In the increasingly popular world of light-emitting diodes (LEDs), an emitter’s light output per given input (efficiency), heat management, and small footprint are critical. So if you can make dramatic advancements in just one of these three areas, you’ve done a lot—especially in the hot flat-panel-display backlighting market.
But when you achieve industry-leading benchmarks in light output, temperature tolerance, and drive-current capability all at the same time, you’ve reached some significant milestones. That’s what Lumileds Lighting has achieved with its Luxeon K2 LEDs (Fig. 1). Its advanced package provides increased efficiency and simpler manufacturing for less cost.
“Luxeon K2 shatters every performance record in the power LED industry by a wide margin, and that has far-reaching implications for luminaire manufacturers and other lighting solution providers,” says David Eastley, product marketing manager for the K2 line. The lighting industry uses the term luminaire to define a lighting fixture or fitting. “With K2, we start a new chapter for solid-state lighting by simultaneously increasing the brightness threshold and simplifying the engineering required to use high-power LEDs.”
A white light output at a color temperature of 6500 K with 1500 mA of drive current and a forward voltage of 3.85 V produces 140 lm. This figure outstrips the output figure of other power LEDs on the market by 15% to 20% for an efficacy of 24 lm/W at a power dissipation of 5.8 W. At 700 mA of drive current, the white LED delivers 100 lm, which is equal to about 40 lm/W.
Key to this performance is the series’ novel packaging structure. With its efficient heat management, designers can drive the LEDs at industry-maximum junction temperatures of 185°C. Designers also can deliver more light in current applications with existing thermal designs, making it possible to reduce or even eliminate heatsink requirements. The result is a lower cost of system thermal design and the ability to produce applications in environments with severe heat conditions. The Luxeon K2 LEDs feature the lowest thermal resistance on the market at 9°C/W.
Another performance benchmark for the K2 family is moisture tolerance. The K2 line meets JEDEC Level 2a standards for moisture tolerance, which means the LEDs can withstand four weeks of factory floor life prior to preconditioning. Compare that with the JEDEC Level 4 ratings of other power LEDs, which feature only 72 hours of moisture resistance.
Unlike a traditional 5-mm indicator packaged LED, the Luxeon LED uses a different packaging and heat-management approach. In a traditional high-power LED, a small LED chip is mounted on a reflector cup on a leadframe. The entire device is encased in an epoxy for protection that also serves as the lens. This technique limits input power to less than 0.1 W and has high thermal resistance. In addition, its epoxy material can only handle temperatures up to 120°C.
In the Luxeon approach, a large LED chip is encapsulated in a soft inner gel, and then everything is encased in a plastic lens. A hexagonal slug heatsink of either copper or aluminum is located on the bottom of the package (Fig. 2). This configuration permits input power levels up to 1 W or more and reduces thermal resistance by more than an order of magnitude over conventionally packaged power LEDs. Input drive currents up to 1500 mA are possible.
The Luxeon family is available in a variety of colors, all of which feature high light outputs at a junction temperature of 185°C (Fig. 3). For red, orange, and amber colors, the LEDs use aluminum-indium-gallium-phosphide (AlIGaP) semiconductor materials. For green, blue, and white colors, indium-gallium-nitride (InGaN) materials are used.
While the company has yet to release pricing information on its K2 family, it expects pricing to be in line with previous-generation products that provide high price/performance ratios. For example, a white Luxeon III LED now costs $3.45 each for quantities of less than 10,000 units, delivering 23 lm per dollar. Luxeon I LED pricing is as low as $1.30 in low volumes.