Since 1995, the market for high-brightness LEDs has grown at an average annual rate of 58.4% to reach a value of 1.2 billion in 2000. This growth has been driven by the increasing performance of high-brightness LEDs across the visible spectrum, and the resulting development of new applications that previously could not be addressed with conventional, low-brightness LED materials. The next major challenge for the high-brightness LED industry will be to achieve significant penetration of the worldwide lighting market, which is estimated at $12 billion.

The light for the 21st century Japanese national project, which is based on the high-efficient ultraviolet (UV) light- emitting diode (LED) and phosphor systems, has started from 1998 in Japan. The proposal of UV white LED system for general lighting applications has for the first time in the world been done at August 1997 before start up the project. The outline and purpose of this project are introduced. This is also the brief summary of this national project based on white LEDs lighting, which has been carried out by the cooperation between universities and companies in the fiscal year 2000. In particular, we have demonstrated high- power UV LED having an external quantum efficiency of 24% at an emission wavelength of 382 nm. With increasing forward- bias current, the output power increased linearly and was estimated to be above 38 mW at 50 mA. Basic illumination properties of the lighting sources using phosphor-based UV white LEDs are described.

Everywhere in the world, the highest quality and quantity of lighting is required during the surgical operations. However, the surgical approach has had many types and various angles, common ceiling surgical halogen lighting system cannot provide an adequate amount of beams because the surgeons' heads hinder the illuminations from reaching the operation field. Here, we newly design surgical lighting system composed of white LEDs equipped on both sides of goggles, which controls the lighting beams to the gazing point. With this system, it is just needed for surgeons to wear light plastic goggles with high quality LEDs made by Nichia. In fact, we have succeeded in the first internal shunt operation in the left forearm using the surgical LED lighting system on 11th Sept 2000. The electrical power for the system was supplied from lithium-ion battery for 2 hours. Since the white LEDs used were composed of InGaN-blue-emitters and YAG-yellow-phosphors, the color rendering property was not sufficient in the reddish colors. Therefore, in the next approach, it is very important to develop the spectral distribution of white LED to render inherent color of raw flesh such as skin, blood, fat tissue and internal organs. To improve the color rendering in red colors, some adjustments should be given in the fluorescents layers. Design of goggle is also very important for cutting into the real practical market of white LEDs.

For widespread adoption in general-purpose illumination applications, light-emitting diodes (LEDs) must reliably produce a substantial amount of white light at a reasonable cost. While several white LED technologies appear capable of meeting the implicit technical requirements for illumination, their high purchase price (relative to traditional light sources) has heretofore impeded their market advancement. Binary complementary white (BCW) LED illuminators, first introduced commercially in late 1997, appear to offer great potential for addressing the commercial and technical demands of general-purpose illumination applications. Many properties of BCW LED systems derive from AlInGaP LED chips, the source of up to 80% of the luminous flux projected from BCW devices. This configuration yields a number of benefits, relative to other white LED approaches, including high luminous efficacy, low cost per lumen, and high luminous flux per discrete component. This document describes BCW illumination systems in detail, beginning with a review of generic LED attributes, basic illumination requirements and applied photometric and colorimetric techniques.

Over the past 5 years, the application of white LEDs for ambient lighting has been investigated in the remote villages of Nepal. Currently, lighting is often met using kerosene wick lamps, which emit unhealthy levels of fumes, or by burning sap-filled pine sticks, which are worse than the kerosene lamps. A team of students from Calgary University developed some LED lamps that could easily be fabricated in Nepal using local materials and personnel. To generate power, a pedal DC generator was developed to charge batteries, as well as a simple wind turbine. The Nepal Light Project implemented a series of many projects over the last 2 years in several villages across Nepal, using several different power generating systems. A total of 142 households, two schools and a temple were fitted with lamps in 2000, and more will follow in 2001. A research project has also been undertaken in Nepal for the Danish International Development Agency (DANIDA) to investigate the potential for energy efficient lamps in the micro hydro industry. The R&D project was very small, and conducted basic testing on locally available compact fluorescent lamps and LED lamps. The report concluded that encouraging the use of CFLs would decrease costs by 30-50%, and that they should be included in the subsidy policy, along with power factor correcting capacitors. LED lamps should not be overly encouraged as the development of the diodes was advancing very rapidly. The real advantage of LED lamps lies in extremely low maintenance costs due to the low power requirements and long life, which is just as important for remote villages as it is for traffic lights and exit signs. It is estimated that these low ongoing costs could be as low as $3/household/year for a rural lighting project. Pilot projects should be encouraged to demonstrate and investigate the potential of WLEDs for lighting in remote communities in developing countries. With 2 billion people without access to electricity, and lighting being the first end use people generally require, the potential for white LEDs is nothing short of staggering, but they will face challenges similar to CFL technology due to the high initial cost of the lamps.

