Light Emitting Diode Headlamp Research Articles

THERMAL ENHANCEMENTS OF A LED BASED AUTOMOTIVE HEADLAMP

Light Emitting Diode (LED) is a new kind of light source that is quickly being used into automotive lighting systems. In recent years, there have been increased expectations placed on vehicle headlamps, including that they not only be fully functional, affordable, and long-lasting, but also stylish, energy-efficient, and environmentally friendly. Since LED light sources are long-lasting, highly efficient, and energy-efficient, small in size, etc., they are frequently utilized in headlamps, turn signals, brake lights, position lights, etc. and will soon dominate the automotive light source industry. Although it has a greater energy conversion efficiency, the thermal management of LED headlamps is still a problem. In this research, the response surface method is used to optimize the heatsink designs for LED automotive headlamp module. The finite element (FE) approach and numerical simulation are used to model the test samples temperature distribution. Then, in order to maximize the heatsink potential for thermal dissipation, we tested different types of material, and used the response surface method. The LED headlamp hot spots decrease by 2 to 8 degrees when the heat sinks thickness, fin spacing, and height are optimized and decrease by 7.64 degrees when the heat sink and PCB substrate are made of 6063 aluminum alloy and AlN, respectively.

The potential ‘blue light hazard’ from LED headlamps

Many dental personnel use light-emitting diode (LED) headlamps for hours every day. The potential retinal ‘blue light hazard’ from these white light headlamps is unknown. MethodsThe spectral radiant powers received from direct and indirect viewing of an electronic tablet, an LED curing light, a halogen headlamp, and 6 brands of LED headlamps were measured using integrating spheres attached to fiberoptic spectroradiometers. The spectral radiant powers were measured both directly and indirectly at a 35 cm distance, and the maximum daily exposure times (tMAX) were calculated from the blue weighted irradiance values. ResultsThe headlamps emitted very different radiant powers, emission spectra, and color temperatures (K). The total powers emitted at zero distance ranged from 47 mW from the halogen headlamp to 378 mW from the most powerful LED headlamp. The color temperatures from the headlamps ranged from 3098 K to 7253 K. The tMAX exposure times in an 8 h day when the headlamps were viewed directly at a distance of 35 cm were: 810 s from the halogen headlamp, 53 to 220 s from the LED headlamps, and 62 s from the LED curing light. Light from the LED headlamps that was reflected back from a white reference tile 35 cm away did not exceed the maximum permissible exposure time for healthy adults. Using a blue dental dam increased the amount of reflected blue light, but tMAX was still greater than 24 h. ConclusionsWhite light LED headlamps emit very different spectra, and they all increase the retinal ‘blue light hazard’ compared to a halogen source. When the headlamps were viewed directly at a distance of 35 cm, the ‘blue light hazard’ from some headlamps was greater than from the LED curing light (tMAX = 62 s). Depending on the headlamp brand, tMAX could be reached after only 53s. The light from the LED headlamps that was reflected back from a white surface that was 35 cm away did not exceed the maximum permissible ocular exposure limits for healthy adults. Clinical relevanceReflected white light from dental headlamps does not pose a blue light hazard for healthy adults. Direct viewing may be hazardous, but the hazard can be prevented by using the appropriate blue-light blocking glasses.

Compact Measurement of the Optical Power in High-Power LED Using a Light-Absorbent Thermal Sensor.

LED (Light-Emitting Diode) presents advantages such as luminescence, reliability, durability compared with conventional lighting. It has been widely applied for life, healthcare, smart farm, industry, and lighting from indoor to the automotive headlamp. However, the LED is vulnerable to thermal damage originated from the high junction temperature, especially in high power applications. Hence, it requires precise qualification on the optical power and the junction temperature from the pilot line to secure reliability. In this study, the photo-thermal sensor is proposed by employing a sheet-type thermocouple composed of photo-absorbent metal film and thermocouple. This sensor aims low-cost qualification in pilot line for high-power luminous devices and optical monitoring of costly luminaire such as automobile LED headlamp. The sensor is designed to detect the increased temperature response of LED hot spots from the transferred thermal power and absorbed optical power. The temperature response of each sheet-type thermocouple is utilized as a signal output of the absorbed optical power and hot spot temperature based on the introduced sensor equation. The proposed thermal sensor is evaluated by comparing the experiment with the measured reference value from the integrating sphere and the attached thermocouple at a junction. The experiment result reveals 3% of the maximum error for the optical power of 645 mW.

