LED lamp based on cob technology. Types and types of LEDs: classification, characteristics, purpose. Short operating time
Knyazev O.V., Stroy-TK Group of Companies, May 2017
Currently, the LED lighting market in Russia is experiencing its boom; high-tech expensive models of lamps and spotlights are presented for sale, guarantee period which are 3-7 years old, as well as cheap LED products that are unlikely to work without breakdowns for at least 1 year. Let's try to make sense of this multitude of proposals.
Where do cheap disposable “crafts” come from?
Paradoxically, it is the Customer himself who is to blame for the presence of a large number of offers of cheap consumer goods LED lamps, because the main selection criterion for the Customer is Cost.
The situation is repeating itself, as it happened before: if there is a demand for cheap products, manufacturers from the Middle Kingdom will provide supply! Since no one has a monopoly on imports from China, competitors are beginning to demand that manufacturers constantly, from batch to batch, reduce purchase prices in order to simply beat out competitors in the market with a low price. However, there are reasonable limits to everything and a constant reduction in the cost of products while maintaining all the basic characteristics is simply impossible. So the game begins to reduce performance characteristics, reliability, etc. - just to sell lighting equipment, providing a minimum warranty period. And this despite the fact that crazy operating times are announced for LEDs - from 50 to 100 thousand hours.
What is COB
COB technology, more recently MCOB (Multi Chip-on-Board) - translated as “Crystal on a Board”. Considered to be the most advanced LED technology to date.
Briefly, it can be described as follows: placement of crystals on a board without cases and ceramic substrates, as well as covering all these crystals with a common layer of phosphor. LED crystals are located very close to each other - the placement density can reach 70 crystals per 1 cm 2, i.e. the crystals practically merge into a single field and the glow of the matrix is very uniform, individual points of the crystals are indistinguishable.
An important advantage of the technology is the quality of the emitted light. Objects illuminated by COB-matrix lamps have a clear shadow boundary due to the uniform distribution of the light flux. Lamps based on SMD LEDs, unfortunately, cannot boast of such contrast due to the large number of individual crystals and reflectors widely spaced in space.
The energy efficiency of COB matrices can reach 170 Lm/W.
Benefits of COB
The main advantages of MCOB technology are:
- High luminous efficiency (more than 100 lm/W);
- Possibility of achieving high luminous flux intensity with relatively small dimensions;
- Compatible with various drivers, incl. with dimming;
- Uniformity of light flux, absence of shadow effect;
- Compactness, small size, availability of various shapes;
- Possibility of producing matrices of any color temperature from 2700K to 7000K;
- Color rendering index up to 90Ra;
Disadvantages of COB
The main disadvantage of COB technology is the mandatory provision of good heat removal from a powerful COB matrix, which is difficult to ensure, since the matrix area is small, and it is difficult to remove excess heat from a small contact area.
This is where the catch lies: a cheap, and therefore initially low-quality, COB matrix, mounted on a cooling radiator without proper adjustment and treatment of the mating surfaces, does not cool enough, begins to overheat and, ultimately, burns out.
As confirmation, we can cite the following fact: not so long ago, we received 57 units at the service center for diagnostics and repair. LED spotlights(COB) power 100W. Judging by their appearance (see photo), they are from the cheap GS Light series.
After diagnostics, it was revealed that in the vast majority of spotlights (49 pieces), the COB LED matrix failed, and in the remaining 8 cases, the LED driver failed.
What is SMD
SMD (Surface Mounting Device) technology can literally be translated as “surface mounted device”.
The main difference between this technology and the "traditional" through-hole technology is that the components are mounted on the surface of the board. This ensures smaller design dimensions, better heat dissipation, and design variability. This design Today it is the most common in lighting and is used in almost all types of light sources.
Today, SMD technology is the most common in LED lighting and is used in almost all types of lamps.
This technology was created to organize powerful diffuse lighting, which is achieved by distributing a significant number of small LEDs over the entire area of the lamp (there are up to 700 pieces in one product), which makes it possible not to use any additional optics in the lamps, only ordinary protective glass lamp body. To increase the degree of dispersion (for example for rooms with computer equipment), a milky, prismatic or microprismatic diffuser is used.
