288 Dipti Chitnis1 Full length

Main aim of this paper is to present the information regarding the present lighting system and to explain how solid-state lighting (SSL) can stimulate the development of the science and technology and how electricity can be saved with this energy saving, energy efficient green technology. Various methods to generate white light, advantages and key challenges are outlined in this paper. Thus if we succeed in overcoming all these key challenges, we can lighten up our lives with eco friendly and energy efficient OLEDs with the green technology called Solid State Lighting. INTRODUCTION: LIGHTING UP LIVES WITH ECO-FRIENDLY AND ENERGY EFFICIENT OLEDs FOR SOLID STATE LIGHTING 1 2 3 DIPTI CHITNIS ,N. THEJO KALYANI , S.J. DHOBLE Department of Applied Physics, Shri Datta Meghe Polytechnic, Nagpur, India Department of Applied Physics, Priyadarshini College of Engineering, Nagpur, India Department of Physics, RTM Nagpur University, Nagpur, India BIONANO FRONTIER VOL. 5 (2 II) NOV. 2012 ISSN 0974-0678 346 Solid state lighting is the alternative lighting achieved by a new technology, where illumination is obtained through semiconductor devices. It has the potential to far exceed the energy efficiencies of incandescent and fluorescent lighting. Lighting applications that use light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or light-emitting polymers(LEDPs) are commonly referred to solid-state lighting. It has the potential to revolutionize the lighting industry, opening a gate way to change the way we light the world. This technology holds promise for lower energy consumption and reduced maintenance. Cutting-edge research now shows a bright future for solid-state lighting as the next generation of light sources for general illumination, from homes to commercial applications. Hence a lot of research is going on in developing the ecofriendly materials for emission of light in the required region of visible spectrum. History of Lighting : After the discovery of th electromagnetism and electric current in early 19 century, many scientists attempted to devise a simple and affordable home lighting. The outcome of efforts made by many scientists led to the invention of incandescent light bulb, this will remain as one of the greatest inventions of mankind. The early invented lights even didn't illuminate a room and the life time was even less than 15 hrs. The credit for developing the first long lasting filament goes to Edison and in 1979 he finally succeeded in making a bulb carbon filament, which burnt brightly for 600 hrs at its first trail. Later, scientists tried to improve the filament until they found that tungsten filaments outlasted all the types. These long lasting lamps became immensely popular and were soon installed in billions of homes across the world. Incandescent light bulb :Incandescence is the phenomena in which emission of light takes place from a material when heated to higher temperatures. They have low efficiency because over 90% of the energy is emitted as invisible infrared light or heat. Electric lamps are by far the most common source of light used on Earth, other than our sun [1]. Halogen Lamp: It is an improved version of Incandescent light bulb. Instead of Tungsten filament and argon gas, it has small amount of Iodine or Bromine, which enables the lamp to work at high temperatures. They have better operational life time and luminosity as compared with incandescent lamps. They are used in automobiles, head lamps, floodlights etc. In an Incandescent light bulb electricity is allowed to flow through a metallic filament connected between two contacts. Tungsten (Tg) is the mostly used filament as it is having very high melting point. The filament gets heated by the electrical energy and it glows to give light. This filament is enclosed in a glass bulb, filled with inert gas Argon (Ag), which ensures its glow without burning. Life time of these bulbs usually lie in the range of 1000 to 5000 hrs. In incandescent light bulb only 10% of light produced is in the visible (VIS) region. Almost 90% of the power consumed is emitted in the form of heat. Hence shift towards a more energy efficient electric lamp, which led to the development of fluorescent lamps and Light Emitting Diodes (LED's). Fluorescent lamps : These lamps contain mercury and coating of phosphors. Application of electricity excites mercury, producing Ultra Violet (UV) light. This light is absorbed by the phosphors coating and changes this UV light to VIS light. There are efficiency losses in generating the ultraviolet light, and in converting the ultraviolet light into visible light. Later came the Compact Fluorescent lamp (CFL), which is the smaller version of fluorescent lamp, built to fit into standard house hold light sockets. CFLs are highly efficient with improved life time; hence incandescent lamps are replaced by CFLs. Light Emitting Diodes(LEDs) :LEDs have greater significance in the contest of need for electrical energy conversion and pollution control worldwide. These devices convert electricity into light energy when current flows through them. They are made of semiconducting materials, namely p-type and n-type, which form p-n junction when placed in contact with each other. The material considered for the formation of the junction determines the color of light emission. In LEDs 80% of energy is consumed and the remaining 20% is dissipated in the form of heat. They have good life time around 5000 hrs, so ideal for long running operations. Thus, their life time last up to 10 times longer than a standard light bulb or CFLs. They are brighter, energy efficient, available in broad range of brilliant colours, safer, cheaper, they are nontoxic. They are point sources; they are not suitable for larger displays, hence shift towards the next generation displays called organic displays. Organic Light Emitting Diode (OLEDs) : Organic materialbased electroluminescent (EL) devices have excellent