Blue Light-emitting Diode Chip Research Articles

Comparison of the Changes in Luminescence Properties Between Cool White and Warm White LEDs at Varying Temperatures

The changes of luminescence properties in cool white (CW) and warm white (WW) light-emitting diodes (LEDs) in response to operating temperatures are compared in this paper. In addition, the emission spectrum of blue LED chips was characterized under the same experimental conditions for cross-reference analysis. The yellow YAG (Y3Al5O12:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ) and red nitrididosilicate (Sr2Si5N8:Eu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) phosphors were synthesized in-house and packed at different concentration configurations to create LED samples of correlated color temperature 6500 K for CW LEDs and 2700 K for WW LEDs. The emission spectrum measurements showed drastic decrements of light emission intensities for both CW and WW LED samples at elevated temperature. Both CW and WW LED samples tend to have more bluish hue with increasing temperatures. Furthermore, the trend of color rendering index (CRI) changes of CW and WW LEDs has differed, a finding that is not commonly reported in other studies. The CRI of CW LED samples increased, whereas the CRI of WW LED samples decreased at elevated temperature. This is due to different shift directions of peak emission wavelength in yellow Y3Al5O12:Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and red Sr2Si5N8:Eu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> phosphors.

Fabrication and optical properties of divalent Cu2+ ions incorporated Ce:YAG transparent ceramics for white LEDs

Transparent Ce:YAG ceramics via Cu2+ incorporating annealed at 1450 °C were successfully fabricated by the solid-state method to probe their potential applications in white light-emitting diodes (LEDs). The influence of Cu2+ concentration on the microstructure and optical properties of the Ce:YAG transparent ceramics were systematically investigated. The as-prepared ceramics possessed clean grain boundaries and homogeneous grain size distribution ranging from 3.7 to 6.5 µm. With the addition amount of Cu2+ increased, the red component of ceramics gradually increased and then decreased, it reached a maximum of 13.0% at 1.5 at% Cu2+ incorporation. By combining with commercially blue LED chips (465 nm) directly, the obtained optimal chromaticity coordinates (CIE) and correlated color temperature (CCT) of ceramics were (x = 0.3335, y = 0.3412) and 5450 K, respectively, while its color render index (CRI) was nearly 70 at the thickness of 1.0 mm. Therefore, this study provided an efficient approach to tailor the luminescence property of Ce:YAG ceramic for white LEDs.

A Comparative Study on the Junction Temperature Measurements of LEDs With Raman Spectroscopy, Microinfrared (IR) Imaging, and Forward Voltage Methods

Energy efficiency, long life, exceptional color, and performance of solid-state light sources have resulted in a rapidly increasing trend in a number of practical applications especially for general lighting after a long history of incandescent lamps. Besides, light-emitting diodes (LEDs) have thermal limitations that are vital for device quality and lifetime. Specifically, to improve the heat dissipation, one major parameter used to evaluate the LED performance is thermal resistance ( $R$ ). Reducing the resistance can improve the heat flow from the p-n junction to ambient during operation. To quantify this parameter, the LED junction temperature ( $T_{J}$ ) must be determined. In this paper, the junction temperatures are first measured with forward voltage method (FVM), Raman spectroscopy, and infrared (IR) imaging for a 465-nm bare blue LED chip (without any phosphor coating). Then, the same samples have been coated with a phosphor-particles added epoxy mixture (%13, 4300 CCT) to convert blue to white light, and the junction temperatures were measured again experimentally with the previously mentioned three methods and compared to each other. While IR imaging shows better capability on capturing the possible hotspots over the surface, Raman method and FVM were in reasonably good agreement on measuring the junction temperature for 465-nm blue (uncoated) LED chip. However, the measurements performed after coating have shown slightly different results with IR imaging and Raman methods, while FVM has shown consistent results for coated chips.

