Vitor C. Bender

Static and Dynamic Photoelectrothermal Modeling of LED Lamps Including Low-Frequency Current Ripple Effects

In this paper, a static and dynamic photoelectrothermal model including the impact of low-frequency current ripple on light-emitting diodes (LEDs) performance is proposed. The objective of this study is to evaluate the dynamical interaction among thermal, photometrical, and electrical properties of the LEDs when they are supplied by a dc constant current with a superposed low frequency sinusoidal ripple, which is the common case in offline LED drivers. Therefore, this paper presents both a model and experimental data for analyzing the LED photometrical behavior in terms of luminous flux, efficacy, flicker, and chromaticity. Three laboratory prototypes with different heat sinks and LED models have been tested. Experimental results are presented to evaluate the LED photometrical behavior under the aforementioned operating conditions and to validate the proposed modeling methodology.

Solid-State Lighting: A Concise Review of the State of the Art on LED and OLED Modeling

This article presents an overview of technologies for solid-state lighting (SSL). In recent years, light-emitting diodes (LEDs) have developed characteristics desirable for lighting applications. The success of these light sources for general lighting depends on the system design, which comprises an understanding of electrical and photometrical characteristics under the temperature effect on device performance. This review focuses on the main theoretical models for the characterization of SSL devices, regarding the electrical and thermal aspects to reach the desired photometrical characteristic for a lighting system. An approach about inorganic LEDs and organic LEDs (OLEDs) will be presented along with the application of these devices in SSL systems.

Design Methodology for Light-Emitting Diode Systems by Considering an Electrothermal Model

The knowledge about thermal, electrical, and photometrical characteristics of Light-Emitting Diodes (LEDs) is essential to achieve a good performance to the lighting system. This paper presents a methodology for designing LED systems. The main purpose is to provide an optimal operating point, considering the electrothermal design to achieve the maximum luminous flux for a given LED system. Based on two design routines, the proposed methodology brings the possibility to consider driver output current, heatsink size, and LED junction temperature in the system design. A mathematical analysis taking into account an LED electrothermal model is presented. Computational fluid dynamics simulation employing finite element method and experimental results validate the proposed methodology.

An optimized methodology for LED lighting systems designers

Understand thermal, electrical and optics characteristics of Light Emitting Diodes (LEDs) is essential to achieve a good performance to the lighting system. This paper presents an optimized methodology for designing LED lighting systems. The objective is to provide the designers an optimal operation point taking into account thermal, electric and optical LED system characteristics. The proposed methodology brings the possibility to consider driver output current, heatsink size and LED junction temperature in the system design. A mathematical analysis is presented and experimental results validate the proposed methodology.

Electrothermal feedback of a LED lighting system: Modeling and control

This paper presents the electrothermal modeling and control of a light emitting diodes (LEDs) system. The system consists on a Buck-Boost converter operating as the current driver and LEDs distributed along to the heatsink composing the luminaire. The model contemplates electric characteristics of the Buck-Boost converter and thermal characteristics of the luminaire. A control system is developed to regulate the LEDs current and to keep the adequate LEDs operating temperature. At the end, experimental results are presented for validation of the entire proposed system.

Study on the thermal performance of LED luminaire using Finite Element Method

Large LED (light-emitting diodes) clusters are currently designed to replace the commonly lamps used in parks, roadways, tunnels and street lighting. But the success of these designs is heavily dependent of the high performance of the thermal management. Thermal performance affects the light extraction, reliability and the lifetime of LED lamp. This paper proposes a solution to improve thermal design of LED luminaires. This solution uses a forced air convection into a closed cooling loop. Simulations employing Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) have been done to evaluate the system performance and to propose improvements in the airflow design. Comparisons of the experimental and simulation results are presented for validation.

Electrical characterization and modeling of Organic Light-Emitting Diodes (OLEDs)

This paper presents a new theoretical equivalent model (TEM) for Organic Light-Emitting Diodes (OLEDs). This TEM is useful to simulate and analyze OLED dedicated drivers, considering dynamic and steady-state operation conditions. A simple characterization procedure to OLED parameter identification is presented. Based on this procedure an OLED sample is used to validate the proposed modeling.

Modeling and Characterization of Organic Light-Emitting Diodes Including Capacitance Effect

This paper presents a new theoretical equivalent model (TEM) for organic light-emitting diodes (OLEDs). The parameters of TEM are identified using a simple characterization procedure based on auxiliary circuits and low-cost equipment. From this TEM, a method for intrinsic capacitance identification is proposed. This model is useful to simulate and analyze OLED devices considering dynamic and steady-state operation conditions. In addition, it provides guidelines for manufacturers and lighting designers to enhance the device performance and to design dedicated OLED drivers. In order to validate the proposal of this paper, four commercial OLEDs are tested, and the comparison between the theoretical and the experimental results is satisfactory.

Design methodology for street lighting luminaires based on a photometrical analysis

In this paper, an optical design method to solve the problem of illuminance distribution for LED street lighting luminaires is proposed. With this method, it is possible to calculate the amount of luminous flux required for a LED lamp, optimizing the uniformity of illuminance and luminance with use of lenses, in order to ensure the current national lighting standards for street lighting. As an example, a 75 W LED street lighting luminaire is analyzed. Simulations are performed and experimental results are used to show the agreements with standards requirements.

Indirect control of luminous flux and chromatic shift methodology applied to RGB LEDs

This paper presents a method of control for RGB LED systems, modelling and equating of a system of LEDs are shown in details in order to obtain constant output luminous flux information for each color, reducing the color shift with the temperature variation. Also the paper discusses the control strategy employed and the methodology employed to eliminate the temperature influence on the color shift. Some simulation results are shown in order to prove the methodology, followed by some practical results.