Since the LEDs are located on a large aluminum strip, and the distance between them is quite large, cooling the LEDs does not cause much difficulty, hence the durability of SMD strips if they are properly powered.
Among the disadvantages of lamps with SMD lines, it should be noted that they are very difficult to repair, since when one LED fails, the entire line stops lighting, and replacing an SMD LED yourself is a rather labor-intensive task. Replacing the entire line is already financially expensive. To be fair, it must be said that most manufacturers of LED lamps in Russia, when a warranty case arises, replace the entire line.
COB and SMD Applications
1. General case
I would make the section this way: if the form factor of the lamp body allows you to place a sufficiently large cooling radiator, then you can use COB LED lamps, limiting their power to 30 W. All lighting equipment with higher power is exclusively SMD. But in general ideal option the introduction of LED lighting will become.
2. I handed over the object and forgot
If the task is precisely this - to hand over the object and run away, then, of course, you need to use cheap lamps or spotlights on a high-power COB matrix. The time they work should be enough for you to disappear from sight... :)
3. Short working time
If a lamp or spotlight works occasionally, turning on for a few minutes (for example, it is equipped with a presence sensor and turns on only when people pass), you can safely choose COB. The matrix simply will not have time to overheat.
4. Organization of temporary lighting.
To organize temporary lighting (for example, at a construction site during finishing work), I would recommend using COB floodlights with a power of 20 - 30 W.
5. Lighting for warehouses and industrial premises
In warehouses, industrial buildings and premises, powerful lamps suspended at a high (6-12 meters) height are usually used. For their electric lighting, it is strongly recommended to use lamps made on SMD LED lines. When choosing lamps, pay special attention to the presence of clearly visible radiators, the purpose of which is to dissipate excess heat into the environment.
In the last decade, lighting companies have gained great popularity COB LEDs. This is because COB technology allows high-power directional white light LEDs to be designed and mass-produced from conventional light-emitting crystals in high volume, mass production. COB is an abbreviation, i.e., a reduction to the first letters of the English phrase chip-on-board. Translated into Russian as a crystal or element on a board.
The idea of this method is simple and as old as the Egyptian pyramids: if the strength of one person or the light of one LED is not enough, then attract a hundred people to pull the stone for the pyramid. Or place a dozen light-emitting crystals in one housing. COB LED This is a rectangular or round plate of yellow color, housed in a housing with a transparent cover or covered with a lens of secondary LED optics. The lens forms the desired directional pattern for the light flow and protects the COB structure from dust, water, mechanical stress, etc.
The essence of COB technology
Finished LED chips without housings are glued onto a heat-conducting artificial sapphire substrate or soldered onto a semiconductor silicon wafer. Depending on the operating voltage, the chips are connected in series circuits. For 9 V – 3 pcs., 12 V – 4 pcs. etc. The chain is powered by a current of one magnitude - the nominal operating current for crystals of this type, for example, 20 mA. Serial chains are connected in parallel, gaining power or luminous flux. Then the blue light LED crystals are coated with a yellow phosphor. This is how you dial heavy duty LEDs COB.
What does the phrase mean SMD COB LEDs? This is a COB matrix housed in an SMD package. These housings are designed for automated installation of ERE (electro-radio elements) directly onto the surface printed circuit board. COB is a set of technological operations for the production of high-power and ultra-high-power LEDs in the form of a single matrix. The matrix consists of tens or hundreds of crystals.
As the power of LEDs increased, manufacturers began to look for ways to improve heat dissipation. As a result, COB LED technology emerged, which makes it possible to create compact and powerful light sources with high optical density, from which the excess heat is removed by the housing. These LEDs are built into lamps and spotlights for lighting industrial and residential premises, and architectural lighting.
In COB LEDs, crystals without a housing or substrate are located close to each other, connected in series in parallel and covered with a single layer of phosphor. Up to 70 chips can be placed on 1 cm2 of board, as a result the optical density is significantly increased (the glow is uniform, without dots). The board can have different sizes; excess heat is lost through the case, regardless of the number of diodes.