Mechanism for Forming Quantum-Size AlGaN/GaN/InGaN/GaN Heterostructure Layers

The use of silicon in optoelectronic elements and microwave devices is limited by its electrical properties. In this range of application, silicon is replaced by wider-gap materials, e.g., GaN, AlN, InN, and solid solutions based on them. This allows highly efficient devices, including light-emitting diodes and photodetectors operating in a wide radiation spectral range, to be fabricated. In addition, GaN-based materials have been successfully used in designing high-power microwave devices, in particular, transistors with highly mobile electrons operating at high temperatures. We discuss specific features of the technology for fabricating active layers in the AlGaN/GaN/InGaN/GaN heterostructures with the use of metalorganic compounds. The initial substances used are ultra-pure ammonia NH3 and gallium, aluminum, and indium metalorganic compounds in the trimethyl form. The temperature dependence of the epitaxial GaN layer growth rate is investigated. This dependence is shown to be weak in a wide temperature range. The importance of adsorption processes occurring on the growth surfaces is confirmed. Thermodynamical analysis of the regularities of the investigated process is carried out to simulate the process and establish the conditions for forming GaN-based solid solutions. It is shown that during the formation of Ga1 – xInxN solid solutions in the high-temperature region the attainable InN content is not higher than 0.4 mole fractions. As the growth temperature decreases to 600°С, the conditions for incorporating In in the solid solution are noticeably improved and the InN concentration increases to 0.9 mole fractions. It is demonstrated that growing the GaAlN solid solutions in a wide temperature range makes it possible to obtain the AlN content ranging from 0.1 to 0.9 mole fractions. The experimental investigations are confirmed by the calculations. Therefore, when growing the Ga1 – xInxN quantum well layers in the active heterostructural area for commercial blue light-emitting diode chips with an indium content of х = 0.1–0.15, the growth temperature should be reduced. At low temperatures, however, it is difficult to grow epitaxial layers with a high crystal quality.

Effect of Gd3+ , Bi3+ , or Sm3+ on luminescent properties of La2-x MgTiO6 :xEu3+ phosphors.

Single phase of Bi3+ , Gd3+ , Sm3+ and Eu3+ co-doped La2 MgTiO6 red phosphors were synthesized by high temperature solid-state method. The phase composition, morphology and fluorescent properties of the phosphors were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrometer. The La2-x MgTiO6 :xEu3+ phosphors can be excited by UV (396nm) and blue (465nm) light-emitting diode (LED) chips and show a strong red emitting with dominated wavelength at 615nm. The optimum doping concentration of Eu3+ ion for La2 MgTiO6 is x=0.5. The luminescent intensities of 5 D0 →7 F2 transition of Eu3+ in La1.5-y MgTiO6 :0.5Eu3+ , yBi3+ /Gd3+ /Sm3+ were 1.31 times, 1.32 times and 1.88 times that of La1.5 MgTiO6 :0.5Eu3+ at y=0.08, 0.06, 0.06 for Bi3+ , Gd3+ , or Sm3+ sensitizer, respectively. The chromaticity coordinates of La1.44 MgTiO6 :0.5Eu3+ , 0.06Sm3+ , (0.6342, 0.3513) were very close to those of the National Television Standard Committee (NTSC) standard red light coordinates.

Simple prismatic patterning approach for nearly room-temperature processed planar remote phosphor layers for enhanced white luminescence efficiency

Efforts have been made to enhance light-extraction by controlling phosphor structure for higher efficiency white light-emitting diodes (LEDs). Here, we introduce a technical method for improving luminous efficacy by applying prismatic patterns for a planar remote yellow phosphor structure. The remote phosphor structure is based on a UV-cured prismatic pattern/polyethylene terephthalate (PET)/glass substrate/silicate phosphor layer. The phosphor layer was formed via another UV-curing process of the screen-printed polymer/ phosphor-mixture. As a result, the prismatic layer of the apex angle 90° of each pitch enhanced the luminous efficacy of the remote phosphor-LED by 29% compared with the reference sample when a smaller pitch size was used. As anticipated, it is assumed that the escape probability of the emitted lights from a blue LED chip through the phosphor structure increases by reducing the possibilities of total internal reflection at the top surfaces of the structure.