Sandia assessed white LED lamps for parking lot, security and bike path lighting for the City of Albuquerque. Powering these lamps with photovoltaics was of particular interest to the city. Eight commercially available lamps were tested; one was AC and all others were 12-volt DC. Because DC-only photovoltaic systems do not regulate output voltage, a 12-volt nominal photovoltaic system can see a voltage range from 10.5-15.3 volts. Therefore, the LED lamp must be specified for the DC voltage range expected with a photovoltaic system. We found several failed lamps at the high voltage range of our test, which is below voltages that can be seen in the field. In addition, LED lamps need to be more powerful and cost competitive, and temperature and lifetime issues need to be addressed in order to be more widely useful with photovoltaic systems for illumination applications. We concluded that presently available white LED lighting powered by photovoltaics could be considered for bike path lighting applications where the area is remote, or for security lighting in areas that are difficult to access. We do not recommend LED lamps for much larger flux levels such as parking lot lighting at this time.

We fabricated the white light-emitting diodes without phosphor materials using phase-separated InGaN active layers. The white luminescence was attributed to the broad distributions of indium composition and size of quantum dot- like In-rich regions in the phase-separated InGaN Ternary alloys.

White light was obtained by mixing blue light from the emission of a GaN chip and a yellow light by the fluorescence of a Y₃Al₅O₁₂:Ce_0.05 yellow phosphor. A uniform coating of yellow phosphor on a GaN chip and an optimized thickness of a phosphor layer were necessary for achieving efficient white LED. Several methods for coating yellow phosphor particles such as the slurry method, the settling method, the electrophoretic deposition (EPD), and the modified EPD were examined for preparing the phosphor layer. The properties of the phosphor layer prepared by these methods were examined using SEM, XRD, and photoluminescence. The intensity of white light and the harmony between blue light and yellow light were dependent on the thickness of the phosphor layer. The properties of the phosphor layer made by the EPD such as packing density, thickness and uniformity could be more easily controlled than the slurry and settling methods. Further weak adhesion strength of phosphor particles by the EPD could be overcome via the use of a UV curable PVA+ADC layer on the phosphor layer in the EPD.

A combinatorial approach has been used to generate solid state thin-film of different garnet structures (A_1-xB_x)_3-z(C_1-y,D_y)₅O₁₂:Ce³⁺_z (called libraries), where A, B = Y, Gd, Lu, La; C, D = Al, Ga, Sc; x and y = 0 to 1.0; and z = 0.03. X-ray diffraction was used to select library samples of the crystalline garnet phase. Combinatorial chemistry methods were used as a tool to rapidly synthesize and screen potential inorganic phosphors for use as blue to yellow conversion phosphors in white LEDs. Libraries of these various garnets were then characterized spectroscopically. Emission and excitation trends are reported for various libraries and were found to reproduce previous trends in literature. Lattice constants, chromaticity, and PL intensity are also examined as a function of the different compositions. Emission and excitation trends reveal that as larger cations are substituted for the Y (dodecahedral) site in YAG, emission and excitation are red-shifted and as larger cations are substituted for the Al (octahedral and tetrahedral) site, emission and excitation are blue-shifted. If smaller ions are substituted for those respective sites an opposite trend is observed.

We optimized co-doped (Gd_2-x-yA_x)O₃:Eu³⁺_y phosphors for red FED phosphors using a combinatorial synthetic method and monitoring their photoluminescence and cathodoluminescence at low-voltage excitation. We have used a scanning multi-inkjet or adjustable micropipette delivery system and delivered micro- liter volumes of precursor solutions to the collection of each sample holders rapidly and accurately. Using combinational chemistry, we can at once characterize the UV, VUV, and CL properties of many individual compounds prepared in each sample holders. We find that Al co-doped Gd₂O₃:Eu³⁺ phosphors, i.e. (Gd_1.83Al_0.05)O₃:Eu³⁺_0.12 are superior to the commercial Y₂O₃:Eu phosphors at low-voltage excitation 400V. The filament lightbulbs and halogen lamps are widely used to light houses and offices but are energy-inefficient. GaN- based blue LEDs are the excitation source for YAG:Ce phosphors and the YAG:Ce phosphors convert the blue light into red and green lights. Using combinatorial chemistry, we find the optimal YAG:Ce phosphors, (Y_0.95Ce_0.05)₃Al₅O₁₂ for white LEDs. We fabricate highly energy-efficient white light emitting diodes by combining Yttrium Aluminium Garnet (YAG):Ce phosphors and blue LEDs.