Effect of Thermal Interface Materials on Heat Dissipation of Light-Emitting Diode Headlamps with Thermally-Conductive Plastics.

We study the effect of thermal interface material such as thermal-conductive plastic on the dissipation of generated heat from the light-emitting diodes (LEDs) based headlamp for the application of environment-friendly green energy in vehicles. The thermal distribution and the performances of thermal-conductive plastic with heatsink are consistently investigated by using experimental and numerical results. Various thicknesses of thermal-conductive plastics from 0.3 mm to 1.0 mm used in this research work. Basically the thermal-conductive plastic reduces the thermal interface resistance between the contact of two solid surfaces. As a result, High electrical power of about 15 W (1 A and 15 V) can be possible for applying to the high-power LED package without any damage. The soldering temperature of LED package without thermal-conductive plastic shows approximately 138.7 °C which is higher compared to the LED package with thermal-conductive plastic (124.3 °C). On the other hand, the soldering temperature increases from 124.3 to 127.6 °C with increasing the thicknesses of thermal-conductive plastic. In addition, the soldering temperature decreases from 138.7 to 124.3 °C with increasing the thermal conductivities of thermal-conductive plastic. Finally, a highly thermal conductive property of thermal-conductive plastic will propose for optimum dissipation of generated heat from the LEDs-based headlamp. We also successfully estimate the junction temperature of packaged LEDs by using soldering temperature.

Development of Multi-DOF Model of Automotive LED Headlamp Assembly for Force Transmission Prediction Using MATLAB GUI

The use of Light-emitting diodes (LEDs) in automobile headlamps began two decades ago. Since then, several design and efficiency improvements have been made. However, the reliability and durability of these LED systems remain uncertain. There are several approaches for reliability analysis, e.g., thermal, electrical, optical, or structural. The first three issues have been studied in the past, but there has been minimal focus on structural and dynamic durability. Uneven road conditions and impact forces acting on the headlamp module can damage components and misalign the aiming mechanism. Moreover, the functionality could be disturbed, thereby decreasing the efficiency of the system. To determine the forces acting inside the module on each component, this study proposes a simulation technique for predicting the magnitude of forces transmitted from the automobile chassis to the headlamp module under even and uneven road conditions. A vibration system with 23 degrees-of-freedom is developed and equations of motion are derived using Newton’s second law of motion. Solving this system of equations with Simulink and MATLAB provided the linear and angular displacements of each element, which were then utilized to calculate the forces transmitted through these elements. Two forcing conditions were compared and the locations with maximum forces are highlighted.

Cooling of LED headlamp in automotive by heat pipes

Trends in automotive headlamps are changing from halogen/xeon towards light emitting diode (LED) type light functions. LEDs have 2 times higher light efficiency, longer illumination distance, 10–15 times longer lifetime and better styling features than halogen lamps. Unlike halogens, LEDs need temperature control to maintain their monochromaticity, light intensity and longevity. A typical LED headlamp can dissipate 25 to 70 W heat load depending on light functions and styling features. Traditionally, aluminum die cast heat sinks are used as cooling solution for LEDs, which are thermally low efficient and structurally heavy and space intensive. In the present investigation, heat pipe based cooling systems for different designs and styles of LED headlamps and thermal capability of up to 20 W/per-module have been proposed, designed and characterized. Heat pipe configurations include 6–8 mm diameter, 200–400 mm length, copper wick/container and water as working fluid. In combination with different heat sink designs and cooling options, heat pipes can provide 2 to 3 times higher heat capability and up to 50% lighter cooling module, as compared to die cast heat sinks. Based on requirements from headlamp manufacturers, different innovative designs of heat pipes, including high-performance cylindrical/flattened copper-water heat pipe for low/high beam cooling, hinge heat pipe for adaptive headlamp with swivel function cooling and flexible heat pipe for remotely mounted heat sink, has been developed. Heat pipes due to their ultra-high thermal conductivity (~5000 W/m.K or higher) can drastically improve heat dissipation capability of heat sink (natural or fan cooled) and allow different heat sink design options (chassis/frame type, die cast type, stacked-thin-fin type). This allows for better space utilizations inside headlamps, possibility of fully passively cooled headlamps and shared heat sinks between different light functions. LED headlamp with heat pipe thermal modules will tend to be cooler, lightweight and compact.

