Regardless of the reality that light-emitting diode (LED) streetlights pose much tougher thermal-dissipation problems than do indoor applications, Taiwanese LED makers are competing to come up with LED streetlight solutions.

The reason: increasingly irrefutable proof of global-warming has pushed governments of economic powers worldwide to replace energy-guzzling streetlights in public work projects with power-efficient alternatives, notably LED types.



Globally, there are an estimated 120-130 million streetlights in service, with mainland China turning on some 15 million lamps and the United States, the second largest user, some 10 million, according to online clearinghouse LEDinside.

A study posted on the website points out that a high-power LED streetlight is 80% more energy efficient than a high-pressure sodium streetlight, and yet generates no toxic substances nor harmful rays. The research cautions that LED streetlights usually consume 50 to 300 watts, unavoidably giving off considerable heat while emitting huge amount of illumination. Thermal dissipation is, thus, the major hurdle in making LED streetlights practical. In fact, heat is major killer of high-power LED lamps.



Taiwanese LED insiders say profits on LED streetlamps are considerable, estimated at around NT$120 million (US$3.6 million) for every 10,000 systems, compared with NT$4,000 (US$121) for a traditional type. Such lucrative potential has even lured gigantic Taiwanese enterprise Hon Hai Precision Industry Co., Ltd. to jump onto the bandwagon.

"LED lighting products remain relatively expensive now whether for indoor or outdoor applications. But compared with individual consumers, governments have the purchasing power and are much more inclined to buy such costly lighting products," says H.N. Kuan, vice chairman of thermal-dissipation developer Thermoking Technology International Corp., which has recently applied its technology to LED streetlights.



His company has introduced 150-watt and 350-watt LED streetlamps employing a unique heat-dissipation technology. Kuan`s company developed the technology independently, paving the way for the firm to develop even larger lamps. "We started our LED lighting business with modest 150- and 350-watt models," Kuan explains, "because these high-power lamps pose a very high technological barrier to newcomers." With the technology it has developed so far, he says, his company will have no problem commercializing 1,000-watt lamps.

Thermal-dispersion Superconductivity

Kuan calls his company`s thermal-dissipation technology for LED streetlight "Thermal-Dispersion Superconductivity," which he claims is better than the heat-dissipation technologies used in 70- to 150-watt computer microprocessors. "This is particularly important to high-power LED lamps," he explains, because they have at least seven interfaces that produce heat, from LED dies to fans."



The technology, according to Kuan, limits temperature increase to just 0.079 degrees Celsius for each added watt, and to a maximum of only 22 degrees whatever the wattage. In competitors` products, Kuan claims, "The temperature increase is from 0.5 to 1.6 degrees for each added watt. That usually puts their high-power lamps in jeopardy, since they have no good heat-dissipation solutions."

Despite its relatively complicated design, Kuan`s thermal-dissipation module measures just 120mm x 140mm x 66mm and weighs only 850 grams. Achieving such compactness is due to Thermoking`s outstanding system integration capabilities, Kuan says, adding that counterparts using natural ventilation can be up to 15 times as large and yet "still deliver poor heat dissipation performance."

His "artificial cooling" is 15 times more effective than the "natural cooling" alternative, which he says is more suitable for low-power products.

Thermoking`s specially designed thermal fan, Kuan reports, comes with a guaranteed lifespan of 50,000 hours thanks to its IP65-grade dustproof and waterproof design. The LED module has a lighting fixture that boosts brightness efficiency to 95%, compared to what Kuan claims is an average of 80% for fixtures used by competitors.

Kuan reports that his thermal-dissipation technology is PCT patented, which is recognized by 128 member states.

The vice chairman says, "our business model is based on selling intellectual property. We`ll target public-works projects as our first market, followed by factories and households." Prices will drop to acceptable levels for household users, Kuan believes, only when the first two markets have grown to significant size. He once predicted that this would take five years for each market segment, but a flood of inquiries has prompted him to shorten the projection to just two years per segment. Among the company`s first noteworthy projects in this new segment was the installation of 350-watt lamps in the gymnasium of an elementary school near his company.

The company`s 350-watt street lamp has 192 one-watt LED chips and remains as bright as new even after 5,000 hours of continuous operation. "In theory our lamps have a maximum lifespan of over five years," Kuan comments, "although we sell them with only a two-year warranty."

The 150-watt lamp produces 5,000 lumens of brightness and the 350-watt lamp produces 12,000 lumens. Both are highly efficient, with the 150-watt model delivering 55 luxes of brightness to the ground from a height of 10 meters. "This is much better than the 10.7 to 21.4 luxes standard set by the Chinese National Standard (CNS)," Kuan insists," and it saves 60% of the electrical power consumed by 400-watt HID (high-intensity discharge) lamps."

Improving on Russian Space Technology

Advanced Thermal Devices Inc., another thermal-technology specialist in Taiwan, has built a patented thermal-dissipation module into 25W, 100W and 150W LED streetlights.

The company`s chief technology officer Dr. Sun Fu-sheng says the thermal technology was originally invented by the Soviet Union in 1982 for use in spacecrafts. His company worked with the National Taiwan University and Russian Academy Science in 2000 to tweak the spacecraft thermal technology, called loop heat pipe (LHP), so that it can be applied to LED streetlights. The revision has won some patents for thermal solutions for LED streetlights.

