LEDs makes it necessary to search for various compromises when creating a lamp based on them. The search for a stable ideal of construction, which for the incandescent lamp ended in the first half of the twentieth century, is still in the case of LEDs; Because now on the market are equally often found as a really good products, and obviously unsuccessful models. At the same time, if everything was simple with incandescent lamps, LED lamps have a large number of characteristics, some of which are invisible, or even not obvious to an inexperienced person, but they directly determine the quality of the lamp.
In general, the parameters of LED lamps can be divided into two groups: light and electrical. Attention to the second group is explained by the fact that compact fluorescent and LED lamps are ideologically much closer to washing machines, blenders, razors and other more or less complex household appliances than to “just light bulbs”. With incandescent bulbs, everything is clear - electrically it’s just resistance, so nothing is needed for a long time, everything is clear. In the case of interest to us, on the contrary, we are dealing with a cunning scheme, which ultimately makes a tangible contribution to the overall efficiency; therefore, it is impossible to ignore the electrical parameters here.
The light parameters primarily include the total luminous flux of the lamp ([total] luminous flux). If it is simple, it characterizes how much light it radiates as a whole in all directions. The parameter is interesting and useful, but I must say that he explains little to a mere mortal. The flux is measured in an ideally spherical photometer (but not in a vacuum), and therefore has a somewhat indirect relationship to the behavior of a lamp in an ordinary lamp. The most valuable application for us is the comparison of different lamps according to their light output (about which later). The unit of measurement is lumen (lm).
From the user's point of view, such a parameter as illuminance (illuminance) is an indicator of how bright the lamp illuminates something much more interesting. In fact, this, of course, does not apply to the characteristics of the lamp itself, but depends also on the design of the lamp, the distance from it to the illuminated surface, the location of this surface and other things, like the reflectance of surrounding objects. Therefore, it is difficult to generalize it in any way. Illuminance measured in suites (lux, lx). Light levels are normalized by sanitary rules and regulations.
Light efficiency (luminous efficacy) is an important parameter, the light efficiency of the lamp. Shows how much light the lamp gives per watt of power consumption. Measured in lumens per watt. The absolute theoretical limit of the light output is 683 lm / W. True, this figure is valid only for a monochromatic source of green. For a white light source, which, of course, from the standpoint of general illumination, is of most interest, the theoretical maximum is about 240 lm / W.
Color temperature (CT, CCT - [correlated] color temperature) - if simple, shows the shade of light emitted, from reddish to bluish. Measured in Kelvin. The inscriptions on the packages of the lamps “2700K”, “4200K”, “6500K” are about it. Why is color measured in terms of temperature? The meaning is as follows: if an absolutely black (non-reflecting) body is heated to the specified temperature, it will glow in the same color as the light device on which these figures are written.
Color temperature 2700 - 3000 Kelvin corresponds to the classic shade of incandescent bulbs. Incandescent lamps, by the way, do not give a special choice in this sense - the light in them is obtained as a result of real heating, and it is impossible to heat tungsten to a temperature of more than about three thousand Kelvin - at 3700K it melts and everything in the process must maintain sufficient mechanical strength. In LED and fluorescent lamps, the process of receiving light is not directly related to heating, therefore any shade is possible.
For reference, the color temperature around 4200K corresponds to the morning sun, and the standard daylight is 6500K.
Correlated color temperature is a term applied to line-spectrum sources (gas-discharge lamps) to which the classical definition of color temperature, strictly speaking, is not applicable. In the sense of perception by the eye means the same thing.
In general, the choice of the color temperature of lamps for home lighting is a subjective question. One can only rejoice that modern technologies give us the opportunity to choose.
Color rendering index (CRI, color rendering index) - shows how the colors observed in the light of the artificial light source will be close to those that we see in the light of the sun. Measured in relative units or percent; the ideal value corresponding to sunlight is 100% or 1. This parameter is perhaps the most subjective of the objective lighting parameters. It is tested on specially defined colors, some of which have poetic descriptions like “faded rose color” . If we talk about its practical significance, the thing is this: for sure, many people are familiar with the feeling that the lamp is shining as bright as it is, but at the same time completely “does not illuminate”. The color rendering index is responsible for this. In general, we can say that everything that has a CRI above 80% will illuminate, and not just shine.
