Archive for June, 2011

LEDs and OLEDs Power Innovative Large-scale Displays

29 Jun

Mitsubishi Electric utilizes OLEDs to build a 6m spherical display, while Panasonic has created the world’s largest HDTV using LEDs at Charlotte Motor Speedway.

The Geo-Cosmos display

Visitors to the National Museum of Emerging Science and Innovation in Tokyo, Japan can now enjoy a 6m-diameter globe display that Mitsubishi Electric built utilizing 10,362 organic light-emitting diode (OLED) panels. And US auto racing fans that visit Charlotte Motor Speedway in North Carolina will experience instant replays and leaderboard statistics on a high-definition (HD) video board that stands 200-ft wide and 80-ft tall that Panasonic constructed using 9 million LEDs.

The Mitsubishi Geo-Cosmos display hangs 18m above the floor in the Tokyo museum replacing an older globe that was lit by LEDs. Mitsubishi says that the display can project 10 million pixels – 10 times more than the older LED globe. The new display was commissioned to commemorate the 10th anniversary of the museum.

Mitsubishi, along with partners Dentsu, GK Tech, and Go and Partners, constructed the globe using individual Mitsubishi Diamond Vision OLED panels that measure 96×96 mm. The panels feature a 3-mm dot pitch for each RGB pixel. The panels are mounted on an aluminum skin that forms the sphere.

The museum will use the global display to project the earth and to present other symbiotic scenes. For example, the display can project scenes of clouds and earth images captured from a meteorological satellite.

Dale Earnhardt Jr debuts HD board

The NASCAR Sprint Cup All-Star race on May 21 served as the debut for the largest HD video board in the world. Panasonic constructed the 16,000-square-foot screen using 158 panels made with LEDs.

The display stands 110 ft above the race track centered along the backstretch of the course. It is capable of playing video with 720p resolution.

The speedway said that the new board uses “280 times more LED bulbs than the Times Square Ball” that is used to celebrate the arrival of the New Year annually in New York City. The speedway noted that the New York ball can be seen from 50 blocks away and expects fans seated along the entire front stretch to have a clear view of the HD board.

The speedway conducted an operational debut of the HD board with the help of Dale Earnhardt Jr – one of NASCAR’s biggest stars. Earnhardt demonstrated the HD capabilities playing a racing simulation video game displayed on the board.

“The Coca-Cola 600 [a May race at the track] is one of the best events we have all year long. Now fans can get a ticket to the race and have the experience of the live event with the comfort of their own TV at home with this big TV,” Earnhardt Jr. continued. “This place just keeps getting better.”

Indeed the speedway presented live action, video replays, race statistics, and interactive entertainment on the board. “This giant Panasonic HDTV will be a game changer for our fans on race day,” said Marcus Smith, president and general manager of the speedway. “It will give them a whole new way to experience a NASCAR event at Charlotte Motor Speedway.”


LED Driver IC Market Benefits from Sales of LED TVs and Lamps

29 Jun

Strategies Unlimited says that the market for LED driver ICs will grow at a CAGR of 12% between 2010 and 2015, driven by the demand for LED TV backlights and replacement LED lamps.

LED driver IC sales will reach nearly $3.5 billion in 2015 from nearly $2 billion in 2010, a compound annual growth rate (CAGR) of 12%, according to Mountain View, CA-based market research firm Strategies Unlimited.

These are among the findings in Strategies Unlimited’s new report “LED Driver ICs – 2011.” Sales for LCD backlights will dominate through the period, with growth from edge-lit TVs and monitors. LED lighting applications will be the “next big thing” for LED drivers and driver ICs, beginning with LED replacement bulbs, as a response to improvements in technology and the phase-out of incandescent bulbs.

LED driver IC revenues are threatened, however, by continued integration into fewer ICs, as well as by competition from organic LEDs (OLEDs), compact fluorescent lamps, and other technologies.

Severe price erosion for driver ICs will limit the revenue growth as volumes increase, but new, higher-priced ICs are appearing that reduce the overall bill of materials and also help maintain the average price of the ICs.

