This PDF file contains the front matter associated with SPIE Proceedings Volume 9003, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

The scope of the present paper is the derivation of a merit function which predicts the visual perception of LED spot lights. The color uniformity level Usl is described by a linear regression function of the spatial color distribution in the far field. Hereby, the function is derived from four basic functions. They describe the color uniformity of spot lights through different features. The result is a reliable prediction for the perceived color uniformity in spot lights. A human factor experiment was performed to evaluate the visual preferences for colors and patterns. A perceived rank order was derived from the subjects’ answers and compared with the four basic functions. The correlation between the perceived rank order and the basic functions was calculated resulting in the definition of the merit function U_sl. The application of this function is shown by a comparison of visual evaluations and measurements of LED retrofit spot lamps. The results enable a prediction of color uniformity levels of simulations and measurements concerning the visual perception. The function provides a possibility to evaluate the far field of spot lights without individual subjective judgment.

An innovative way of modeling dual-phosphors-converted white mid-power LEDs is established and demonstrated. We use near-field chromatic luminance measurement data to select ray tracing modeling parameters in LightTools and propose some key parameters to predict characteristics of LEDs accurately. Based on our model, we can precisely predict the change in efficacy and in correlated colour temperature of embedding LEDs in optical materials.

We have developed phosphor-free InGaN/GaN/AlGaN dot-in-a-wire core-shell white light emitting diodes, which can break the carrier injection efficiency bottleneck of conventional nanowire white light emitting diodes, leading to a dramatic enhancement of the output power. Additionally, such phosphor-free nanowire white light emitting diodes can deliver a very high color rendering index (CRI) of ~92-98.

We report on the development of a temperature-dependent electroluminescence experimental setup for characterizing the internal quantum efficiency (IQE) of high-brightness GaN-based light-emitting diodes (LEDs). A systematic IQE study of commercial LED chips from major LED manufacturers (including Cree, Nichia, Osram, and Sanan) is presented. The chips show distinctive temperature- and current-dependence in the IQE behavior. Analysis to correlate the onset of droop with the onset of high injection is also presented.

A GaN layer of 20 μm thickness grown by the liquid-phase epitaxy on c-plane sapphire was used as a template for the growth of blue light-emitting diodes (LEDs) with emission peak wavelengths of about 450 nm. As the underlying layer of the active region, an InGaN/GaN superlattice or two pairs of 100 nm undoped GaN and 20 nm GaN:Si layers on an n-type GaN:Si layer was found to be effective for reducing the forward voltage. By optimizing the multiple-quantumwell structure, LEDs having a 2.5-nm-thick InGaN well and 5-nm-thick GaN barrier exhibited the highest internal quantum efficiency (IQE) at both low and high currents. This IQE was much higher than that of LEDs on a sapphire substrate. The IQE of LEDs using the liquid-phase GaN grown on sapphire substrate exceeded more than 75% at a forward current density of over 200 A/cm².

We use thinner-quantum well to improve the droop behavior of GaN-base light emitting diode in simulation. Taking the advantage of that the thin quantum well will saturate easily, this characteristic of thin well will improve carrier distribution. Furthermore, this structure has more wave-function overlap than that of the thick well. This simulation result showed that decreasing the well thickness in specific position will not only improve the holes transport but also increase the quantum efficiency at high current density in the active region, and the efficiency droop behavior can be effectively suppressed. In this research, we designed three thin well structures by inserting different numbers of thin wells in the active region. We have compared them to the conventional LEDs, for which, the well thickness of 2.5 nm is used. The thin well structures have better droop behavior than conventional LED.

Green (λ~540 nm) - and red-emitting (λ~610 nm) InGaN/GaN disks-in-nanowires have been grown by RF plasma-assisted molecular beam epitaxy on (001) Silicon substrates. The growth of disks-in-nanowires heterostructures has been optimized and the nanowires have been passivated to achieve radiative efficiencies of 54% and 52% in the green and red InGaN disks, respectively. Radiative efficiency increases significantly (by ~10%) when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. Light emitting diodes on silicon, incorporating InGaN/GaN quantum disks as the active medium have been fabricated and the devices have been characterized. Quantum Confined Stark Effect (QCSE) blue-shift of 7nm and 15nm have been observed in the measured electroluminescence peak of the green and red LEDs respectively, from which polarization fields have been calculated in the disks to be 605kV/cm for green and 1.26MV/cm for red. For green and red LEDs, external quantum efficiency peaks at current densities of ~25A/cm² and 12A/cm², respectively. To improve light extraction efficiency, LED heterostructures have been transferred to Ag mirrors from the silicon growth substrate and preliminary device results have been demonstrated.