In general, the color temperature and color rendering index are perceptually subjective parameters. So here you just have to try and dwell on what you like more.
Pulsations of the luminous flux - due to the fact that the voltage in the network is variable, the lamps may flicker. Low-frequency pulsations are bad for many reasons, one of which is the stroboscopic effect mentioned in the “historical” part. Of course, manufacturers are trying their best to make the luminous flux of the lamp as even as possible. The pulsations of the light flux are measured in percent; on pulsations there are also sanitary norms.
On this with the light parameters of the lamps you can finish and go to the electrical characteristics. Of these, the most interesting are the efficiency of the control circuit and power factor.
With the efficiency of the control circuit, everything is clear - you can put the best LEDs in the lamp, but reduce all their advantages to zero with a current stabilization circuit that consumes more power than the radiators themselves. Efficiency is measured, as is known, as a percentage, calculated as the ratio of output power to input power. The ideal value, of course, is 100%.
The power factor , “cosine phi” (PF, power factor) is a more subtle matter. Let's just say, it shows how intelligently and accurately the device manages the network energy. The fact is that, as already mentioned, the modern advanced lamp is not a resistor, the current consumption thereof is complex; at the same time, the consumed current often does not coincide in form and phase with the mains voltage. Without going into (for now) in detail, I will say that this leads to cunning effects that on a global scale can give a lot of headaches to energy companies. In simple terms, the larger the power factor, the better. It is measured in percent or relative units, the ideal value is 100% or 1. The unit power factor has a simple resistance without capacitive and inductive components. For the network is the most friendly load. The limiting value of the power factor, which can still be considered decent, is 0.8 (GOST 13109-97).
In general, the listed parameters can be considered as the main numerical characteristics describing the quality of the lamp. Of course, it is worth adding here categories of quality of workmanship as well as beauty and “correctness” of circuit design, but these are purely subjective considerations, which, generally speaking, are also reflected in objective parameters. In addition, specifically for LED lamps, it is necessary to evaluate the quality of cooling, since it directly affects the efficiency and service life.
That's all for now. If readers show interest in the topic I have proposed, in the next articles we will evaluate how the parameters, design and circuitry of some common LED lamps relate to eternal ideals.
In connection with the abundance in the article of figures and facts, I note separately that all the statements, the source of which is not explicitly indicated, are taken from Wikipedia (English-speaking or Russian-speaking).
First of all, I, as promised, I propose to dive into the story. However, since digging into the dust of the ages is an occupation for an amateur, I hid this part under the spoiler.
Immerse yourself in the history of lighting.
In the creation of artificial light sources, humanity has come a long way - from fires, torches and oil pans to Arganda lamps , from Arganda lamps to a classical kerosene lamp, and finally to electric lighting, the symbol and main representative of which is incandescent. In fact, the incandescent lamp was an absolutely dominant domestic lighting device for more than a hundred years, from the moment that, in the early twentieth century, through the efforts of Edison, it acquired a modern look. By the way, contrary to conventional wisdom, Edison did not invent it - putting the heated body in a glass flask with an oxygen-free atmosphere first guessed Lodygin, and it is to him that patents belong both to the incandescent lamp itself and to using refractory metals as a heat body, in particular , tungsten ( US Patent No. 575002 ), which is used in light bulbs to this day. The genius of Edison was that he was able to bring the ideas of all who had worked on the problem of electric lighting before to a commercial application that brings real profit; it was thanks to him that the incandescent lamp from the laboratory instrument became a ubiquitous, familiar and convenient source of light.
( Image source )
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Despite the appearance of fluorescent discharge lamps closer to the middle of the twentieth century (the familiar white tubes), it can be said with certainty that no significant changes have occurred in household lighting over the past hundred years. At home, the classic gas-discharge lamps never got accustomed, because they required a much more complex, cumbersome, expensive and sometimes annoyingly buzzing switching circuit, and they blinked at start-up. Of course, they provided significant energy savings compared to incandescent lamps, but in everyday life, comfort is more important than saving ... By the way, in some cases their use was impossible in production as well because the discharge lamp is almost inherent in inertia, in fact it is does not burn continuously, but turns on and off a hundred times per second. It would seem that bad? After all, the human eye is inert enough to ignore this. However, sometimes it can be just dangerous because of the so-called stroboscopic effect: at a certain ratio of the frequency of flickering and rotation of the part, for example, on a lathe, the latter may seem stationary or rotating much slower than the true speed. In particular, if during one half period of the network the part makes a full turn, with each flash of the lamp, the eyes will see it in the same position, and the person will feel that it is stationary. Obviously, this error can end. It is for this reason that the lamps of local illumination of the working area, which can be observed on the machines, never contain gas-discharge lamps (GOST 12.2.009-99).