The shape of the module can be rectangular, square, round, oval, which allows it to be installed in almost any lighting fixture. Power depends on area, high brightness can be achieved with minimal module sizes. This design does not create shadows, the surface is illuminated evenly. These LED sources work well with all ballasts, brightness and color dimmers, and automatic lighting control systems.
Attention! To obtain more power, you can use a miniature COB LED matrix instead of a volumetric SMD matrix.
Production process
The COB LED manufacturing process consists of many steps:
- manufacturing of substrates;
- applying a composition to them that ensures adhesion;
- crystal installations;
- hardening of the adhesive coating;
- plasma cleaning from contaminants;
- electrical connection of LEDs;
- coating the crystals with a phosphor, providing sealing.
The printed circuit board has three layers: a metal base, a dielectric, a layer that conducts current.
For a long time, the implementation of SOV technology was prevented by the lack of a method for uniformly applying an adhesive composition to substrates. It must be of a certain thickness; neither increase nor decrease is allowed. In the first option, the thermal contact with the body is broken, in the second, the crystals come off.
In 2009, the magnetron sputtering method was proposed, which makes it possible to create thermal contact of a quality superior to that created on SMD printed circuit boards. The new method was called MCOB (Multi Chip-onBoard). At the moment, all the best manufacturers use it.
Attention! Even in scientific publications, COB and MCOB have the same meaning.
SOV technology allows you to create matrices of any shape without additional optical elements.
Let's express our point of view on this dilemma, which is beginning to resemble a debate about which is better, iOS or Android. There is no clear answer to this question. It is necessary to clearly understand the purpose of the lamp, which uses a diode matrix. For some, COB will be better, for others - SMD.
COB for little powerful lamps directional light
For example, COB clearly wins in commercial directional lighting fixtures. Such as track lights, downlights and other types of accent lighting.
For diffuse commercial lighting, conventional lighting is more suitable. LED Strip Light or a ruler mounted around the perimeter of the lamp body under the diffuser. COB matrices also behave quite well in street floodlights with a power of up to 50 watts.
SMD for industrial dome lights over 50W
As for the lighting of industrial enterprises, for example, in industrial LED lamps the bell
It is almost impossible to find a COB matrix (see figure on the right) from world-famous advanced manufacturers, although a few years ago everyone loved such experiments.
Industrial LED dome lamps with a COB matrix are much cheaper than a lamp with an SMD diode board, such as industrial dome lamps.
This is due to the fact that a COB matrix with diodes from the same manufacturer costs 30-50% less, which reduces the cost of the lamp. The downside, according to reviews from most well-known manufacturers of industrial and street lighting, is the frequent replacement of COB matrices under warranty if the lamp power is more than 50 W.
At one of the factories with which we cooperate, we were told a story about how an industrial LED bell lamp with a high-quality heat dissipation system and a high-quality COB diode was left turned on with the chip down on the table, and within 2 hours the table caught fire.
Real experience
From our personal practice, we know the story of how a power engineer at a large enterprise, in order to save money at the expense of quality, bought industrial dome lamps with COB diodes and now he has to pay for his wrong decision: every year to change the diode boards in 15-20% of the lamps .
In order not to get scolded by his superiors for making the wrong choice at one time, he asks to be billed for fluorescent lamps and various electrical consumables instead of COB matrices, in order to hide real expenses.
COB Diode Degradation
We should also not forget about the real degradation of diodes in high-power industrial luminaires, which, according to user observations, is higher for high-power luminaires with COB elements. But very rarely does anyone carry out annual measurements of room illumination.
Diode counterfeiting: How to identify unscrupulous manufacturers of industrial lighting fixtures?
Glare effect of COB diodes
Another observation from users is the fact that industrial COB LED dome lights in warehouses and workshops produce a stronger glare effect, which makes it difficult for personnel to work at heights.
Expert opinion: “Our opinion: LED luminaires with COB matrix are The best decision for accent light and moderate power luminaires up to 50W. The only exceptions are multi-module systems, in which each module is a separate COB matrix of moderate power. For lighting of more than 50 watts, it is better to use industrial bell lamps with an SMD matrix. Moreover, the greater the number of diodes per 1 watt of power, the better,” says Alexey Frolov, lighting engineer at Grandenergoproekt.
