Although visible light communication (VLC) systems provide high density links for use in Internet-of-Things (IoT) devices, the design of high rate VLC transmitters that maintain luminaire efficacy is an open problem. In this article, a novel approach to the integration of VLC within light-emitting diode (LED) drivers is proposed through the replacement of freewheeling/blocking diodes with light-emitting devices termed a light-emitting commutating diodes (LECDs). In this manner, communications and illumination can be provided using a simple, cost effective design while employing no additional components. The subtle change of LED driver control signals facilitates the transmission of data from LECDs while simultaneously supporting illumination functions. Lighting controls such as dimming are maintained and combined with modulation through the use of overlapping pulse position modulation (OPPM) and performance is quantified. Prototype buck and boost converters with LECDs are implemented and their efficacy is measured. Though current commercial LEDs are not intended for such signalling applications, we experimentally demonstrate their feasibility in this application and suggest methods to make such converters reliable. It is demonstrated that the addition of an LECD improves the efficacy of the luminaire as compared to conventional LED drivers while simultaneously enabling a VLC downlink.

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Light-Emitting Commutating Diodes for Optical Wireless Communications Within LED Drivers

With the advances in the technology of materials based on GaN, high brightness white light emitting diodes (LEDs) have flourished over the past few years and have shown to be very promising in many new illumination applications such as outdoor illumination, task and decorative lighting as well as aircraft and automobile illuminations. The objective of this paper is to investigate an active liquid cooling solution of such LEDs in an application of automotive headlights. The thermal design from device to board to system level has been carried out in this research. Air cooling and passive liquid cooling methods are investigated and excluded as unsuitable, and therefore an active liquid cooling solution is selected. Several configurations of the active liquid cooling system are studied and optimisation work has been carried out to find an optimum thermal performance.

https://hal.archives-ouvertes.fr/hal-00171358/document

Liquid Cooling of Bright LEDs for Automotive Applications

Despite precautions taken by the operators of maintenance vehicles, insufficient visibility of winter operations vehicles causes many collisions in the United States. Numerous methods have been developed to enhance the visibility of winter operations vehicles. Although these methods have improved the visibility of winter operations vehicles, information regarding the current state of practice of these methods is crucial for the safety of winter operations vehicles, and commuters. For safer winter operations, it is critical to investigate the differences, similarities, and challenges associated with the existing methods for enhancing the visibility of winter operations. This research examines the differences, similarities, and challenges associated with these methods using a survey to collect information from state transportation agencies. Questionnaire distribution included all 50 states to investigate patterns among the states and 25 Texas Dept. of Transportation (TxDOT) districts to gather the state of practice of the operations vehicles’ visibility methods. Results of the survey brought forward the inefficiencies of some current visibility methods. For example, rear airfoils were reported to be ineffective, while many state DOTs use and maintain the airfoils despite the inefficiencies. Although a wide range of dissimilarities was found in the use of message signs and retroreflective markings, they are reported to be inexpensive and effective. It is expected that the findings of this study help transportation agencies implement more effective methods for enhancing the visibility of winter operations vehicles. 

Visibility of Winter Operations Vehicles: The State of Practice in the United States

Surveying the Effectiveness of Methods for Enhancing the Visibility of Snowplows in Texas

Abstract In this study, an experimental study based on the target visibility criteria is carried out for dark and foggy environments, where only vehicle headlights are active. More specifically, the performances of the headlights containing halogen, xenon, and LED light sources in dark and foggy weather conditions are examined and the performance of each headlight is evaluated separately. According to the general result of the visibility experiments, the participants perceived the target object in a shorter time when halogen headlights are used. It is also observed that the average target perceived times of the participant under foggy conditions are at different levels depending on the type of headlights with different correlated color temperature (CCT) and color rendering (CRI) indexes. According to the experimental results performed under foggy conditions, the target detection times of the participants are the shortest at the halogen headlight, the second at the xenon headlight, and the third under the LED lights. It has also been observed that this sequencing is gender-independent. However, the ratio of the detection time of female participants to that of male participants varies between 1.72 and 3.65 times. In other words, female participants perceive the targets in a much longer period than male participants. 

/pdf/performance-investigation-of-different-headlights-used-in-se9v2vdk.pdf

Performance investigation of different headlights used in vehicles under foggy conditions

The improved benefits of the general light emitting diode (LED) attracts the automotive lighting industry and as a result many of the higher end cars today are fitted with LED headlight in place of halogen and xenon bulb based headlights. The advantages include higher operating efficiency, compactness and improved bulb life. In this research, a comparison between the halogen and LED based headlight systems was carried out by focusing on their temperature distributions and light intensity illumination. For this purpose, headlights of SUMO Victa, a Multi Utility Vehicle (MUV) from TATA Motors is used. A LED bulb assembly was fabricated using SMD LEDs which was retrofitted into the Victa headlamps by replacing the original halogen bulb. To dissipate the heat produced by LED, a heatsink fabricated from copper sheet and fitted with copper powder was used. LED bulbs are fitted around the heatsink to effectively remove the heat generated during LED operation and control the junction temperature. To evaluate the performance of the fabricated SMD LED bulb and halogen bulb, experiments were carried out to capture the temperature distribution on bulb, inner and outer surface of headlight along with light intensity. The results clearly show that the LED bulb achieves higher light intensity, less power consumption and temperature distribution than a halogen bulb.

C. RameshKumar

Papers

Investigation on light intensity and temperature distribution of Automotive's Halogen and LED headlight