Also, AC-LED products minimize the driver and some eliminate the driver IC, but will not have a significant impact on overall revenues through the period, and may even help accelerate adoption of LED lighting.

Lighting market

The production value of drivers for lighting will see strong 40% compound annual growth through the period. The driver is defined as the entire LED circuit, including the driver IC but excluding the LEDs. Innovations in driver design will help take LED lighting mainstream, but the market will quickly shake out those who cannot meet strict goals for dimming, efficiency, power factor, and price.

To meet these goals, large and small companies are bringing innovations to market, such as digital control and novel high-voltage designs. Industry and government are moving toward more standardized specifications that will reduce manufacturing costs and accelerate adoption.

The top 10 LED driver IC suppliers hold more than 55% of revenues, with about 30 IC suppliers and captive manufacturers sharing the other 44%. With the acquisition of National Semiconductor by Texas Instruments, TI is now the number one supplier of LED driver ICs. Winners will be those who can keep delivering innovative products at competitive prices. Fabrication with leading-edge, high-voltage BCD processes and 8-inch (or larger) wafers will play a key role.


Thermal Management of High-power LEDs

15 Jun

High power light-emitting diodes (LEDs) are likely to replace other technologies such as incandescent and fluorescent bulbs in signaling, solid state lighting, and vehicle headlights because they save energy and extend the light’s lifetime. LEDs that use from 500 milliwatts to as much as 10 watts in a single package have become standard, and researchers expect to use even more power in the future. Some of the electricity in an LED becomes heat rather than light. If that heat is not removed, the LEDs run at high temperatures, which not only lowers their efficiency, but also makes the LED more dangerous and less reliable. Thus, thermal management of high power LEDs is a crucial area of research and development.

Heat transfer procedure

In order to maintain a low junction temperature to keep good performance of an LED, every method of releasing heat from LEDs should be considered. Conduction, convection, and radiation are the three means of heat transfer. Typically, LEDs are encapsulated in a transparent resin, which is a poor thermal conductor. Nearly all heat produced is conducted through the back side of the chip. Heat is generated from the PN junction by electrical energy that was not converted to useful light, and conducted to outside ambience through a long and extensive path, from junction to solder point, solder point to board, and board to the heat sink and then to the atmosphere. The heat path of tungsten light bulbs is almost all straight into the atmosphere, starting from filament to the glass and ending with the thermal resistance from glass to the atmosphere. A typical LED side view and its thermal model are shown in the figures.

The thermal resistance between two points is defined as the ratio of the difference in temperature to the power dissipated; the unit is oC/W. From the LED junction to the thermal contact at the bottom of package, the thermal resistance is governed by the package design. It is referred to as the thermal resistance between junction and ambient (RJA). Different components in the heat conduction path can be modeled as different thermal resistances. The total power dissipated by the LED (PLED) is the product of the forward voltage and the forward current of the LED, which can be modeled as a current source. The ambient temperature is modeled as a voltage source. Therefore, the junction temperature (TJ) is the sum of the ambient temperature (TA) and the product of the thermal resistance from junction to ambient and the power dissipated. By “thermic Ohm’s Law”, we have the equation as follows: TJ = TA + (RJA × PLED) , and RJA = RJC + RCB + RTIM + RH

Intuitively, you can see that the junction temperature will be lower if the thermal impedance is smaller and likewise, with a lower ambient temperature. To maximize the useful ambient temperature range for a given power dissipation, the total thermal resistance from junction to ambient must be minimized. The values for the thermal resistance vary widely depending on the material or component supplier. For example, RJC will range from 2.6oC/W to 18oC/W, depending on the LED manufacturer. The thermal interface material’s (TIM) thermal resistance will also vary depending on the type of material selected. Common TIMs are epoxy, thermal grease, pressure sensitive adhesive and solder. In the most cases, power LEDs will be mounted on metal-core printed circuit boards (MCPCB), which will be attached to a heat sink. Heat flows from the LED junction through the MCPCB to the heat sink by way of conduction, and the heat sink diffuses heat to the ambient surroundings by convection. So, we can also add convection to the thermal model at the end of the heat transmission path. In the package design, the surface flatness and quality of each component, applied mounting pressure, contact area, the type of interface material and its thickness are all important parameters to thermal resistance design.