Novel Wavelength-Specific Blue Light−Emitting Headlamp for 5-Aminolevulinic Acid Fluorescence-Guided Resection of Glioblastoma

Extent of resection of glioblastoma is an important predictor for overall survival, and 5-aminolevulinic acid fluorescence-guided surgery can improve outcomes. However, the technique requires the installation of a blue light module on operative microscopes and may be cost prohibitive. A novel and economical blue light-emitting headlamp was designed, and its clinical utility was explored. A remote-controlled dual light emitting diode headlamp system was constructed with 1 diode emitting white light and the other blue. Spectrographic analysis of the blue light emitted from a commercial operative microscope and the headlamp was performed. A comparative evaluation of the 2 illumination systems was conducted for 3 patients who underwent craniotomy for glioblastoma resection. Histologic examination of the fluorescing tissue detected by the headlamp was performed, and the extent of resection was assessed by postoperative day 1 magnetic resonance imaging. Spectrography of blue light emitted from the headlamp system was wavelength specific with a single emission peak at 416 nm and a linewidth of 35 nm. In contrast, blue light from the microscope (peak: 426 nm) had a wider linewidth of 54 nm and was not wavelength specific with additional infrared radiation detected. Gross or near-total resection of contrast-enhancing glioblastoma was performed for all 3 patients. Intraoperatively, comparable tumor fluorescence was observed under microscope and headlamp blue light illumination. Histologic examination of tissue fluorescing under headlamp blue light confirmed the presence of glioblastoma. This novel proof-of-concept blue light-emitting headlamp device may offer an opportunity for institutions with limited resources to implement 5-aminolevulinic acid fluorescence-guided glioblastoma resections.

Is the Intensity of 5-Aminolevulinic Acid–Derived Fluorescence Related to the Light Source?

With the introduction of the 5-aminolevulinic acid (5-ALA) technique, surgical neuro-oncology has made a major advance. 5-ALA fluorescence-guided resection of malignant glioma results in more complete surgical resections and subsequently prolonged survival. However, it remains uncertain how light intensities of the blue light source and 5-ALA-derived fluorescence intensities of the illuminated tissue are connected. The aim of the present study was to compare light intensities of different blue light sources and protoporphyrin (PpIX) fluorescence intensities of PpIX solutions with defined concentrations after illumination with different light sources. The light spectrum of 7 different blue light sources and the fluorescence intensity of 2 PpIX solutions (0.15 μg/mL and 5 μg/mL) were quantified after illumination. We compared the Zeiss OPMI Pentero microscope, the Zeiss OPMI Pentero 900 microscope, the Leica M530 OH6 microscope, an endoscope equipped with the 5-ALA technique, a mini-spectrometer equipped with a multi-channel light-emitting diode (LED) source emitting monochromatic light, a modified commercially available LED head lamp, and a commercially available unmodified UV-LED lamp. PpIX fluorescence was quantified in a standardized setup using a mini-spectrometer. Maximum light intensities of the evaluated light sources were reached at different wavelengths. All tested devices were able to detect PpIX-induced fluorescence. However, the intensity of PpIX fluorescence of the differently concentrated PpIX solutions (0.15 μg/mL and 5 μg/mL) was significantly dependent on the light source used. Intensity of the 5-ALA-derived fluorescence is related to the light source used.

Improvement in the heat dissipation of matrix LED headlamps for vehicles according to the thickness and thermal conductivity of thermal interface materials

This study examined the effects of thermal interface materials (TIMs) in light-emitting diode (LED) headlamps for vehicles based on thermally conductive plastics. Heat transfer is a very important issue in LED applications because the stability and performance of LEDs decrease considerably with increasing junction temperature. When two solid surfaces are placed in contact, a TIM is used to reduce the thermal interface resistance. This study examined the effects of the thickness (0.3, 0.5, and 1.0 mm) and thermal conductivity (1.8, 3.0, 5.0, and 11.0 W m−1 K−1) of a TIM on the soldering temperature (TS). TS increased with increasing TIM thickness. In addition, TS decreased with increasing thermal conductivity of the TIM. The junction temperature (TJ) was lower than the others when a TIM with a high thermal conductivity of 11 W m−1 K−1 was used. Overall, the TJ and TS can be reduced using a suitable high thermal conductivity TIM with an appropriate thickness.