( Wikipedia )
Of course, modern circuitry is able to solve all the problems listed (and rather successfully solves them in "savings"). However, by the time it became possible, an event occurred in the world of illumination comparable to the invention of incandescent lamps — white LEDs were invented and brought to industrial production.
The first known message about light emission by a solid-state semiconductor device dates back to 1907, the year when Henry Round observed a glow of a non-thermal nature when current passes through a contact of a metal and silicon carbide; later, in 1923, Oleg Losev independently came to the same results and created what could already be called a LED. Both researchers fully appreciated the scale of their discoveries, but the level of science at that time did not allow them to move further along the path of applying the detected effects to light. The first LED, which was able to leave the laboratory, was invented by Nick Holonyak in the 1962nd year. However, the lighting was still very far away - the light emitted was tenacious and limited to red and shades of orange.
Over time, scientists have significantly improved the characteristics of LEDs - expanded the set of possible colors of light up to green, increased the light output and the brightness of the crystals. But the real breakthrough came in 1994, when Shuji Nakamura invented a blue LED, suitable for industrial production. Only then for the first time it became possible to get a white glow, combining the already existing red and green with freshly invented blue crystals. Soon (in the 1996th year) the white LED, which is classic today, was invented - a blue crystal coated with phosphor, re-emitting some of the energy of blue light in the yellow area. This is how modern lighting LEDs work - the mixture of blue light from a blue crystal and a yellow one from a phosphor gives white light.
( Image source )
( Image source )
')
Despite the appearance of fluorescent discharge lamps closer to the middle of the twentieth century (the familiar white tubes), it can be said with certainty that no significant changes have occurred in household lighting over the past hundred years. At home, the classic gas-discharge lamps never got accustomed, because they required a much more complex, cumbersome, expensive and sometimes annoyingly buzzing switching circuit, and they blinked at start-up. Of course, they provided significant energy savings compared to incandescent lamps, but in everyday life, comfort is more important than saving ... By the way, in some cases their use was impossible in production as well because the discharge lamp is almost inherent in inertia, in fact it is does not burn continuously, but turns on and off a hundred times per second. It would seem that bad? After all, the human eye is inert enough to ignore this. However, sometimes it can be just dangerous because of the so-called stroboscopic effect: at a certain ratio of the frequency of flickering and rotation of the part, for example, on a lathe, the latter may seem stationary or rotating much slower than the true speed. In particular, if during one half period of the network the part makes a full turn, with each flash of the lamp, the eyes will see it in the same position, and the person will feel that it is stationary. Obviously, this error can end. It is for this reason that the lamps of local illumination of the working area, which can be observed on the machines, never contain gas-discharge lamps (GOST 12.2.009-99).
( Wikipedia )
Of course, modern circuitry is able to solve all the problems listed (and rather successfully solves them in "savings"). However, by the time it became possible, an event occurred in the world of illumination comparable to the invention of incandescent lamps — white LEDs were invented and brought to industrial production.
The first known message about light emission by a solid-state semiconductor device dates back to 1907, the year when Henry Round observed a glow of a non-thermal nature when current passes through a contact of a metal and silicon carbide; later, in 1923, Oleg Losev independently came to the same results and created what could already be called a LED. Both researchers fully appreciated the scale of their discoveries, but the level of science at that time did not allow them to move further along the path of applying the detected effects to light. The first LED, which was able to leave the laboratory, was invented by Nick Holonyak in the 1962nd year. However, the lighting was still very far away - the light emitted was tenacious and limited to red and shades of orange.