A III-nitride blue LED structure based on the system of two wells with charge asymmetric resonance tunneling (CART), which allows enhancing the number of the electrons captured into the active region with the quantum well, was systematically studied. The barrier design uses the charge asymmetric resonance-tunneling phenomenon, which allows making the barrier transparent for electrons and blocking for holes. The growth and post-growth processes were optimized to achieve an efficient CART LED. The output power of 4 mW at the operating current of 20 mA has been achieved, corresponding to the external efficiency of 6%. Results presented in this report include the optimization of the quantum well growth parameters, bowing parameter for InGaN alloys grown on GaN, dry etching of III-nitride materials, Ohmic contacts to p- and n- type GaN, electrostatic discharge (ESD) problems related with the reliability of LEDs. The results presented include also modulation-technique LED characterization to tune the maximum radiative-recombination efficiency in accordance with the common operating current density.

Edge emitting LEDs(EELEDs) can be used to generate full color scanned displays. Conventional LEDs lack the high speed modulation characteristics and radiance required for this application. InGaN-based EELEDs can be used for blue and green sources, and InGaP-based EELEDs for red sources. These semiconductor light sources are processed and packaged similar to laser diodes, but the primary source of output radiation is spontaneous emission. In this paper we describe the optical farfield characteristics of EELEDs, as well as their near-field and imaging properties. Comparisons are made to laser diode (LD) sources. The near- fields and far-fields of these devices have characteristics in common with both laser diode and conventional surface emitting LEDs. Smaller emitter dimensions produce laser- diode-like diffraction limited behavior, while larger emitter dimensions supporting higher order optical modes, produce broad far-field intensity distributions, and geometrical imaging characteristics. Partly due to the absence of optical gain, the wall plug efficiencies, and optical power levels, are also much lower than laser diodes.

Computer modeling of distributive light pipe systems using light emitting diode (LED) sources to produce uniform illumination for liquid crystal displays (LCDs) is presented. Due to their small size, lower power consumption, and lower heat generation, LEDs are a natural source choice for display illumination. However, to be useful in display applications, LEDs must be made to produce uniform illumination over the display area. The conversion of an LED's output flux distribution to one that is uniform over a given area can be accomplished with plastic, injection-molded light pipes. Illustrative examples of LED light pipe display systems are presented. These systems compare output coupling surface geometry for two LED input coupling scenarios; direct and indirect input coupling. Computer modeling via commercial software packages is used to optimize and analyze system designs. It is critical in these simulations to have accurate source models. Therefore close attention is paid to the LED source model. The final simulation results are presented and uniformity and total light output is compared. The implications of these results for display applications are discussed.

At the current time most of the attention in the solid-state lighting field has been placed on the blue and white light emitting diodes (LEDs). It has and will continue to be extremely important to concentrate on increasing the efficiencies of these devices. However, one of the most overlooked benefits of LEDs is that they are intrinsically simple to control. In this paper, the authors will discuss a technology that is currently being developed to enable fixtures incorporating LED light engines to be connected to a digital lighting network. A description of such a network enabling device and the results from a technology demonstration of a prototype system are provided.

