This article will overview the XLamp LED family and discuss the key features and applications of Xlamp products. Lighting applications featuring XLamp LEDs maximize light output and increase design flexibility, while minimizing environmental impact due to less landfill waste and hazardous materials such as mercury.
1. High Power vs. Standard LEDs
In comparison to Standard LEDs, High power LEDs operate at higher currents - more than ten fold compared to standard LEDs – and emit more light and consequently glow brighter. The increased power required to produce this light has the effect of also producing more heat. The definition of a Power LED is one that operates at greater or equal to 1W. In contrast Standard LEDs consume less power and produce less heat. However, despite the increased heat exhibited by High Power LEDs, their heat dissipation design is better due to comparatively lower junction temperature, enabling a longer life span.
2. Basic Advantages of LED Light
Lighting-class LEDs can now deliver the brightness, efficiency, lifetime, improved color temperature range, and white-point stability required for general illumination. Lighting-class LEDs offer efficient, directional light that lasts at least 50,000 hours. LED operational lifetime is not affected by shock or vibration damage. Shocks and vibration shorten the lifespan of a traditional light bulb. LED light sources give better light-beam uniformity than conventional light sources and simplify optical-system design.
3. Overview of XLamp LEDs
CREE leads the industry in brightness and reliability for power LEDs with its XLamp LED family. Through XLamp LEDs, CREE is enabling the lighting industry with efficient, environmentally friendly LED light. XLamp LEDs lead the solid-state lighting industry in brightness while providing a reflow-solderable design that is optimized for ease of use and thermal management. An XLamp LED combines an LED chip, electrical and thermal connections, encapsulating substances, an optical element, and a phosphor system (Figure 1).
Figure 1: XLamp LED
XLamp family includes royal blue, blue, green, amber, cyan, red-orange, red, cool white, and warm white LEDs. Mixing these colors enables the creation of any color in the visible spectrum. The lighting industry demands both high lumen maintenance and very stable color output from the incumbent lighting technologies. White high-power LEDs will experience shifts in white light output over their operational life. High-temperature conditions will accelerate these white point shifts. Therefore, Cree monitors the white light output of the XLamp LED over time under high-temperature conditions. XLamp offers 50 times the life of a typical incandescent bulb and 5 times the lifetime of an average compact fluorescent lamp. In fact, if you ran one Cree lamp for 6 hours per day every day, it would last for nearly 23 years. Thermal path between the LED junction and ambient conditions affect junction temperature which will cause light output reduction and accelerated chip degradation. XLamp LED packages uses a substrate with an extremely low thermal resistance in order to efficiently channel heat away from the LED junction and into the thermal path. The main purpose of secondary optics is to change the light output pattern of the LED. The chart of figure 2 illustrates the luminous intensity performance to beam angle of the different XLamp LEDs.
Figure 2: Relative luminous intensity as funciont of beam angle for different XLamp LEDs
4. XLamp LED Thermal Management
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. The heat sink diffuses heat to the ambient surroundings by convection. In heat management design, designers must know what junction temperature they are operating at, and whether the product will reach the maximum value or not. If the designers can keep the junction temperature low, they will achieve longer life for the LEDs. Based on internal long-term reliability testing and standardized forecasting methods, XLamp LEDs will maintain an average of 70% lumen maintenance after 50,000 hours, provided the LED junction temperature is maintained at or below 80°Celsius.
5. XLamp Part Number
All XLamp LEDs are tested and sorted by color and brightness into a unique bin. Each bin contains LEDs from only one color and brightness group and is uniquely identified by a bin code. White XLamp LEDs are sorted by chromaticity (color) and luminous flux (brightness). Color XLamp LEDs are sorted by dominant wavelength (color) and luminous flux (brightness), or in the case of royal blue, radiant flux (brightness). Amber, red-orange and red LEDs are additionally binned into forward voltage bins. Kits contain LEDs from a number of similar bins and are fully defined by their part number.
6. Design Process for Lighting Applications
Firstly, the design goals should be based either on an existing lighting performance or on the application’s lighting requirements. Then, the designer should specify any other goals that will influence the design, such as special optical requirements or being able to withstand high temperatures. Design goals will place constraints on the optical, thermal and electrical systems. Good estimations of efficiencies of each system can be based on these constraints. The combination of lighting goals and system efficiencies will drive the number of LEDs needed in the application. Once the design decisions have been made, the final steps are to build and evaluate a prototype luminaire.