Michael R. Krames

High-power phosphor-converted light-emitting diodes based on III-Nitrides

Phosphor conversion of light-emitting diode light for white light sources and some monochrome applications requires particular phosphor properties and has to take into account specific issues if aimed at high-power output. Limitations and solutions will be discussed, giving special considerations to drive and temperature dependencies. Efficiencies of 32 lm/W for white with good color rendering at 4600 K and 35 lm/W for green (535 nm) have been demonstrated.

Performance of High Power Light Emitting Diodes in Display Illumination Applications

The performance of liquid crystal displays and micro display projection systems is for a large part determined by the lamps and illumination optics they are using. Traditionally, gas discharge lamps are used, but light-emitting diode lamps are gradually taking over because of their attractive characteristics. We will discuss how the transfer to light-emitting diodes in the various display architectures changes the key performance parameters, remaining technical challenges, and prospects for future improvement

Sixty Thousand Hour Light Output Reliability of AlGaInP Light Emitting Diodes

Both fixed current density and variable current density stress conditions are used to study light output degradation of (Al_xGa_1-x)_0.5In_0.5P light-emitting diodes (LEDs) as functions of LED stress current and LED stress time. Quantification of the resulting data indicates that (Al_xGa_1-x)_0.5In_0.5P LED degradation, D, is a linear function of current density, J, and a logarithmic function of stress time, t, for stress times as long as 60 000 hours in duration. For stress times long enough and current densities high enough to saturate any short-term effects (Al_xGa_1-x)_0.5In_0.5P LED degradation is therefore quantified by the empirical equation D=D₁+D₂J+(D₃+D₄J)ln(t), where D₁, D₂, D₃, and D₄ are independent of LED stress current and LED stress time. Within the limits of the data presented here, this equation is shown to accurately describe light output degradation of individual LED lamps, the average degradation behavior of individual LED wafers, and the average degradation behavior of a distribution of multiple LED wafers. The resulting expression may thus provide helpful guidance in quantifying the tradeoff between LED flux and LED degradation, both of which depend linearly on current density

Phosphor materials and combinations for illumination-grade white pcLEDs

Blue III-nitride based power LEDs have opened the way for Light Emitting Diodes to penetrate the illumination market. Most wanted seem to be warm white, high color rendering devices. Phosphor-converted LEDs, which meet these requirements, have been recently announced and sampled; they will be put into the context of possible other solutions and for the first time discussed in some detail.

Green phosphor-converted LED

Green phosphor-converted LEDs using a blue pump InGaN diodes have advantages over the direct green InGaN LED with regards to color stability with drive and/or temperature. Added manufacturing steps are outweighed by higher color yield, as a range of pump colors can be used without changing the final chromaticity. The conversion losses can be smaller than the decrease in wall-plug efficiency from blue towards green, which has been reported by many sources. A distinct disadvantage of the concept is due to only one color and phosphor proven - SrGa2S4:Eu2+ and 535 nm peak wavelength.

Performance and trends of high power light emitting diodes

We will discuss the performance, progress and trend of High Power Light Emitting Diodes (HP-LEDs), suitable for high luminance applications like micro-display projection, car headlamps, spot lamps, theatre lamps, etc. Key drivers for the high luminance applications are LED parameters such as internal quantum efficiency, extraction efficiency, drive current, operating temperature and optical coupling efficiency, which are important for most applications as they also enable higher lumen/

Phosphor-Converted High Power LEDs

ratios. Historical progress, prospects for improving these parameters and potential optical luminance enhancement methods to meet the demands for the various illumination applications are presented.

Status and prognosis for solid-state lighting technology

Phosphor converted Light Emitting Diodes (pcLED) have undergone many changes of design over the last 11 years. For advanced applications, however, besides other binning criteria a closely binned color point appears to be a major issue. Manufacturing yield is closely related to this point. Philips Lumileds Lighting (PLL) introduced very recently a new compact solid state color converter - Lumiramic - which allows much closer color control by selecting perfect matches between blue pump LEDs and previously characterized converter tiles in a pick-and-place process. Lumiramic phosphor technology utilizes a ceramic phosphor plate and PLLs new Thin Film Flip Chip (TFFC) technology. A first application in Automotive Forward Lighting and some of the design considerations are outlined in the paper

High-power truncated-inverted-pyramid (AlxGa1-x)0.5In0.5P light-emitting diodes

Sustained improvements in epitaxial materials, device design, and packaging have positioned light-emitting diodes (LEDs) as the solution for future lighting needs worldwide. State-of-the-art LED performance is reviewed along with discussion of challenges and future outlook.

Performance and application of high power ultraviolet AlGaInN light emitting diodes

High power light emitting diodes (LEDs) are of interest for many lighting applications. Flux improvements can be achieved by scaling conventional chips to larger dimensions. However this scaling results in a decrease in extraction efficiency. These penalties can be offset by modifying the chip geometry such that the number of internal reflections is reduced, thereby increasing the probability of photon escape. LEDs with a truncated-inverted-pyramid (TIP) geometry have been fabricated and packaged. Peak efficiencies exceeding 100 lm/W have been measured (100 mA dc, 300 K) for orange ((lambda) p approximately 610 m) devices. In the red wavelength regime ((lambda) p approximately 650 nm), peak external quantum efficiencies of 55% (100 mA dc, 300 K) have been achieved. Flux exceeding 65 lumens from a single 594 nm device has also been demonstrated. These characteristics match and/or exceed the performance of many conventional lighting sources.