Experimental investigation on the thermal performance of a light emitting diode headlamp with a flexible woven heat sink

Flexible woven heat sink (FWHS) is proposed to meet the heat-dissipation demand of a light emitting diode headlamp, which can be installed in limited spaces. The heat sink comprises three copper belts manufactured by weaving copper wires, with a structural advantage of high flexibility. The thermal-resistance network model of the headlamp with the FWHS was established. A test system was implemented to analyze the factors affecting the heat transfer, such as the expanded forms, input power, ambient temperature, and wind speed. The expanded form of the FWHS can be adjusted by changing the inclination angles α and β. α means the inclined angle between the adjacent woven belts, and β means the inclined angle of each woven belt expanded along the folding part. The optimal expanded form is the status with α=25–90° and β=25–40°. The overall temperature of the headlamp increases almost linearly with the increase in the input power and the ambient temperature. The cooling effect of the FWHS is enhanced with the increase in the wind speed; the optimal wind speed is approximately 2m/s.

Analysis of Factors Influencing on Heat Transfer Characteristics of Automobile LED Headlamp

Light Emitting Diodes (LEDs) are being considered for use in the automobile headlamps for front side illumination in the place of halogen and xenon headlamp systems. Although LEDs provide larger service life and better power efficiency, they generate considerable amount of heat. It is desirable to develop an advanced cooling system to effectively dissipate heat generated for a stable, continuous and reliable LED operation. The objective of this investigation is to experimentally study the factors influencing the cooling performance of the air cooled heat sink model used in an automobile LED headlamp system. The cooling performance of the heat sink model under consideration was assessed by measuring temperature and thermal resistance at significant locations. The input power, fan output and ambient temperature were varied and corresponding effects were observed. The effect of power variation on illuminance was observed. In addition, a comparative study was carried out to determine the effects of forced and natural convection, which indicated the necessity of forced convection for effective cooling of an automobile LED system.

열전도성 플라스틱을 적용한 자동차 LED 전조등 방열구조 연구

Since LEDs (light emitting diodes) have many advantages as a light source in vehicle headlamp, such as good reliability, energy and space saving, and flexible headlamp design. On the other hand, the dependence of its performance and life on temperature have great influence on its practical use. In this study, design and fabrication of heat sink for vehicle LED headlamp were performed using thermally-conductive plastics. This study focused on the effective heat sink structure with limited space in the vehicle LED headlamp. We designed two different prototype of heat sink by thermal simulation using SolidWorks program, which had excellent temperature characteristics. The two different prototype of heat sink were fabricated by injection molding with thermally-conductive plastics. The results showed that LED (junction temperature) of sample B (model 1) and sample C (model 1, 2) was below then when applying the thermally-conductive plastics in heat sink of vehicle LED headlamp.

Thermal Model Design and Analysis of High-Power LED Headlamp Cooling Device Based on the Thermoelectric Effect

In view of the characteristics of high-power light-emitting diodes (LEDs), such as strict junction temperature ( $T_{j})$ control, the enhanced cooling models based on the thermoelectric cooler (TEC) were presented to meet the thermal demand of high-power LED headlight. The cooling performance of different devices (air cooling and TEC, and liquid cooling and TEC) was evaluated and compared by measuring the LED case temperature. The details of the heat transfer performance, particularly, the startup performances of the TEC cooler as well as the influence of the fan rotate speed or liquid velocity on the system thermal performance, were obtained. It was found that the thermal performance had been elevated dramatically due to the reduction in hot-side temperature, and the TEC was more sensitive to the external fan speed or liquid velocity than purely air cooling or liquid cooling. In addition, the optimal current for air cooling and TEC was 3 and 5 A for liquid cooling + TEC. The investigations of the simulated ambient temperature on junction temperature, forward voltage, and output light were conducted. The results indicated that the case temperature changed linearly basically with the increase in heating power or the simulated ambient temperature. When the ambient temperature was within its severe level (60 °C–65 °C), the junction temperature could be calculated to 59.5 °C, and the corresponding output light was 1607.3 lm.