To obtain high light output power and high phosphor conversion efficiency of the white light-emitting diodes (WLEDs), various methods including the reflectors and the surface roughness technique were intensively investigated. The improvement results of the relating researches about the reflectors and the surface roughness technique employed in the LEDs were discussed in this article. The light output power of the resulting LEDs with ZnO nanorod diffused reflectors improved 56.6% compared with the conventional LEDs. The LEDs with ZnO nanorod antireflection layer obviously enhanced the light extraction performance. Furthermore, the flip-chip white LEDs (FCWLEDs) with the diffused ZnO nanorod reflector and ZnO nanorod antireflection layer were also proposed in this article. The output power and phosphor conversion efficiency of FCWLEDs with diffused ZnO nanorod reflectors and ZnO nanorod arrays antireflection layer were improved to 23.91 mW and 80.1% compared with FCWLEDs with flat reflectors. These results verified that the both of the diffused ZnO nanorod reflector and the ZnO nanorod array antireflection layer could effectively guide more blue light to improve the light output power and the phosphor conversion efficiency of resulting LEDs.

We present our latest results on developments of infrared and red light emitting diodes. Both chiptypes are based on the Thinfilm technology. For infrared the brightness has been raised by 25% with respect to former products in a package with standard silicon casting, corresponding to a brightness increase of 33% for the bare chip. In a lab package a wallplug efficiency of more than 72% at a wavelength of 850nm could be reached. For red InGaAlP LEDs we could demonstrate a light output in excess of 200lm/W and a brightness of 133lm at a typical operating current of 350mA.

LED luminaires are already beyond retrofit systems, which are limited in heat dissipation due to the old fitting standards. Actual LED luminaries are based on new LED packages and modules. Heat dissipation through the first and second level interconnect is a key issue for a successful LED package. Therefore the impact of known bonding technologies as gluing and soldering and new technologies like sintering and transient liquid phase soldering were analyzed and compared. A realized hermetic high power LED package will be shown as example. The used new techniques result in a module extremely stable against further assembly processes and harsh operating conditions.

High performance of GaN light-emitting diodes with a finger-type embedded contact (F-LEDs) was demonstrated on a Cu substrate for improved thermal management and increased efficiency. In contrast to common sapphire-based LEDs (C-LEDs) and the wing-type embedded LEDs (W-LEDs), the use of the finger-type embedded contact not only reduces the effect of the current crowding of W-LEDs to achieve a uniform current injection but also eliminates the problem of light shading of C-LEDs to obtain more output power. At 350 mA, the output power of the three LEDs was measured to be 329.39, 284.52, and 236.38 mW for the C-LED, W-LED, and F-LED, respectively; representing that the F-LED in output intensity was raised 39.3% and 20.3% higher than that in the C-LED and the W-LED. Similarly, a 63.61% increase of output power of F-LED was obtained as compared to the C-LED case at 700 mA current injection. At this point, the efficiency droop of F-LED is 33.7%, which is lower than that of 44.1% and 53.5% in W-LED and C-LED, respectively; results are promising for the development of high performance LEDs using the finger-type embedded contact.

A theoretical investigation of AlGaN UV-LED with band engineering of hole and electron blocking layers (HBL and EBL, respectively) was conducted with an aim to improve injection efficiency and reduce efficiency droop in the UV LEDs. The analysis is based on energy band diagrams, carrier distribution and recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates) in the quantum well, under equilibrium and forward bias conditions. Electron blocking layer is based on Al_aGa_1-aN / Al_{b → c}Ga_{1-b → 1-c}N / Al_dGa_1-dN, where a < d < b < c. A graded layer sandwiched between large bandgap AlGaN materials was found to be effective in simultaneously blocking electrons and providing polarization field enhanced carrier injection. The graded interlayer reduces polarization induced band bending and mitigates the related drawback of impediment of holes injection. Similarly on the n-side, the Al_{x → y}Ga_{1-x → 1-y}N / Al_zGa_1-zN (x < z < y) barrier acts as a hole blocking layer. The reduced carrier leakage and enhanced carrier density in the active region results in significant improvement in radiative recombination rate compared to a structure with the conventional rectangular EBL layers. The improvement in device performance comes from meticulously designing the hole and electron blocking layers to increase carrier injection efficiency. The quantum well based UV-LED was designed to emit at 280nm, which is an effective wavelength for water disinfection application.