Passive thermal designs

Some considerations for passive thermal designs to ensure good thermal management for high power LED operation include:


Adhesive is commonly used to bond LED and board, and board and heat sinks. Using a thermal conductive adhesive can further optimize the thermal performance.

Heat sink

Heat sinks provide a path for heat from the LED source to outside medium. Heat sinks can dissipate power in three ways: conduction (heat transfer from one solid to another), convection (heat transfer from a solid to a moving fluid, for most LED applications the fluid will be air), or radiation (heat transfer from two bodies of different surface temperatures through electromagnetic waves).

Material – The thermal conductivity of the material that the heat sink is made from directly affects the dissipation efficiency through conduction. Normally this is aluminum, although copper may be used with an advantage for flat-sheet heat sinks. New materials include thermoplastics that are used when heat dissipation requirements are lower than normal or complex shape would be advantaged by injection molding, and natural graphite solutions which offer better thermal transfer than copper with a lower weight than aluminum plus the ability to be formed into complex 2 dimensional shapes. Graphite is considered an exotic cooling solution and does come at a higher production cost. Heat pipes may also be added to aluminum or copper heat sinks to reduce spreading resistance.

Shape – Thermal transfer takes place at the surface of the heat sink. Therefore, heat sinks should be designed to have a large surface area. This goal can be reached by using a large number of fine fins or by increasing the size of the heat sink itself.

Surface Finish – Thermal radiation of heat sinks is a function of surface finish, especially at higher temperatures. A painted surface will have a greater emissivity than a bright, unpainted one. The effect is most remarkable with flat-plate heat sinks, where about one-third of the heat is dissipated by radiation. Moreover, a perfectly flat contact area allows the use of a thinner layer of thermal compound, which will reduce the thermal resistance between the heat sink and LED source. On the other hand, anodizing or etching will also decrease the thermal resistance.

Mounting method- Heat-sink mountings with screws or springs are often better than regular clips, thermal conductive glue or sticky tape.

PCB (Printed Circuit Board)

MCPCB – MCPCB (Metal Core PCB) are those boards which incorporate a base metal material as heat spreader as an integral part of the circuit board. The metal core usually consists of aluminum alloy. Furthermore MCPCB can take advantage of incorporating a dielectric polymer layer with high thermal conductivity for lower thermal resistance.

Separation – Separating the LED drive circuitry from the LED board prevents the heat generated by the driver from raising the LED junction temperature.

Package type

Flip chip – The concept is similar to flip-chip in package configuration widely used in the silicon integrated circuit industry. Briefly speaking, the LED die is assembled face down on the sub-mount, which is usually silicon or ceramic, acting as the heat spreader and supporting substrate. The flip-chip joint can be eutectic, high-lead, lead-free solder or gold stub. The primary source of light comes from the back side of the LED chip, and there is usually a built-in reflective layer between the light emitter and the solder joints to reflect the light emitted downwards up. Several companies have adopted flip-chip packages for their high-power LED, achieving bout 60% reduction in the thermal resistance of the LED while keeping its thermal reliability.


LED Fabrication Roadmap Targets Packaged LED Prices of $2.20/klm by 2015

01 Jun

LED lighting is still not as aggressively priced as necessary to make it a viable option in the lighting market. The cost, currently at $18/klm, will need to make a significant drop by 2015 in order to meet market needs, writes PAULA DOE.

In the rush of news each week about new LED products, it’s easy to push aside the nagging issue that LED lighting still needs a drastic drop in cost if it’s going to become a serious volume market in the next few years.

Consensus input from the recent US Department of Energy solid-state-lighting manufacturing workshop was that last year’s aggressive roadmap for 10X cost reduction by 2020 wasn’t aggressive enough – the industry now needs to cut cost per lumen by 8X by 2015 to enable a viable volume LED lighting market that competes with fluorescents. That means current costs of about $18/klm need to drop to $2.20 klm, according to the preliminary figures. DOE will release the final version of its LED roadmap sometime this summer.