Effect of the Electronic Structure on the Stability of CdSe/CdS and CdSe/CdS/ZnS Quantum-Dot Phosphors Incorporated into a Silica/Alumina Monolith

In this letter, we prepare ultrastable quantum-dot (QD)-based phosphors. Furthermore, we find that type I CdSe/CdS/ZnS QDs are fairly stable during the thermal annealing process of a QD–SiO2/Al2O3 monolith (SAM) phosphor, but quasi-type II CdSe/CdS QDs easily lose their emission possibly because the delocalized electrons to the shell are more susceptible to being captured by the surface trap sites. The light-emitting diode (LED) encapsulated with a CdSe/CdS/ZnS QD–SAM phosphor on the blue LED chip can maintain approximately 90% of its initial intensity after 450 h, in contrast, the light intensity of the reference LED using a CdSe/CdS/ZnS QD decreases to approximately 41%.

Red Luminescent Eu(III) Coordination Bricks Excited on Blue LED Chip.

Three types of red luminescent Eu(III) complexes with Schiff base and hfa ligands (hfa: hexafluoroacetylacetonate), mononuclear [Eu(hfa)2(OAc)(salen)2] (OAc: acetate anion, salen: N,N'-bis(salicylidene)ethylenediamine), brick-type [Eu2(hfa)4(OAc)2(salbn)2] (salbn: N,N'-bis(salicylidene)-1,4-butanediamine), and polynuclear [Eu(hfa)2(OAc)(salhen)] n (salhen: N,N'-bis(salicylidene)-1,6-hexanediamine) are reported for white light-emitting diode (LED) devices. Among these complexes, brick-type [Eu2(hfa)4(OAc)2(salbn)2] excited by blue light (460 nm) exhibits the photosensitized quantum yield (Φπ-π* = 47%) and remarkably high efficiency of sensitization (ηsens = 96%). The efficiency of sensitization is caused by the excited state based on ligand-ligand interaction between the Schiff base and hfa ligands in Eu(III) complexes. To fabricate LED devices, the red luminescent [Eu2(hfa)4(OAc)2(salbn)2] was mounted on an InGaN blue LED chip.

Liquid-type inorganic perovskite CsPbBr1.2I1.8 quantum dots for white light-emitting diode

In this study, inorganic perovskite CsPbBr1.2I1.8 quantum dots (QDs) were synthesized and their luminescence properties were investigated in detail. For the first time, a hybrid white light-emitting diode (LED) was fabricated by combining the Y3Al5O12:Ce3+ phosphors (YAG) and liquid-type CsPbBr1.2I1.8 QDs with a blue LED chip. This liquid-type CsPbBr1.2I1.8 QDs-modified LED (LQD-LED) shows excellent optical performances with luminous efficacy (LE) of 91 lm W−1, correlated color temperature (CCT) of 5112 K, and color rendering index (CRI) of 88, at an operation current of 20 mA. More importantly, the optical performances of the LQD-LED do not exhibit serious degeneration when the device is working under a higher operation current (350 mA) for longer operation time (100 h), which are superior to other solid-type QDs-modified LEDs (SQD-LEDs) reported previously. We believe that this liquid encapsulation structure LED would be applied to high-power lighting in the near future.

Effect of Phosphor Layer Size on the Optical and Thermal Properties of Chip Scale Packaged Light-Emitting Diodes

Light-emitting diodes (LEDs) have been widely applied for backlight unit for displays, general lighting, and automotive illumination because they have a high light efficiency and long life time, and are environmentally friendly. These diverse applications require smaller and slim LED chip scale packages (CSPs). CSP LEDs have been developed to produce white LED chips by forming a thin phosphor film on blue LED chips. In this study, we investigated the effect of phosphor layer thickness and area on the optical and thermal properties of the CSP LEDs. The phosphor-conversion of chips is maximized by varying the thickness and area of the phosphor layer. Eight different types of phosphor-converted white CSPs with normal performance (CRI > 70, CCT ~ 5700 K) were prepared by using mixed multicolor phosphor materials. In other words, for five samples whose CSP area was fixed at 1.8 x 1.8 mm2, flip-chip area was 1.4 x 1.4 mm2, and flip-chip thickness was 250 μm, the thickness of the phosphor layers was varied from 100 to 500 μm at intervals of 100 μm. For other three samples where the phosphor layer thickness was fixed at 300 μm, the flip-chip area was 1.4 x 1.4 mm2, and flip-chip thickness was 250 μm, the CSPs had three different areas of 1.6 x 1.6, 1.8 x 1.8, and 2.0 x 2.0 mm2. First, the relative luminous flux and LED beam distribution were characterized using integrating sphere and a goniometer. It was shown that as the thickness of the phosphor layer increased, the luminous flux and the directivity angle increased. On the other hand, as the CSP area increased, the luminous flux and the directivity angle decreased. This could be attributed to the fact that CSP does not have a reflector (namely, a housing material) and so the blue light of the chip does not excite the whole area of the phosphor. This may be confirmed by the images showing light distribution and luminescence characteristics, which is currently under investigation. Furthermore, a junction temperature measurement system was used to characterize the junction temperatures of the five different samples whose phosphor layer thicknesses were varied from 100 to 500 μm. It was found that when the thickness of the phosphor layer exceeded the thickness of the chips (250 μm), the junction temperature of the samples dramatically increased. Further details regarding the phosphor layer thickness of the junction temperature characteristics will be investigated and described.