Over time, scientists have significantly improved the characteristics of LEDs - expanded the set of possible colors of light up to green, increased the light output and the brightness of the crystals. But the real breakthrough came in 1994, when Shuji Nakamura invented a blue LED, suitable for industrial production. Only then for the first time it became possible to get a white glow, combining the already existing red and green with freshly invented blue crystals. Soon (in the 1996th year) the white LED, which is classic today, was invented - a blue crystal coated with phosphor, re-emitting some of the energy of blue light in the yellow area. This is how modern lighting LEDs work - the mixture of blue light from a blue crystal and a yellow one from a phosphor gives white light.
( Image source )
So, we will assume that the historical educational program was carried out. Now let's talk about what parameters LED lamps have and why they need to be measured, because LEDs seem to be a pure lighting ideal: they are durable, they practically do not heat up, unlike incandescent lamps, they almost do not contain harmful substances, unlike gas-discharge lamps ; their best specimens outperform gas-discharge lamps in efficiency, while the worst ones are at least much more efficient than comparable incandescent lamps.
However, it is clear that there are no ideals. LEDs also have their own characteristics, which make the technology of their use by a separate engineering world. For example, the incandescent lamp works quite calmly at temperatures of thousands of degrees — LEDs are very demanding to cool: the often claimed life time of hundreds of thousands of hours (for comparison, the incandescent bulb is about a thousand) is achieved only at practically room operating temperature, or at least extremely gentle mode. The effectiveness of LEDs also depends on the quality of their cooling. Like gas-discharge tubes, LEDs cannot be plugged into the network just like that - they need a special driver circuit, the quality of which directly determines the overall quality of the lamp. A separate problem - ensuring compatibility with traditional lamps. The geometry of the incandescent lamp is foreign to LEDs - cooling (which the incandescent lamp did not need) is often difficult; limited volume makes serious demands on the size of the driver, which also affects the performance.
In short, the nature of LEDs makes it necessary to search for various compromises when creating a lamp based on them. The search for a stable ideal of construction, which for the incandescent lamp ended in the first half of the twentieth century, is still in the case of LEDs; Because now on the market are equally often found as a really good products, and obviously unsuccessful models. At the same time, if everything was simple with incandescent lamps, LED lamps have a large number of characteristics, some of which are invisible, or even not obvious to an inexperienced person, but they directly determine the quality of the lamp.
In general, the parameters of LED lamps can be divided into two groups: light and electrical. Attention to the second group is explained by the fact that compact fluorescent and LED lamps are ideologically much closer to washing machines, blenders, razors and other more or less complex household appliances than to “just light bulbs”. With incandescent bulbs, everything is clear - electrically it’s just resistance, so nothing is needed for a long time, everything is clear. In the case of interest to us, on the contrary, we are dealing with a cunning scheme, which ultimately makes a tangible contribution to the overall efficiency; therefore, it is impossible to ignore the electrical parameters here.
The light parameters primarily include the total luminous flux of the lamp ([total] luminous flux). If it is simple, it characterizes how much light it radiates as a whole in all directions. The parameter is interesting and useful, but I must say that he explains little to a mere mortal. The flux is measured in an ideally spherical photometer (but not in a vacuum), and therefore has a somewhat indirect relationship to the behavior of a lamp in an ordinary lamp. The most valuable application for us is the comparison of different lamps according to their light output (about which later). The unit of measurement is lumen (lm).
From the user's point of view, such a parameter as illuminance (illuminance) is an indicator of how bright the lamp illuminates something much more interesting. In fact, this, of course, does not apply to the characteristics of the lamp itself, but depends also on the design of the lamp, the distance from it to the illuminated surface, the location of this surface and other things, like the reflectance of surrounding objects. Therefore, it is difficult to generalize it in any way. Illuminance measured in suites (lux, lx). Light levels are normalized by sanitary rules and regulations.
Light efficiency (luminous efficacy) is an important parameter, the light efficiency of the lamp. Shows how much light the lamp gives per watt of power consumption. Measured in lumens per watt. The absolute theoretical limit of the light output is 683 lm / W. True, this figure is valid only for a monochromatic source of green. For a white light source, which, of course, from the standpoint of general illumination, is of most interest, the theoretical maximum is about 240 lm / W.