Best options to target for reducing these costs going forward are likely systems integration, metrology and test, and phosphors, concluded the gathered industry experts. Help is also coming from ongoing efforts to develop production equipment designed specifically for making LEDs, not ICs, and to develop some consensus on basic requirements for tools and materials so those from different suppliers work together.

DOE research funding has jump-started development of lower-cost projection lithography tools from Ultratech designed specifically to handle warped, transparent sapphire wafers; inspection tools from KLA-Tencor designed to map the micropits that cause LED defects; and pyrometers from Sandia National Labs and Veeco Instruments that can measure the critical temperature directly on the transparent wafer to better control the quality of epitaxial deposition.

Users and suppliers are also making progress towards consensus in SEMI standards committees on such basic issues as common placement of flats and notches for marking 6-inch sapphire wafers, and common cassettes and software and hardware interfaces to enable automation.

Progress on reducing the LED area-per-lumen

Recent improvements in making LEDs mean we’re probably already closer than most people think to a decent LED light bulb at an acceptable $10 price, argues Paul Scheidt, Cree LED Components product marketing manager. Key is the progress in continuing to reduce the active LED area required for the lumens, efficacy and thermal constraints of any particular application. He cites the trend towards multiple die arrays per package that reduce the cost of packaging and optics needed per die, allow balancing for consistent color, and provide a familiar one-die-per-fixture system that’s easy for users to integrate. Die on metal substrates allow users without reflow solder equipment to manually assemble systems by screwing die to heat sinks.

Matching each blue die to the right mix of phosphors can get consistent white light from the full distribution of die. And there’s another 100 lm/W of efficiency already achieved in the lab to be brought into mass production. “The highest lab efficiencies are ~230 lm/W, while commercial products are now running 130 to 140 lm/W,” says Scheidt. “That future improvement will allow use of a whole lot fewer LEDs.”

He notes that regulators’ labeling and testing requirements have done a good job at getting the products off the market that would disappoint consumers by not performing as advertised, and big box stores now have some low-cost bulbs of at least acceptable quality. “The quality is far better than anyone expected even a year ago,” he says. “The consumer market will happen faster than people expect. And cost will matter less once the industry develops and new styles become the driver. Look what happened with the thin LED TV.”

Simpler assembly of fewer parts per system

Another area key area of progress is simpler LED system design, with fewer, more integrated parts for easier assembly. One proposal for simplifying the system is Intematix’s remote phosphor, which combines the phosphor and the optics in one part. “We see more efficiencies coming from more integrated designs, and we think we’ll supply the phosphor and optics part of that, for fewer parts, and better thermal management,” says Intematix VP of development Chuck Edwards.

The commercial availability of remote phosphors allows easy matching of a consistent phosphor to the die, and moving the phosphor away from the die disperses the heat to improve reliability. Using a remote phosphor also simplifies the packaging problem down to just getting the blue light out as effectively as possible, providing more freedom to use simpler chip-on-board (COB) packaging. “Many general lighting solutions will move to COB arrays,” argues Edwards. “And with a dozen die for a 100W-equivalent bulb, averaging out wavelength over multiple die to one consistent average number for each array will be easy.”

First step was phosphors printed on plastic sheets that could also serve as diffusers for downlights. Now the company has introduced phosphors in injection-molded plastic domes, designed to sit on top of an array of blue LEDs on an aluminum heat sink, and to also distribute the light in the desired broadcast pattern, such as 270° for an A-19 bulb.

More brightness perhaps possible from quantum dots Progress on quantum dots may also help get more lumens out of LEDs, as this real potential application has spurred lots of recent work on scaling manufacture of these nanoparticles, and in developing practical solutions for printing or coating their polymer dispersions for lighting. These nanoscale particles can be tuned to emit a desired color with less lumen loss than phosphors, and can be mixed with fewer issues of differential degradation when used in remote geometry. “To mimic natural daylight, the penalty from phosphors can be 50%-60%,” argues Suresh Sunderrajan, president of NNCrystal.