A light-emitting diode headlamp for motorcycles based on freeform micro-lenses

We propose a light-emitting diode headlamp for motorcycles based on freeform micro-lenses. The freeform micro-lenses include a collimator and micro-lens structures. The rays emitted by the light-emitting diode source are first collimated and then redistributed by the microstructures. We make a point by point relationship between the light-emitting diode source and the target plane according to Economic Commission for Europe Regulation R113 revision 2. Simulation results show that the light pattern of our proposed headlamp could satisfy the requirements of the regulation. Illuminance on the test points, lines, and zones can fully meet the Economic Commission for Europe Regulation. The optical efficiency of our proposed headlamp could reach up to 90%, which is much higher than the traditional design.

차량의 헤드램프 빔 패턴 인식을 위한 헤드램프 검사 시스템 개발

"Cut off line" in automotive passing beam has very important safety function because it serves for headlamp aiming. Headlights that are aimed incorrectly will not only perform poorly but also offend oncoming traffic. In addition, an objective definition of cut off line in low beam is necessary, since a requirement for correct aiming of the beams is specified within all the existing regulations. Accordingly, headlight regulations are requirements that automobiles must satisfy in order to be sold in a particular country. In this study, a more advanced recognition method for the cut off lines of the various headlamps commonly used in Europe, North America, and domestic is suggested and a headlamp testing system is developed to adjust the beam to the country-specific regulation. This system uses image processing technology to detect the cut off lines in the beam patterns of halogen headlamps, high-intensity discharge headlamps, and light-emitting diode headlamps as well.

The Design of High Power LED Headlamp

With the continuous development of LED(Light-Emitting Diode) manufacturing technology, the high power white LED is gradually applied in the field of all kinds of lighting .But with working time increasing of LED chips, their junctions temperature continue increasing, which lead to decrease light-emitting efficiency and reliability of LED chip, and even be failure. According to the serious heating of LED chip, this paper has been designed a fin-type aluminum radiator panels using Pro/E software. A LED constant current drive circuit is designed by using LTC3783 chip. With the ANSYS software, thermal analysis was carried out on the fin-type aluminum radiator panels, and eventually the mode of high power LED headlamps is determined. The stability of the LED constant current drive circuit is verified through experiments. The LED headlamps of 90W worked for ten hours, and the results of the experiments showed that the LED chip junctions temperature measured are less than 75°Cso we can solve heat dissipation of high power LED headlamps effectively.

Heat Dissipation Design of High Power LED Headlamp

High brightness white light emitting diodes(LEDs) are very promising in many new illumination applications. This paper is to investigate the cooling solutions of a LED heallamp. Air cooling with heat sink were proved to be unsuitable. A cooling method based on heat pipe is adopted which is proved to be effective. Simulations were performed with Flotherm software to investigate the thermal permance.A sample of LED headlamp is fabricated based on the structure of a certain sedan combined headlamp. The testing results are in accordance with the simulation results

High-illuminance Light-emitting Diode Headlamps for Medical Applications

High-illuminance Light-emitting Diode Headlamps for Medical Applications

Design method of high-efficient LED headlamp lens

Low optical efficiency of light-emitting diode (LED) based headlamp is one of the most important issues to obstruct applications of LEDs in headlamp. An effective high-efficient LED headlamp freeform lens design method is introduced in this paper. A low-beam lens and a high-beam lens for LED headlamp are designed according to this method. Monte Carlo ray tracing simulation results demonstrate that the LED headlamp with these two lenses can fully comply with the ECE regulation without any other lens or reflector. Moreover, optical efficiencies of both these two lenses are more than 88% in theory.

Performance evaluations of LED headlamps

Due to rapid progress in LED (Light Emitting Diode) technology, LEDs have become increasingly prevalent in applications to automotive lighting. This paper studies recent trends of LED headlamps along with various experiments regarding photometric characteristics, glare, and visibility. Experimental results are compared to those of halogen and HID (high intensity discharge) headlamps. LED headlamps are found to be still inferior to conventional headlamps with respect to glare. However, many properties of LED headlamps (luminous intensity, beam width, energy efficiency, and design) are competitive with halogen and HID headlamps. The findings in this investigation will henceforth be reported to the Korean Motor Vehicle Safety Standard (KMVSS).