Color temperature (CT, CCT - [correlated] color temperature) - if simple, shows the shade of light emitted, from reddish to bluish. Measured in Kelvin. The inscriptions on the packages of the lamps “2700K”, “4200K”, “6500K” are about it. Why is color measured in terms of temperature? The meaning is as follows: if an absolutely black (non-reflecting) body is heated to the specified temperature, it will glow in the same color as the light device on which these figures are written.
Color temperature 2700 - 3000 Kelvin corresponds to the classic shade of incandescent bulbs. Incandescent lamps, by the way, do not give a special choice in this sense - the light in them is obtained as a result of real heating, and it is impossible to heat tungsten to a temperature of more than about three thousand Kelvin - at 3700K it melts and everything in the process must maintain sufficient mechanical strength. In LED and fluorescent lamps, the process of receiving light is not directly related to heating, therefore any shade is possible.
For reference, the color temperature around 4200K corresponds to the morning sun, and the standard daylight is 6500K.
Correlated color temperature is a term applied to line-spectrum sources (gas-discharge lamps) to which the classical definition of color temperature, strictly speaking, is not applicable. In the sense of perception by the eye means the same thing.
In general, the choice of the color temperature of lamps for home lighting is a subjective question. One can only rejoice that modern technologies give us the opportunity to choose.
Color rendering index (CRI, color rendering index) - shows how the colors observed in the light of the artificial light source will be close to those that we see in the light of the sun. Measured in relative units or percent; the ideal value corresponding to sunlight is 100% or 1. This parameter is perhaps the most subjective of the objective lighting parameters. It is tested on specially defined colors, some of which have poetic descriptions like “faded rose color” . If we talk about its practical significance, the thing is this: for sure, many people are familiar with the feeling that the lamp is shining as bright as it is, but at the same time completely “does not illuminate”. The color rendering index is responsible for this. In general, we can say that everything that has a CRI above 80% will illuminate, and not just shine.
In general, the color temperature and color rendering index are perceptually subjective parameters. So here you just have to try and dwell on what you like more.
Pulsations of the luminous flux - due to the fact that the voltage in the network is variable, the lamps may flicker. Low-frequency pulsations are bad for many reasons, one of which is the stroboscopic effect mentioned in the “historical” part. Of course, manufacturers are trying their best to make the luminous flux of the lamp as even as possible. The pulsations of the light flux are measured in percent; on pulsations there are also sanitary norms.
On this with the light parameters of the lamps you can finish and go to the electrical characteristics. Of these, the most interesting are the efficiency of the control circuit and power factor.
With the efficiency of the control circuit, everything is clear - you can put the best LEDs in the lamp, but reduce all their advantages to zero with a current stabilization circuit that consumes more power than the radiators themselves. Efficiency is measured, as is known, as a percentage, calculated as the ratio of output power to input power. The ideal value, of course, is 100%.
The power factor , “cosine phi” (PF, power factor) is a more subtle matter. Let's just say, it shows how intelligently and accurately the device manages the network energy. The fact is that, as already mentioned, the modern advanced lamp is not a resistor, the current consumption thereof is complex; at the same time, the consumed current often does not coincide in form and phase with the mains voltage. Without going into (for now) in detail, I will say that this leads to cunning effects that on a global scale can give a lot of headaches to energy companies. In simple terms, the larger the power factor, the better. It is measured in percent or relative units, the ideal value is 100% or 1. The unit power factor has a simple resistance without capacitive and inductive components. For the network is the most friendly load. The limiting value of the power factor, which can still be considered decent, is 0.8 (GOST 13109-97).
In general, the listed parameters can be considered as the main numerical characteristics describing the quality of the lamp. Of course, it is worth adding here categories of quality of workmanship as well as beauty and “correctness” of circuit design, but these are purely subjective considerations, which, generally speaking, are also reflected in objective parameters. In addition, specifically for LED lamps, it is necessary to evaluate the quality of cooling, since it directly affects the efficiency and service life.
That's all for now. If readers show interest in the topic I have proposed, in the next articles we will evaluate how the parameters, design and circuitry of some common LED lamps relate to eternal ideals.
Note
In connection with the abundance in the article of figures and facts, I note separately that all the statements, the source of which is not explicitly indicated, are taken from Wikipedia (English-speaking or Russian-speaking).
Source: https://habr.com/ru/post/362653/
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