Acuity Lighting and other suppliers are coating NNCrystal’s quantum dot solution on the secondary optics of their lamps to create the warm white light. Sunderrajan says NNCrystal’s particular technology reduces the typical re-absorption losses by separating the emission and absorption characteristics between the core and the shell, to be able to tune down the absorption to improve efficiency. The company says it has developed a stable, uniform, optically clear dispersion in polymer and a 3D precision coating process. The quantum dot materials are being manufactured in kilograms at its plant in China.

Intelligent lighting increases the value

With the maturing technology, users are also finding semiconductor-based lighting can do more than just provide light. Combine LEDs’ fast response and smooth dimming with some simple sensors and controls, and they can smartly adjust to deliver exactly the right amount of light in the right place at the right time, significantly reducing energy usage, without annoying people as current cruder systems are apt to do. Redwood Systems VP of building solutions Jeremy Steiglitz says users have seen ROIs in under two years from re-lighting projects that replace fluorescents with LEDs and sensors on a low-voltage DC network.

“Lighting is like a Trojan horse — it’s everywhere, in every room, and it’s on a grid,” he notes. “You couldn’t ask for a better place for a building’s eyes and ears.” And users are finding other uses for that network once it’s installed. One surprising application has turned out to be management of conference room space. The occupancy sensors can detect which rooms are in use, and by how many people, so users looking for an open conference room can find one, and facilities managers can track how many meeting rooms of what size the company’s workers need.


Osram Opto Delivers Small LED for Linear Lighting

01 Jun

Small Duris E 3 LEDs with wide beam pattern are optimized for linear and planar SSL applications where people don’t perceive the individual point light sources.

Osram Opto Semiconductors has announced a new sub-1W LED that specifically targets linear and planar lighting. The company intends for the Duris E 3 LEDs to be placed closely together in solid-state-lighting (SSL) luminaires and linear retrofit tubes so that people perceive a uniform source of light rather than individual point sources.

The target application is both LED-based retrofit tubes for T5 and T8 linear fluorescent tubes, and purpose-built SSL fixtures that will be used in place of fluorescent-tube troffers. Osram identified applications in open-floor-plan offices, production facilities, conference rooms, and warehouses as targets for the LEDs. The applications on that list share the need for uniform light, high energy efficiency, and relatively low procurement costs.

The Duris E 3 LEDs have a broad 120° beam angle and measure only 3×1.4 mm. Osram intends for the LEDs to be mounted closely together so that a person perceives “a single bright strip of light.”

“This new LED extends our portfolio in the low-power range and offers the usual high OSRAM quality,” said Andreas Vogler, Product Manager SSL at Osram Opto Semiconductors. “Bright LEDs are also recommended for smaller offices, shop lighting and signage.”

Osram will offer the new LEDs in a broad range of color temperature ranging from 3000K to 6500K. At 5000K the LEDs feature a CRI of 72 and deliver efficacy of 110 lm/W.

The company plans to follow the Duris E 3 with a larger and brighter LED later in the summer. The Duris E 5 will measure 5.6×3 mm.

Linear SSL trends

The trend toward purpose-built SSL-based linear fixtures is a strong one. Back in April, Cree announced the CR family of linear SSL fixtures was meant to replace tube-based fixtures.

At the recent Lightfair International (LFI) show, Cooper Lighting announced an LED module that was designed specifically for linear SSL fixtures. Moreover, the company has integrated the module into 32 different luminaires that carry different Cooper brands.

Osram Sylvania (a sibling business to Osram Opto) also launched a modular product at LFI that is meant for usage in 2- and 4-ft linear fixtures. The LED Distributed Array system combines 48 low-power LEDs on a 2×9-in circuit board. Luminaire designs can combine multiple modules to yield most any size fixture.

It’s not clear if the Sylvania module utilizes the Duris E 3 LEDs that were announced after LFI. But the LED Distributed Array press release issued at LFI makes familiar sounding claims saying the module offers uniform light with no hot or dark spots.

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