Synthesis of Mn-doped CuGaS_2 quantum dots and their application as single downconverters for high-color rendering solid-state lighting devices

Photoluminescence (PL) of quantum dots (QDs) can be modulated by doping transition metal ions into them, yielding either only a dopant-related single PL band with an excitonic emission entirely quenched or multiple PL bands with a dopant-related PL superposed, depending on the host QD composition targeted. Herein, we attempt Mn doping into green-emitting CuGaS2 (CGS) QDs through surface adsorption and lattice diffusion strategy. The resulting Mn-doped, ZnS-shelled CGS or CGS:Mn/ZnS QDs exhibit two distinct PL bands associated with host QD defect and dopant emissions. The spectral ratio of such two PL components is facilely tunable by varying Mn concentration. A series of CGS:Mn/ZnS QDs possess high PL quantum yields in the range of 74–76% regardless of Mn concentration. Taking full advantage of the wide PL coverage of green-to-red and efficient absorption capability at the blue region of the present doped QDs, they are packaged as single downconverters with a blue light-emitting diode (LED) chip to fabricate a high-color rendering solid-state lighting device. Various electroluminescent characteristics of white QD-LED are evaluated as a function of QD doping concentration and input current and discussed in detail.

Photonic Crystal Phosphors Integrated on a Blue LED Chip for Efficient White Light Generation.

Following the proof-of-concept experiment in the unit structure level, photonic crystal (PhC) phosphors-structurally engineered phosphor materials based on the nanophotonics principles-are integrated with a blue light-emitting diode (LED) chip to demonstrate a compact and efficient white light source. Red- or green-emitting CdSe-based colloidal quantum dots (CQDs) are coated on a Si3 N4 thin-film grating to fabricate PhC phosphors. The underlying PhC structure is designed such that the photonic band-edge modes at the zone center (k∣∣ = 0) are tuned to the energy of the blue excitation photons. By progressively stacking the PhC phosphor plates on a blue LED chip, the blue, green, and red emission intensities can be tightly controlled to obtain white light with the desired properties. The chromaticity coordinates, (0.332, 0.341), and correlated color temperature, 5500 K, are obtained from a stack of 3 red and 11 green PhC phosphor plates; in contrast, a stack of 5 red and 16 green reference phosphor plates are required to generate a similar white light. Overall, the PhC phosphors produce 8% higher total emission intensity out of 33% less amount of CQDs than the reference phosphors.

A Fast Method for Lifetime Estimation of Blue Light-Emitting Diode Chips Based on Nonradiative Recombination Defects

This paper proposes a new method for estimating the lifetime of the InGaN/GaN-based light-emitting diode (LED) chip by analysing the density of nonradiative recombination defects. The nonradiative recombination defect is a major factor affecting the performance of LED chips, and the increase in defects eventually leads to the chip failure. Therefore, the growth rate of defects determines the lifetime of the LED chip. A new measurement method of the defect density is introduced. A batch of 1-W blue LED chips is selected to conduct 6000-h accelerated life tests with constant current stresses. And through studying the data of defect densities and light output, it is concluded that compared with light output, the defect density is more sensitive to the current stress, which indicates that the defect density is more advantageous to reflect the performance degradation of the LED chip. In particular, the growth of defects induced by aging stress is found to follow a logarithmic law, then a mathematical model of the defect growth is introduced. And with the model we can obtain the key parameters about the growth rate of defects. Furthermore, we establish the quantitative relationship between the growth rate of defects and aging lifetime. Based on this relationship, the lifetime of the LED chip can be predicted in a more accurate and faster way. The result shows that under the stress condition of our experiments, this new method requires less than 1000-h stress time, and the traditional method requires more than 6000 h.