Strain-compensated type-II InGaN-ZnGeN₂-AlGaN quantum wells (QWs) are studied as improved active regions for light-emitting diodes (LEDs). Both the band gap and the lattice parameters of ZnGeN2 are very close to those of GaN. The recently predicted large band offset between GaN and ZnGeN₂ allows the formation of a type-II heterostructure. The deep confinement of holes in the ZnGeN2 layer allows the use of a low In-content InGaN QW to extend the emission wavelength into the green wavelength region. A thin layer of AlGaN surrounding the QW is used as a strain compensation layer. Simulation studies of the proposed type-II QW indicate an enhancement of 5.6-6.8 times the spontaneous emission rate compared to InGaN-GaN QWs emitting in the green wavelength region.

We discuss the unambiguous detection of Auger electrons by electron emission (EE) spectroscopy from a cesiated InGaN/GaN light-emitting diode (LED) under electrical injection. Electron emission spectra were measured as a function of the current injected in the device. The appearance of high-energy electron peaks simultaneously with the droop in LED efficiency shows that hot carriers are being generated in the active region (InGaN quantum wells) by an Auger process. A linear correlation was measured between the high energy emitted electron current and the “droop current” - the missing component of the injected current for light emission. We conclude that the droop originates from the onset of Auger processes. We compare such a direct identification of the droop mechanism with other identifications, most of them indirect and based on the many-parameter modeling of the dependence of the external quantum efficiency on the carrier injection.

Auger recombination is at the hearth of the debate on droop, the decline of the internal quantum efficiency at high injection levels. The theory of Auger recombination in quantum wells is reviewed. The proposed microscopic model is based on a full-Brillouin-zone description of the electronic structure obtained by nonlocal empirical pseudopotential calculations and the linear combination of bulk bands. The lack of momentum conservation along the confining direction in InGaN/GaN quantum wells enhances direct (i.e. phononless) Auger transitions, leading to Auger coefficients in the range of those predicted for phonon-dressed processes in bulk InGaN.

Fully microscopic models for the calculation of the carrier dynamics and resulting optical response are used to investigate the validity of various models that have been suggested as the cause for the efficiency droop in GaN-based devices. Models based on internal piezoelectric electric fields, carrier localization, Auger and density-activated defect recombination are analysed. In particular, the models are used to simulate aspects of a recent experiment in which green emitting quantum wells were pumped resonantly and emission from adjacent ultra-violet emitting wells was attributed to carrier redistributions due to Auger processes. It is shown that the UV emission can be explained as a direct result of the optical excitation without involving Auger processes.

Soraa has developed a novel ammonothermal approach for growth of high quality, true bulk GaN crystals at a greatly reduced cost. Soraa’s patented approach, known as SCoRA (Scalable Compact Rapid Ammonothermal) utilizes internal heating to circumvent the material-property limitations of conventional ammonothermal reactors. The SCoRA reactor has capability for temperatures and pressures greater than 650 °C and 500 MPa, respectively, enabling higher growth rates than conventional ammonothermal techniques, yet is less expensive and more scalable than conventional autoclaves fabricated from nickel-based superalloys. SCoRA GaN growth has been performed on c-plane and m-plane seed crystals with diameters between 5 mm and 2" to thicknesses of 0.5-4 mm. The highest growth rates are greater than 40 μm/h and rates in the 10-30 μm/h range are routinely observed. These values are significantly larger than those achieved by conventional ammonothermal GaN growth and are sufficient for a cost-effective manufacturing process. Two-inch diameter, crack-free, free-standing, n-type bulk GaN crystals have been grown. The crystals have been characterized by a range of techniques, including x-ray diffraction rocking-curve (XRC) analysis, optical microscopy, cathodoluminescence (CL), optical spectroscopy, and capacitance-voltage measurements. The crystallinity of the grown crystals is very good, with FWHM values of 15-80 arc-sec and average dislocation densities below 5 x 10⁵ cm^-2.

