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WLED: cool, clear, white light at home
IMAGINE saving 95 per cent of your electricity bill for lighting. This is now possible with a new kind of bulb based on solid-state lighting. Unlike a filament bulb that wastes 95 per cent of the input energy in heat, the new solid state bulb only wastes 5 per cent; the remaining 95 per cent goes into producing light. You can start beginning to save energy soon, but there is a catch. You have to read this article and do it all yourself!
This article starts with a brief history leading to the use of solid state lighting (SSL) techniques for home and commercial use. It describes how you can make these semiconductor-based lights at home, and save enormously on the electricity bills.
The development of semiconductor based white light is largely attributed to Shuji Nakamura, a scientist working in the Research and Development department of Nichia Chemical Industries, Japan. Nakamura was obsessed with achieving semiconductor laser light in the 390-450 nanometers (nm) range, which appears blue to the human eye. After many years of research and experiments, Nakamura finally developed the blue LED (Light Emitting Diode) and the first blue lasers. This crucial breakthrough led to the emergence of White LEDs.
LEDs at one point were small, dull, pinpoints of light, barely noticeable. However, these new White LEDs are far from dull. In fact, their light is so bright that it is being used in numerous applications these days, from cars, to cellular phone displays, to the large billboards such as one can see in New York’s Times Square. Apart from high energy efficiency, they offer high reliability, high durability and a lifetime of about 100,000 hours. That’s well over 11 years of continuous usage!
So how, one might ask, can one use this information? Has anyone tried these lights at home? The answer is: yes. There is already a house in Defence Society, Karachi, that is using white LEDs on its gate to light up its vicinity. After reading the following guidelines, you too can rig up something similar in your home.
First, here’s what you need to make a simple, cool, WLED lamp:
— 40 small white LEDs (5mm). These are now easily available in electronic markets in our major cities. (cost Rs5 each)
— A small perforated copper board (commonly known as a “vera-board”) (Rs15)
— Some regular copper wire (Rs5)
— A 12 V DC adaptor, with a rating of about 300mA (Rs50)
— The use of a soldering iron and solder wire.
All this and, of course, some basic initiative and know-how of putting a simple circuit together!
First decide on the LED arrangement on the copper board. A simple and easy configuration is 10 columns of four LEDs each in series (strung in a line). Note that the diagram above shows only one such string. You will need to put nine other strings in parallel to this one. Of course, you can use more or less strings to make a brighter or weaker lamp.
The key is to get a 3V potential difference across each LED, and a recommended 20mA of current going through each column. Make sure you correctly identify the positive and negative terminals of each LED! The longer leg is the positive terminal (anode) and the shorter one is the negative (cathode).
Once you know the arrangement you want, take the copper board, and solder the LEDs onto the board (this is the fun part). Carefully connect the adaptor to your board using the copper wire. Make sure you tape any loose wire or open connections with insulation tape. Plug in your adaptor to a power outlet. Voila! You have light!
The above procedure is a simple way of putting together White LEDs to build an efficient, long lasting light source. Based on your knowledge, you could adapt this basic circuit to suit your requirements.
The above light (using 40 LEDs) uses a total of about 2.4 Watts, and yet gives the light output of almost a 40 Watt filament bulb! It further has a much longer life, and does not generate unnecessary heat. You could always experiment with the placement of these LEDs on the vera-board to get suitable light for your application.
For all those intimidated by the idea of using a soldering iron, these wonder lights are not out of reach. There are rumours of a company bringing White LED bulbs to our market that you can directly plug into a socket to enjoy solid-state lighting. Easy, albeit not as exciting as making your own. These wonder bulbs are already available in North America, but their cost is still too high to be affordable in our market.
White LEDs are not only a solution to energy efficient lighting, but also a way of providing light to the estimated 2 billion people without light in the developing world. The small power usage by these LEDs makes them perfectly usable with solar panels and other alternate energy sources. Already projects like “Light up the world”
It is estimated that by the year 2020, about 50 per cent of the lights in the world will be replaced by solid state lights. Let’s hope Pakistan is quick to realize the potential of this technology, and be one of the first to implement it on a wide scale.
The author is an Electrical Engineer, working at Comstech’s new Center for Innovative Technologies, Islamabad
