Desenvolupament d’una lluminària multicolor amb LEDs amb sistema de control intel·ligent

Abstract

The aim of this project is to develop a system able to reproduce the visible light emitted by a blackbody in a temperature between 1000 and 8000K using the LED technology. This light has an ideal color rendering index (CRI), so it can be used for any application. The traditional and obsolete incandescent light bulbs, acting as a blackbody radiator, offer a very poor efficiency converting the electricity into light, producing only 10-20lm/W. The developed smart system is controlled by an Arduino Nano equipped with an ATmega 328 microcontroller. It contains 6 different LED types: red, cyan, green, blue, warm white and neutral white. This selection of colors covers almost the whole visible band of the electromagnetic spectrum , allowing to fit the LED global light to the blackbody curve. The color temperature can be selected through two different graphical user interfaces (GUI) and they are programmed in MATLAB and App Inventor, a programming language for Android devices developed by the Massachussets Institute of Technology (MIT). On these interfaces the user can control the main parameters of the light, such as the color temperature and the global intensity. The intensity of the individual LED, the luminous efficacy and the CRI of each selection is given for informational purposes. Furthermore, the GUI developed in MATLAB shows a graphic with the color diagram and the planckian locus plotted inside, changing the position of a pointer for each color temperature selected. Moreover, the MATLAB GUI requires a USB connexion while the Android GUI needs the bluetooth technology. This microcontroller used can only provide 40mA of electrical intensity per pin. It causes several restrictions on the prototype, resulting in a low luminous flux (10-30lm) and a greater eficiency (30-50lm/W) than a halogen light bulb but smaller than a CFL. These issues can be solved changing the circuit, adding transistors and an external power source able to provide 700mA per pin, the nominal intensity of the used LED. This improvement increases the efficiency to values between 50 and 60lm/W, the typical performance of the CFL light bulb. Finally, the economical study shows that the cost of the prototype is approximately 180€, but an industrial process can reduce the price more than 130€, giving a final cost of less than 50€ per unit. This can be archieved due to the reduction of the connections board cost and the use of the microcontroller instead of the entire Arduino.