A high current density over 1000 A/cm² operation in small chip size m-plane GaN-LED has been successfully demonstrated. The LED with chip size 450 × 450 μm² has emitted 1353 mW in light output power and 39.2% in external quantum efficiency (EQE) at 1000 A/cm² (1134 mA). The m-plane GaN-LED has showed asymmetric radiation characteristics. The radiation patterns are controlled by the surface of LED package, the height of LED chip, and striped texture on top m-plane surface.

An LED solar simulator containing LEDs emitting at 23 different wavelengths is described. Taking into account the natural spectral width of each of the LED wavelengths, a reasonably well-behaved and spike-free spectral continuum is demonstrated. The LED light source is based on a modular design that facilitates fabrication of arbitrarily large area simulators for both single solar cell and multi-cell module test and evaluation. The spectral tunability of this simulator makes it an attractive instrument for use in evaluating the performance of both conventional solar cells and tandem solar cells. The basic modular building block is a 10 cm x 10 cm “tile” consisting of the LED emitter platform with reflecting side mirrors and driver electronics conveniently located directly underneath the emitter platform in a compact yet flexible configuration. Combinations of tiles facilitate manufacture of solar simulators of arbitrarily large size and shape, with the advantages of high reliability, spectral tunability, lighter weight, no water cooling requirements and absence of high voltages. Excellent spectral mixing and intensity uniformity is obtained on the measurement plane, resulting in a simulator that meets Class AAA specifications according to ASTM and IEC standards.

The coherence length of electromagnetic waves created by different light sources is a largely overlooked parameter. Since the coherence length and its spectral distribution are essential for the entire field of interference, ranging from unintended destructive and constructive pattern to intended interference determining the nature of structural colors. We studied the spectral emission behaviour of GaN- and AlGaInP-based Light-Emitting-Diodes (LED) under thermodynamic equilibrium conditions driven by direct current as well as by short current pulses (500 ns) in the temperature range from 4.2 to 390 Kelvin. The coherence length under the different driving conditions was measured via a Fabry-Perot interference setup. We discuss the validity and limitations of the conventional determination method from the emission linewidth and lineshape. Besides the distinct shifts of the emission wavelength accompanied by significant changes of the full width at half maximum, we found quite high values for the coherence length exceeding 0.15 millimeters for the blue emission and 0.4 millimeters for the red emission at room temperature, respectively. Furthermore this contribution will also discuss the nature and interrelationships of coherence length, emission peak wavelength and the spectral distribution (lineshape and linewidth) of the investigated LEDs.

Illuminant metameric failure is frequently experienced when viewing material samples under LED generated light vs. traditional incandescent light. LED light temperatures can be improved with phosphor coatings, but long-wave red light is still generally absent in LED "warm-white" light, resulting in metameric failure of orange-to-red objects. Drawing on techniques developed for the architectural restoration of stained glass, we find that transparent, heat-resistant, permanent, pigmented coatings can be applied to any glass, aluminum or plastic surface of an LED bulb, including the phosphor plate, dome or envelope, to produce warmer visible light than in current warm-light LED bulbs. These glazes can be applied in combination with existing technologies to better tune the LED emitted light or they may be used alone. These pigmented coatings include, but are not limited to, those made by suspending inorganic materials in potassium silicates or durable transparent pigmented resins. The pigmented resin glazes may be produced in either a clear gloss vehicle or an iridescent, light diffusing transparent base. Further, a graduated density of the tinted glazes on dimmable bulbs allow the light to change color as wattage is diminished. The glazes may be applied in the manufacturing of the bulb or marketed to current bulb owners as an after-market product to better tune the thousands of LED light bulbs currently in use.

Color temperature, intensity and blue spectrum of the light affects the ganglion receptors in human brain stimulating the human nervous system. With this work we review different methods for obtaining tunable light emission spectra and propose an innovative white LED lighting system. By an in depth study of the thermal, electrical and optical characteristics of GaN and GaP based compound semiconductors for optoelectronics a specific tunable spectra has been designed. The proposed tunable white LED system is able to achieve high CRI (above 95) in a large CCT range (3000 - 5000K).

