LED design provides exciting opportunities for all the talk about this often hindered by such words: thermal management. "When incandescent bulbs can burn calories by radiation, led street lights price has almost no infrared heat." Predock technology marketing director Michael Gershowitz said. Therefore, LED must be heat by heat conduction, otherwise there is a risk: brightness, lifetime, color stability and performance will be weakened.
But time and market demand will always have a way to advance to a node technology that will soon become a fixture thermal management design considerations late, rather than an obstacle. With the continuous iteration LED luminous efficiency has continued to grow exponentially, now has more than 50% efficiency LED, namely: they will more than light energy is converted into heat. Most OEM manufacturers have abandoned the original simple to use LED lighting to replace the traditional approach to production of tailor-made according to the characteristics of the LED light source and optimized lighting. And now the LED can be "at higher temperatures for longer, and the brightness does not decay." Mark Hand Acuity Brands Lighting indoor new product development and technical director said this.
Progress, manufacturers of LED technology and lighting design can boast something more than that. Thermal management strategies have been in progress and flourish. Although passive cooling and active cooling is still the main choice, but other innovative technologies are added.
More than 90% of the LED lamp uses passive cooling. Under this policy, the heat of the LED package via the highly heat conductive material in direct physical contact with the heat sink to transfer out manner. "Aluminum - usually by extrusion or die-casting with fins become round - because of its light weight, inexpensive and easy to manufacture, and is the standard material used as a heat sink" Christopher Reed Xicato strategic partner manager . Currently, manufacturers are more reliable because of its pro-gaze passive radiator. "Even if not exactly the same, they behave 50,000 hours or 20 years after the first day is not far in." Reed says.
Passive cooling
But even if it is a tested and proven reliable solution can be improved. The designers cleverly treated by optimizing the radiator fin thickness and spacing, while passive cooling strategy also developed a new form - column radiator fins. Unlike extruded blade is similar to the inverted radiator fins column filled with a large number of round table legs, while the LED device is attached to the surface of the table.
Fin
Reed said cylindrical fin making the heated air rises and then around the fin column effluent unhindered. On some of the characteristics of the rotatable lamp has advantages, such as track lights. "When you would a standard extruded fin radiator tilt, air can not be in the same direction or axis gravity flow, because it is always going to go into the fin." Reed says.
Lighting manufacturers have begun to be integrated into a light body cooling solutions. With this strategy, rim lighting installed in ceiling insulation system can either play a modified role, but also the heat. Similarly, cree Aeroblades sculptural series of street action that fin played, not the "vase" so simple.
"With the LED becomes more efficient, the required heat sink size and weight are also getting smaller and smaller." Mark McClear CREE applications engineering vice president, said. Following this, the material and transportation costs will be reduced. "When the LED becomes more efficient, everything is moving in the right direction in the development." McClear said.
Active cooling
Passive thermal management convenience often been plagued by heavy radiator. This volume will be a problem for small lamps, outdoor lighting is concerned for the seal also inappropriate and not feasible for high lumen downlight. Forced to rely on active cooling air circulation, rather than natural convection, "so that emit more heat in a much smaller space," Hand said.
Active cooling itself requires more moving parts, increasing costs, they were the OEM accept slower pace. However, recent developments make active cooling solutions become more efficient and reliable.
In fact even active cooling solution - fan - has also made great progress. According Xicato of Reed explained that the long-configured solution is to either use plain bearings - typically made of plastic or polymer material composition, and vulnerable to the impact of dust accumulation and the time - or is a more durable metal ball bearing system.
Active cooling
In order to eliminate friction between the fan bearings and drive shaft located in Brea, California introduced a thermal design company Sunon Maglev technology. To deal with dust gathering, the company has also developed a two-way rotary technology, that the machine in the first few seconds of running the fan reversal, "to remove dust from the fan on", Reed said.
Noise is active cooling incur another reason to complain about. For example, in a room equipped with track lights, the average volume of each lamp in 15-30 decibels, the noise caused by active cooling is obvious. "Sounds like a beehive," Reed said. Located in Farmington, Conn. Ebm-Papst company provides a run-time only 7 db fan, this is the quietest ever seen Reed fan products.