The structure of LHP is quite simple, comprising of a notebook-size aluminum plate with a closed pipe loop atop. Water inside the pipe acts as coolant and is pumped into the pipe by an "evaporator," which vaporizes the water as it picks up heat. The vapor then releases heat as it cools to ambient levels, and is condensed into water in the condenser. The water flows back to the evaporator through a connecting pipe, with the water carrying away heat in each loop.

The thermal-dissipation technology, according to Sun, can maintain maximum junction temperature of lamps at 60 degrees Celsius. The company has built the thermal module into LED streetlights giving off 60 lumens per watt.

"Our thermal module does away with cooling fans, making it light and compact," Sun says. The module weighs less than three kilograms.

Sun notes that the former Soviet Union developed the LHP as thermal-dissipation device in spacecrafts because the structure is unaffected by zero gravity and its heat- conduction distance is theoretically long.

LED streetlights equipped with Advanced Thermal`s LHP module are now working on National Taiwan University campus and Southern Taiwan Science Park. "We will apply the technology to other applications like personal computers," Sun concludes.

However, the module`s current unit price of around US$100 makes it cost-ineffective for some applications. "There is ample room for our cost to come down. So, we believe our module will be eventually more widely practical," Sun says.

Everlight Electronics Co., Ltd., currently Taiwan`s No.1 LED packager, has introduced high-power LED modules for use in streetlights. The modules are rated at 1250 lumens at two amps and 10 volts, and 9000 lumens at three amps and 50 volts.

The company`s streetlights have the merits of wide-ranging color temperature from 2,500K to 9,000K, compliance to IP65-grade dustproof and waterproof designs, and low operating temperature ranging from 20 degrees to 40 degrees Celsius. Also, its streetlights are designed for wide beam diffusion, from 100 to 130 degrees, offering broad coverage.

Chip-on-Board Packaging

For the high-power modules the company has worked out an efficient thermal-dissipation solution-chip-on-board (COB) packaging. Such methodology keeps temperature increase for each watt added under eight degrees Celsius, compared with 15 degrees for each watt added with older technologies.

High color rendering index (CRI), at 95%, is the company`s other advantage. "Our rivals can deliver 80% at best," reports Andrew Liang, a senior sales engineer at the company`s domestic sales department. The higher the index reading the closer the lit object looks to being naturally-lit. He ascribes the company`s high CRI mostly to its unique formula-applying phosphor powder to red and blue chips vs. applying the powder to only blue chips.

Everlight is reported to have received trial orders from General Electric (GE), which is the only one of the world`s top three lamp makers without in-house LED packaging capacity. The other two makers are Philips and Osram.

NeoPac Lighting Inc., a Taiwanese LED-packaging startup, has recently come up with a 135-watt LED streetlight module that gives off 5,000 lumens. The streetlight`s module contains eight chips when used with a total of 18 of the company`s patented NeoBulb lamps, with the temperature at the positive-negative electrode junction staying under 60 degrees Celsius and the ambient temperature of the emitter at about 25 degrees. Measuring 720mm long by 450mm wide by 205mm high, the module can be used with most standard outdoor lighting fixtures currently available. It has an Ingress Protection (IP) dust-proof rating and waterproof rating of 6 and 5, respectively.

The core of the module features an efficient thermal-dissipation technology called "heat pipe," which NeoPac claims can maintain the junction temperature of the positive and negative electrodes of LED chips within a narrow range.

The heat pipe is not a new concept in the PC industry, which uses it to dissipate heat from personal computers. However, Jeffery Chen, NeoPac`s president and CEO, stresses, "We`re the first LED packager to apply the concept to LED lamps, and to have succeeded in reducing the junction temperature."

NeoPac`s heat pipe consists of an aluminum tube surrounded by stacked aluminum heat-dissipation fins. The pipe measures 50mm to 120mm in length, making it adaptable to various kinds of lighting fixtures. The company mounts its patented NeoPac Emitter LED module onto a pipe with its own "system-in-a-package" technology to make its patented "light engine." Encased in a housing, the engine becomes a "NeoBulb" lamp which, the company says, is a universal platform for a variety of lighting applications.

Defying Haitz Law

Chen says that he plans to boost the efficiency of his company`s 135W streetlight to 75 lumens per watt next year, up from 37 lumens now, to bring total illumination to 10,000 lumens. "By doing that," Chen stresses, "we will defy the Haitz Law and boost total lumens without any restriction."

The law was established by Roland Haitz, a scientist now retired from Agilent Technology, who predicted in 2003 that based on the previous record-a doubling of illumination every 18 to 24 months-the lumens from a single LED would increase 20 fold while the price of the diode would fall to one-tenth of the 2003 level by 2013. "Our achievement has caught Mr. Haitz`s attention," Chen says, showing an e-mail from the scientist on his computer screen.

NeoPac has won at least 50 patents for its LED lighting technology. The company recently introduced the 75W, 2,500-lumen "Lotus Lantern" aimed at the huge mainland Chinese market, which is now being promoted as energy-efficient lighting in the build-up to the 2008 Olympic Games in Beijing.

"We`re revolutionizing the world of lighting," Chen claims. "With our technology, we are bridging the gap between the innovative and traditional lighting industries."

Its achievement has made NeoPac a topic of discussion at industry symposiums, both domestic and international. According to Chen, heavyweight LED-lamp manufacturers such as Philips have approached the company in search of partnership.
(by Ken Liu)