Color Shift Failure Prediction for Phosphor-Converted White LEDs by Modeling Features of Spectral Power Distribution with a Nonlinear Filter Approach.

With the expanding application of light-emitting diodes (LEDs), the color quality of white LEDs has attracted much attention in several color-sensitive application fields, such as museum lighting, healthcare lighting and displays. Reliability concerns for white LEDs are changing from the luminous efficiency to color quality. However, most of the current available research on the reliability of LEDs is still focused on luminous flux depreciation rather than color shift failure. The spectral power distribution (SPD), defined as the radiant power distribution emitted by a light source at a range of visible wavelength, contains the most fundamental luminescence mechanisms of a light source. SPD is used as the quantitative inference of an LED’s optical characteristics, including color coordinates that are widely used to represent the color shift process. Thus, to model the color shift failure of white LEDs during aging, this paper first extracts the features of an SPD, representing the characteristics of blue LED chips and phosphors, by multi-peak curve-fitting and modeling them with statistical functions. Then, because the shift processes of extracted features in aged LEDs are always nonlinear, a nonlinear state-space model is then developed to predict the color shift failure time within a self-adaptive particle filter framework. The results show that: (1) the failure mechanisms of LEDs can be identified by analyzing the extracted features of SPD with statistical curve-fitting and (2) the developed method can dynamically and accurately predict the color coordinates, correlated color temperatures (CCTs), and color rendering indexes (CRIs) of phosphor-converted (pc)-white LEDs, and also can estimate the residual color life.

Tunable chromaticity and enhanced luminous efficacy of white LEDs with phosphor-in-glass coating via multilayer screen-printing

Abstract The phosphor-in-glass (PiG) coating was fabricated via multilayer screen-printing and low-temperature sintering. The PiG coating consisted of Eu 2 O 3 -doped P 2 O 5 -ZnO-B 2 O 3 (PZB) glass, Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) yellow phosphor, and CaAlSiN 3 :Eu 2+ (CASN:Eu) red phosphor. Eu 2 O 3 and CASN:Eu were used to provide red emission for tunable chromaticity of white light-emitting diodes (LEDs), and surprisingly, the luminous efficacy was also enhanced. The impact of the variation in the B 2 O 3 content on the PZB glass and the effect of Eu 2 O 3 , YAG: Ce, and CASN:Eu on the luminescent properties of the PiG coating were investigated. The glass matrix with 8 mol% B 2 O 3 showed the lowest transition temperature and a suitable coefficient of thermal expansion. The spectra showed that the coating can be excited by blue light and produce yellow light and red light. The spatial distribution of the PiG coating was inspected by scanning electron microscopy, and it was observed that only a low erosion of phosphor by the glass matrix occurred. Furthermore, the white LEDs devices were constructed with the PiG coating on the blue LED chips. This method showed a decreased correlated colour temperature of 5137, a increased colour rendering index of 82.8 and an improvement in the luminous efficacy. The PiG coating for tunable chromaticity and enhanced luminous efficacy of white LEDs shows potential for application.

Photoluminescence properties of broadband deep-red-emitting Na2MgAl10O17:Mn4+ phosphor

A new non-rare-earth deep-red-emitting Na2MgAl10O17:Mn4+ phosphor is prepared successfully by high temperature solid-state reaction method in air. All samples are a single pure phase, which is confirmed by X-ray powder diffractions patterns. Excitation spectrum shows some absorption bands in the range of 220–600 nm, which are line with the wavelength of ultraviolet (UV), near UV, and blue light-emitting diode chips. Deep-red emission of Na2MgAl10O17:Mn4+ phosphor with excitation UV, near UV, and blue light can be observed in the range of 600–810 nm due to the 2E → 4A2 transition of Mn4+ ion in octahedral symmetry with aided the lattice vibration. The full width at half maximum (FWHM) is ∼105 nm. The optimal Mn4+ concentration is ∼1%. Decay curve and time-resolved spectra indicate that there is only a Mn4+ ion luminescent center in Na2MgAl10O17:Mn4+ phosphor. The thermal stability is investigated and analyzed by the configuration coordinate diagram of Mn4+ ion.

