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The Revolution in Light Emitting Diodes (LED)






Light Emitting Diodes (LED) have historically been most commonly used as state indicators, for example, as a "Power On" indicator.  The light output from the LED was low, but the advantages for the designer were that the LED energy efficiency was terrific, was capable of "instant on" operation, and that the reliability and lifetime were very good.  Another advantage is that an LED contains no hazardous materials like mercury. 


The outlook for LED use is improving.  There has been much advancement in LED technology in the last few years, allowing new applications.  The manufacturing cost of LEDs has been relatively expensive because the process used a sapphire substrate. Researchers at Purdue University have developed a process for replacing the sapphire with inexpensive silicon.  Currently, a 30-watt LED bulb can cost about $30, but this should change. 






Another reason for the changing outlook is the need for energy efficiency.  A law passed in 2007 requires all light bulbs to become more energy efficient. Over a three-year period, starting in 2012, new bulbs will have to use 25 percent less energy, for the same light output, as incandescent bulbs. Currently, the only light technology in widespread use that meets that standard are compact fluorescents, which use 70 percent less energy.   Today, compact fluorescents account for less than 20% of total bulb sales. With a more efficient light source, the energy is saved in two areas.  The lamp uses less electricity, and less energy has to be spent cooling the HDTV lamp module, and air conditioning your home.


An interesting example of a new LED application is cities replacing their incandescent traffic lights with LED arrays.  This is happening because the electricity costs can be reduced by 80%, and the maintenance costs are also reduced.  Let’s assume that a traffic light uses 100 watt bulbs. The light is on 24 hours a day, so it uses about 2.4 kilowatt-hours per day. If we assume power costs 8 cents per kilowatt-hour, it means that one traffic signal costs about 20 cents a day to operate, or about $75 per year. If we assume eight signals per intersection, that's about $600 per year in power per intersection.  An LED array should consume less than 20 watts (instead of 100), so the power consumption drops by a factor of 5, to less than $120 per intersection.  For a city with many intersections, that can add up.


Another application is the use as a light source in High Definition Televisions (HDTV).  The LED is being used as both a backlight in LED HDTV systems, and as a projector light in rear projection HDTV systems, including the DLP HDTV systems.  A good example of an LCD system is the Samsung "Series 9" LCD HDTV that uses LED backlighting with local dimming technology.  Local dimming allows for very high contrast ratios.  Samsung projects that by 2010, more than 30% of all LCD HDTV sets will utilize LED backlighting instead of the fluorescent bulbs currently used.  The first LED lamp DLP system was the Samsung HL-S5679W, introduced in 2006, which also eliminated the use of the color wheel.


With fluorescent lighting in a HDTV, the lamps need to be replaced every few years.  The replacement can cost about $200, and there's also the hassle of scheduling maintenance.  The equivalent LED bulb should last more than 10X longer.  In practical terms, the LED should last the lifetime of the overall system. 


LED is a new, old technology that is changing our world for the better.









 About the Author:


Brian Bradshaw is an InfoComm Certified Technical Specialist (CTS), Microsoft Certified Technology Specialist (MCTS), and CompTIA A+ Computer Technologist.  Areas of expertise include Video, HDTV, Audio, Computation, SATCOM Systems, and Communications.

Website:  http://bradshaw-vacuum-technology.com/