|XLamp 3 in white|
The 3-watt Xlamp measures 70 x 90 mm and operates at a forward current of 700 mA. A full range of colors, including cool white, are available. Hiller says that Cree demonstrated warm white devices in the 2800-3550 K range at Lightfair in April. "We are sampling customers with both 1- and 3-watt warm-white devices but these are not really in high demand at the moment," he says.
The luminous flux values compare very favorably with competing devices in the market. For example, at a forward current of 700 mA, the white Luxeon III Lambertian emitter from Lumileds has a minimum flux of 60 lm and a typical value of 65 lm, according to the datasheet. The typical flux is 80 lm at 1000 mA.
The one-watt white XLamp is rated at 45 lm, roughly half the new 3-watt version, but Hiller says that the 3-watt product is less than twice the price of the one-watt (obviously pricing is strongly dependent on volume). This means that the "dollars per lumen" figure for the 3-watt XLamp represents an improvement over the one-watt product.
"Pricing depends on volume but using list pricing the XLamp 3 7090 provides at least a 20 percent increase in lumens per dollar," says Hiller. "Our customers are telling us that Cree offers a very competitive price point in terms of dollars per lumen."
Cree says that it has seen "significant market demand" for a 3-watt product, although one-watt devices are running in much higher volumes at the moment. For some special applications, such as flashlights, there is demand for the extra luminous flux provided by three-watt devices.
In fact, Cree has already announced its first design for the white XLamp 3, which will be incorporated into Cyberlux's new RelyOn portable work and emergency light. "Based on the new 3-watt XLamp LED, Cyberlux's new RelyOn portable emergency light achieves more than 60 hours of operational spot and flood lighting," said Mark Schmidt, Cyberlux president and COO. "Cyberlux is developing a broad range of products based on Cree's XLamp LEDs for emergency, task and large scale lighting applications."
Hiller says that Cree has no immediate plans to develop higher-power devices. "Other companies are offering 5W devices and above, but at this point we don't see the demand. We are heavily market driven, so we won't announce a new product unless there is market pull-through."
The XLamp package, which is reflow solderable, has a thermal resistance from the LED junction to the solder point of 17 °C/W. A low value of thermal resistance is vitally important for maintaining a low junction temperature within the LED chip. Equally, the end product must be designed so that the thermal resistance from the solder point to ambient is kept to a minimum.
The XLamp has an electrically neutral thermal path, which means that the anode and the cathode are separate both from each other and from the area which is used to connect the package to the PCB. This provides more freedom in the design of the electrical circuits to drive the LEDs and also the choice of materials.
Hiller says that Cree is not quoting mean-time-to-failure (MTTF) data at the moment. "We are currently performing various standard and long-term life tests," he says, "and we are preparing an application note which will cover both 1- and 3-watt devices."