A nitrogen oxides (NOx) and sulfur dioxide (SO₂) gas analyzer using deep ultraviolet (DUV) and violet light- emitting diodes (LEDs) is developed. The LEDs with wavelengths of 280 nm and 400 nm were alternately turned on to detect SO₂ and nitrogen dioxide (NO₂) absorption. Nitric oxide (NO) was converted to NO₂ with an ozonizer. In order to reduce water interference caused by water adsorption onto an inner surface of a gas ow cell, collimating optics reducing re ected lights were designed. As a result, less than 1% by full scale (%F.S.) of uctuation, 2%F.S. of drift and 0.5%F.S. of water interference were achieved in 0-50 ppm concentration range. Conversion efficiency from NO to NO₂ was over 95%.

Tunable polychromatic light emission within the low color correlated temperature range was produced using terbiumand/ or erbium-samarium co-doped PbGeO₃:PbF₂:CdF₂ glass phosphor. The phosphors were synthesized, and their luminescence characteristics were examined under UV-blue light-emitting-diode laser excitation. Luminescence emission around 490, 545, 600, and 645 nm in Tb³⁺/Sm³⁺ and 525, 545, 600, and 645 nm in Er³⁺/Sm³⁺ co-doped phosphor was obtained and analyzed as a function of the active ions concentration, and excitation wavelength. Color tunability in the red-orange-yellow-green region was achieved combining of Tb³⁺, Er³⁺, and Sm³⁺ ions contents. Results suggest that the color-tunable polychromatic light emitter phosphor herein reported is a promising novel candidate for application in cold white-light LED-based illumination technology

We study nano-grated surface GaN LED to improve light extraction efficiency by optimizing the device parameters. Our study is based on rigorous coupled wave analysis (RCWA) to obtain total transmission across a device. Our simulation results allow us to optimize the device parameters to maximize light extraction efficiency. We simulate our device using a two-dimensional model with square-grating cells in a crystal lattice arrangement whose parameters we define as follows: grating cell period (Λ), grating cell height (d), and grating cell width (ω). We also define grating layer location (L) as the distance between the multi-quantum wells (MQW) source and the grating surface layer. Each simulation varies in grating cell period, grating cell width, and grating layer location and provides a result of total transmission across the device. These results are used to calculate improvement over the non-grated surface GaN LED. Our preliminary study focused on 50% fill factor and showed that location of the grating as well as the grating period both strongly effect the total transmission across the device. In addition, we noticed that optimizing the surface grating location might affect the total transmission. Our study allowed us to improve the light extraction efficiency of nano-grated GaN LED by an average of 133% when fill factor is 50%. We also present our study in detail which includes fill factors ranging between 0 to 100%.

The high-temperature operation of glass based phosphor-converted warm-white light-emitting diodes (PC-WWLEDs) is demonstrated. The fabrication and characteristics of low-temperature phosphor (Yollow:Ce:³⁺:YAG, Greed:Tb³⁺:YAG, Red:CaAlClSiN₃:Eu²⁺) doped glass applied to high color rendering indices warm-white-light-emitting diodes was presented. In this property is color coordinates (x, y) = (0.32, 0.28), quantum yield (QY) = 55%, color rending index (CRI) =85, correlated color temperature (CCT) =3900K. The result showed the PC-WLEDs maintained good thermal stability at the high temperature operation. The QY decay, CRI attenuation and chromaticity shift in glass and silicone based high-power PC-WLEDs under thermal aging at 150°C and 250°C are also presented and compared. The result indicated that the glass based PC-WLEDs exhibited better thermal stability than the silicone. And the color rendering indices (CRI) glass phosphor may have potential used as a phosphor layer for high-performance and low-cost PCWLEDs used in next-generation indoors solid-state lighting applications.

Rare earth doped Y₂CaZnO₅ nanophosphors were synthesized via the citrate-gel combustion method. Transmission electron microscopy measurements reveal that the particles are distributed uniformly within the size range of 10-30 nm. The Er³⁺-doped Y₂CaZnO₅ nanophosphors show strong green upconversion luminescence, which is visible to the naked eye even at 20 mW excitation power of 980 nm diode laser. When these phosphors are codoped with Yb³⁺ ions, the emission changed to reddish color at higher Yb³⁺ ion concentrations. Moreover, these phosphors emitted bright white light luminescence when it is triply doped with Er³⁺/Tm ³⁺/Yb³⁺ ions, indicates Y₂CaZnO₅ nanophosphors are an ideal candidate for phosphor converted white light emitting diodes.