The rapid development of high-brightness light emitting diodes (LEDs) has made this technology a potential candidate for architectural lighting applications. There are two distinct approaches for creating white light. The first is combining blue LEDs with a phosphor and the second is mixing monochromatic LEDs in appropriate proportions. This manuscript presents some of the critical issues involved in creating a good quality, stable white light source using the color mixture approach for LEDs. Some sample calculations for mixing different colored LEDs to obtain specific color appearance (CCT) and color rendering properties (CRI) are shown in this paper. Calculations show that the CRI values of mixed-color white LEDs can be changed significantly by shifting the wavelengths of the LEDs by a small amount. It is also shown that small amplitude and wavelength shifts can cause perceivable color differences in the mixed-color white LEDs. Therefore, circuits must be properly designed to power these types of white light sources so that they are acceptable for architectural lighting applications. Because the light output variation as a function of time at different drive currents was not readily available, an experiment was conducted to quantify the light output change as a function of time for red, green, blue and white 5-mm LEDs, at fiber different constant current values (20,30,40,50 and 50 mA). The light output of the different colored LEDs depreciated at different rates. The depreciation rates increased in the following order: red, green, blue, and white. Furthermore, the light output depreciation increased with increasing drive current. The red LEDs has the least amount of light output depreciation rate variation as function of drive current, green and blue LEDs ranked after that, and white LEDs had the most variation for the same drive current variation. A group of twelve new high-powered phosphor-based white LEDs were tested at their rated current, (which is much higher than 20 mA), and their light output depreciation rate was very much less compared to the 5-mm phosphor-based white LEDs operating at 20 mA. It appears that manufacturers have solved the excessive lumen depreciation issues faced by traditional white LEDs by packaging them differently and properly extracting the heat, and by using materials that do not degrade over time. This progress makes the LED technology a more promising candidate for architectural lighting applications.

Polychromatic solid-state lamps that produce white light by additive mixing of the emissions from primary colored light emitting diodes (LEDs) should have a higher luminous efficiency that those using phosphors. These lamps require emission spectra that feature an optimal trade-off between luminous efficacy and color rendering. We developed a mathematical technique that allows us to maximize the luminous efficacy and general color rendering index (CRI) for the white solid-state lamp composed of an arbitrary number of primary LEDs with given spectra. We use this method in order to compare the optimal efficacy and general CRI for 4 and 5 primary LEDs with that for 2 and 3 LEDs. For a particular color temperature, the required number of primary LEDs depends on the trade-off between efficacy and general CRI. The quadrichromatic lamp is shown to meet requirements for most practical applications. Quintichromatic lamps and lamps with a higher number of primary LEDs yield negligible benefit in improving color rendering. However, quintichromatic LED lamps are capable of producing quasi-continuous spectra that might meet special lighting needs.

The first internal shunt operation in the left forearm has successfully been performed using the surgical lighting goggle composed of InGaN-yttrium aluminum garnet (YAG)-based white light emitting diode(LED) arrays. This system supplies a total luminous flux of about 200 lumen for several hours by driving with rechargeable Li-ion batteries. Further increase in luminous flux can be achieved by both the progress of emission efficiency of white LEDs and the development of dense packaging technique of LED chips. Moreover, the color rendering properties of white LEDs are inferior to the standard illuminant especially in violet, green and red spectral range. In this paper, several device structures are proposed for achieving power lighting and for higher color rendering properties. The key technology for power lighting is how to radiate the heat out of LED chips, and that for higher color rendering is how to add desired illumination-spectral-components to LEDs according to the application fields.

InGaN/GaN multiple-quantum well (MQW) light-emitting diode (LED) was fabricated using a SiO₂ current blocking layer (CBL) inserted underneath the p-pad electrode. The forward voltage, V_f at 20 mA for InGaN/GaN MQW LED with a CBL(V_F=3.5 V) was slightly higher than that of the conventional InGaN/GaN MQW LED(V_F=3.4V) due to the reduction in the total area of p-type metal contact between the transparent Pt layer and the p-GaN. However, the light- output power for InGaN/GaN MQW LED with a CBL at 20 mA was significantly increased by 62% compared to that for the conventional InGaN/GaN MQW LED structure. This increase in the light-output power can be attributed to the more amount of current injected into the active area of the LED through the light-transmitting metal layer and a reduced parasitic optical absorption in the p-pad electrode.

Electrophoretic deposition was employed to apply a phosphor coating, for use in the fabrication of a full color screen consisting of red (R), green (G), and blue (B) phosphors. Patterned phosphor layers can be fabricated by the electrophoretic deposition, combined with photolithography. For this process, R,G, and B phosphors were deposited on a patterned ITO glass by means of photoresist. The phosphor could be deposited, not on the photoresist surface, but on the patterned conductive substrate, since the photoresist has insulating properties. Conventional photolithographic conditions cannot be used for electrophoretic deposition due to the fact that the photoresist is soluble in the alcoholic solvent, which is used after baking. A suspension of the insoluble photoresist was obtained by optimizing the baking temperature. Patterned color screens, prepared by electrophoretic deposition combined with photolithography were studied using SEM and photo luminescence spectroscopy.