For manufacturers who are still suspected of fans, Austin, Texas Nuventix provide a pulsed silicon membrane technology that can be discharged into the air from the LED heat sink, and thus, the volume can be reduced to a separate radiator passive third cooling solution. Synthetic jet technology, or call SynJet, "without any rotating parts or friction." Tom Dalton, senior vice president of marketing, said Nuventix. Instead, it uses the led street lighting fixture power supply 50 times per second, making the film fibrillation - he estimated power consumption of about 0.35-1W-- these adiabatic pulse generating turbulent air convection cooling to form a better way than this by a fan laminar airflow generated better. Reed said. This technology, SynJet can 5-year warranty, can extend beyond the limits of silicon film 10%, Nuventix of Dalton said.
Although some manufacturers for active cooling on the moving parts are still worried, but most agree that active cooling is more efficient than passive cooling. "The more heat and silently, the situation will be better." Gershowitz said.
Hybrid heat pipe
Heat pipe technology is mature PC with cooling mechanism, combined with active and passive cooling solution features both, also caused the OEM and lighting manufacturer interest. In essence, the heat pipe is sealed by a metal pipe, internal thermal fluid filled structure, which will heat away from the LED at the cooling system and sent to the remote. Despite the distance from the heat source and the heat sink to increase the effectiveness of the system will be weakened, still makes the overall heat pipe assembly apart. "This separation is an excellent design opportunities." Gershowitz said. For example, the heat pipe within a compact lifting fixtures can transfer heat to the ceiling of a creative ceiling. "Designers can come up with some very attractive program." He said.
5 hybrid heat pipe
FrigoDynamics company has a number of new techniques applied to this technology inside. The German company has created an effective hybrid cooling technology, they will pass through a passive heat pipe radiator metal blade geometry by strategically shaping the inside, so that the heat is maximized. "Heat pipe heat from the radiator side is discharged to the elements on the other side." Reed says. "It's very efficient in the discharge of heat, and the heat sink can get up and down very uniform and constant temperature."
Yet proven technology to show its mettle in practice, has also attracted interest from a number of curious vendors. Sandia Corp. Sandia has been a long-term commitment to the development of the radiator, which is a single piece of metal fan, relying on air bearings rotate, thereby eliminating the potential for physical bearing failure.
If you talk and cooling the dielectric material, the discussion on thermal management strategy is not comprehensive, it is the material between the LED and its heat sink metal back in the tiny gap filling. The choice of the thermal pad material is filled in the air gap, the heat transfer is crucial for the LED's. The phase change material is a plausible, effective, and whether plastic or metal materials can be selected thermal substrate, Gershowitz said.
Cambridge Nanatherm also focus on the complex problems of these micro-level. The British company has recently introduced a nano-ceramic dielectric layers for LED PCB board using thermal conductivity of 7W / mK. MBPCBs typically epoxy filler, its thermal conductivity between 1-3W / mK. Nanotherm said their MBPCBs heat derived from the LED chip efficiency is 20% higher than the aluminum PCB market.
In addition to advances in thermal management strategies, with the LED efficiency rate of increase of McClear --CREE 2020 will reach 65% - LED heat will not be a problem on the lighting design. Acuity's Mark Hand forecast: low power LED will turn to their own strategically distributed heat, no longer even need a dedicated thermal management strategies. "In the top of the scale, people will try and get more lumens from a smaller space, they will begin to focus on the thermal conductivity of polymer." This can be molded into a wide range of LED package, he said.
Puri's Gershowitz that, even if progress in LED efficiency, thermal management remains appropriate to retain. "Every step forward ...... is not reduced in order to reduce power or cooling solution, OEM manufacturers will use the same cooling solution, but with a larger light source." The good news is: the speed of development of thermal management, will allow OEM manufacturers and lighting solid-state lighting manufacturers will expand to more markets, did not need to worry about burn.
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