Tobacco is one of the most important economic crops in the world, assessment of its quality has a very important business significance. A compact, low-cost, and maneuverable optical sensor system for classification evaluation of different tobaccos was described in this paper using light-emitting-diodes (LEDs)-induced fluorescence. The principal components analysis (PCA) method is used to extract the dominant features of the tobaccos for identifying the classification of tobaccos. The technique is suitable for practical identification due to the use of a straightforward data evaluation method and compact system.

A compact and low-cost light-emitting diode (LED) with center wavelength of 295 nm and high light density was used measure the concentration of sulfur dioxide, which has a strong structured absorption band in the ultraviolet region 300 nm. Differential optical absorption spectroscopy (DOAS) was used to determine the concentration of sulfur dioxide using reference absorption spectrum due to 1000 ppm SO₂. A sensitivity of about 1.5 ppm was achieved with a gas cell in 1-s integration time, enabling real-time monitoring of sulfur dioxide.

Carrier transport in double heterostructure (DH) InGaN light emitting diodes (LEDs) was investigated using photocurrent measurements performed under CW HeCd laser (325 nm wavelength) excitation. The effect of electron injector thicknesses was investigated by monitoring the excitation density and applied bias dependent escape of photogenerated carriers from the active region and through energy band structure and carrier transport simulations using Silvaco Atlas. For quad (4x) 3-nm DH LED structures incorporating staircase electron injectors (SEIs), photocurrent increased with SEI thickness due to reduced effective barrier opposing carrier escape from the active region as confirmed by simulations. The carrier leakage percentile at -3V bias and 280 Wcm^-2 optical excitation density increased from 24 % to 55 % when In _0.04Ga_0.96N + In_0.08Ga_0.92N SEI thickness was increased from 4 nm + 4 nm to 30 nm + 30 nm. The increased leakage with thicker SEI correlates with increased carrier overflow under forward bias.

We report the growth and characterization of a Si-doped, n-type AlGaN layer with 45% Al composition. For the application of n-type AlGaN layers with high Al composition in ultraviolet emitters, we fabricated an n-Al_0.45Ga_0.55N layer with high crystalline quality and high electrical conductivity by inserting Al_0.85Ga_0.15N/AlN superlattices (SLs) to prevent cracks prior to growing the n-type AlGaN layer. The dislocation density in the n-AlGaN layer with 45% Al composition and SLs was less than 2.4 x 10¹⁰ cm^-2, which was lower than the dislocation density of 5.3 x 10¹⁰ cm^-2 for the n-AlGaN layer without SLs. The resistivity, mobility, and free electron concentration in the n-type Al_0.45Ga_0.55N layer with SLs were 2.2 x 10^-2 Ω×cm, 55.0 cm² /V-s, and 5.0 x 10¹⁸ cm^-3 at room temperature, respectively.

It is believed that low power conversion efficiency in commercial MQW LEDs occurs as a result of efficiency droop, current-induced dynamic degradation of the internal quantum efficiency, injection efficiency, and extraction efficiency. Broadly speaking, all these “quenching” mechanisms could be referred to as the optical losses. The vast advances of high-power InGaN and AlGaInP MQW LEDs have been achieved by addressing these losses. In contrast to these studies, in this paper we consider an alternative approach to make high-power LEDs more efficient. We identify current-induced electrical efficiency degradation (EED) as a strong limiting factor of power conversion efficiency. We found that EED is caused by current crowding followed by an increase in current-induced series resistance of a device. By decreasing the current spreading length, EED also causes the optical efficiency to degrade and stands for an important aspect of LED performance. This paper gives scientists the opportunity to look for different attributes of EED.

In this work, the development of a portable fluorescence spectroscopy platform for Huanglongbing (HLB) citrus disease in situ detection is presented. The equipment consists of an excitation blue LED light source, a commercial miniature spectrometer and embedded software. Measurements of healthy, HLB-symptomatic and HLB-asymptomatic citrus leafs were performed. Leafs were excited with the blue LED and their fluorescence spectra collected. Embedded electronics and software were responsible for the spectrum processing and classification via partial least squares regression. Global success rates above 80% and 100% distinction of healthy and HLB-symptomatic leafs were obtained.

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