Green light–emitting diodes with high efficiency organosilane-functionalized carbon dots

ABSTRACTOrganosilane-functionalized carbon dots (SiCDs) with green emission were prepared by one-step solvothermal method. Anhydrous citric acid and N-(2-aminoethyl)-3-aminopropyltrimethoxy-silane (KH792) were used for the preparation of SiCDs. Green light-emitting diodes (LEDs) were fabricated by combination of a 450 nm-emitting blue LED chips and green SiCDs, since green SiCDs was used to convert blue light to green light. The luminous efficiency of green LEDs can reach 60.96 lm/W. The as-prepared polymerizable SiCDs are hopeful to provide new opportunity to simplify the preparation process and improve optical performances of green LEDs.

Photoluminescence and electric properties of Pr/Nb codoped Bi4Ti3O12 bismuth layered-structure ceramics

Bi4Ti3O12 (BIT) belongs to bismuth-layer structure piezoelectric materials, along with high Curie temperature ( T c) and high resistivity. Pr/Nb co-doped BIT piezoelectric ceramics were synthesized by conventional solid-state reaction method and their structural, up-conversion luminescent and dielectric properties were investigated in this study. The substitution of Nb5+ ion was fixed as 0.08 mol and the amount of Pr3+ was 0≤ x ≤0.1. The X-ray diffraction data showed that the samples were single phase with orthorhombic unit cell, and SEM micrographs revealed that the samples have similar plate-like grain morphology. Raman spectroscopy revealed that Er3+ substitution for Bi3+ occured predominantly at the A-site in the perovskite blocks. The red emission was observed under the ultraviolet and blue light excitation at room temperature, which is adaptable to the emission band of commercial blue light-emitting diodes (LEDs) chips. With increasing Pr3+ content, the intensity of the photoluminescence increased initially and then decreased due to concentration quenching. The T c was slightly shifted to the lower temperature, the piezoelectric and ferroelectric properties was both enhanced by doping. These results indicated the Pr doped BITN ceramics were a kind of multifunctional materials with excellent optical performance.

Tungstate flux-grown Y 10 W 2 O 21 :Eu 3+ phosphors with enhanced particle size and luminescence properties

Abstract Eu 0.5 Y 9.5 W 2 O 21 strong red emission phosphors were synthesized via a conventional solid-state reaction method with environmentally friendly tungstate flux (M 2 WO 4 , M=Li, Na, K). The growth process of the Eu 0.5 Y 9.5 W 2 O 21 phosphors was studied using X-ray diffraction, scanning electron microscopy, and thermogravimetry/differential thermal analysis. The photoluminescence properties, including emission and excitation spectra and thermal stability, were also investigated. The experimental results indicate that the particle size and morphology of the Eu 0.5 Y 9.5 W 2 O 21 phosphors depend on the type and content of tungstate flux. The luminescence intensities of the phosphors were effectively enhanced by the tungstate flux. The results also show that the Eu 0.5 Y 9.5 W 2 O 21 phosphors are very suitable for use in near-ultraviolet light-emitting diode (LED) chips (392 nm) and blue LED chips (465 nm).

Monolithically Integrated Light Feedback Control Circuit for Blue/UV LED Smart Package

Given the performance decay of high-power light-emitting diode (LED) chips over time and package condition changes, having a reliable output light for sensitive applications is a point of concern. In this study, a light feedback control circuit, including blue-selective photodiodes, for blue/ultraviolet (UV) LED, has been designed and implemented using a low-cost seven-mask BiCMOS process. The feedback circuit was monolithically integrated in a package with four high-power blue LED chips. For sensing the intensity of exact colored blue/UV light in the package, selective photodiodes at 480-nm wavelength were implemented. An opamp-based feedback circuit combined with a high-power transistor controls the output light based on real-time sensor data. The whole system is a low-cost integrated package that guarantees a stable and reliable output light under different working conditions. Output light can be also controlled linearly by a reference input voltage.