Oh, the lowly light-emitting diode or LED. For years we have seen LEDs used in everything from indicator lights on electronic devices to "taillights" on sneakers. Until recently, the light output from an LED was too low to be considered for practical uses such as replacing the ubiquitous incandescent bulb.
LED designs share much in common with semiconductor manufacturing. The constant gains in computer processing power are a good analogy to the increasing light output seen in modern LEDs. These low-cost, energy efficient devices have tremendous potential to do far more than just inform us if a device is turned on or not.
LED 101
LEDs are diodes at heart. A diode restricts the flow of current to one direction: Electricity enters from one side and exits out the other. In between, the current passes through a structure called a die. The die contains an area called the junction, where the actual light generation takes place. A contact in the center of the junction is attached to the incoming lead (the anode). As current passes through the LED, the materials that make up the junction react and light is emitted. By experimenting with different junction materials and package designs, LEDs are now bright enough to be considered for applications that traditionally use incandescent bulbs.
Current LED designs are at least five times more efficient than their incandescent counterparts. Besides producing little heat and being energy-efficient, LEDs are solid-state devices with no moving parts. This makes LED lighting systems very reliable and gives them an operating life in excess of 10,000 hours.
The white-light challenge
The current challenge facing LED manufacturers is to produce white light. Initially, designers tried mixing red, blue, and green LEDs into a single array with the combined result achieving the desired white. While this arrangement can work, slight variations among LEDs of the same color means that each array must be tuned individually to achieve just the right shade of white.
LED manufacturer
LumiLeds visited TechTV Labs recently to show off its latest designs. We discussed the challenge of designing white LEDs and how manufacturers were doing it. Two interesting designs involve using phosphors similar to the coatings on the inside of a television tube. One LumiLeds design combines an ultraviolet LED and an RGB phosphor to produce the desired white light. The other design used a blue LED and a yellowish phosphor to generate white light.
One drawback to current white LED designs is the amount of light produced. The brightest white LEDs made today offer about 20 lumens compared to the 55 lumens that red-orange LEDs are able to produce. For reference, one
lumen is equal to the amount of light emitted within a specified conical-shaped angle called a steradian.
LumiLeds recently introduced a new packaging technology that increases the brightness and reliability of their LEDs. Named Luxeon, these LEDs represent their brightest designs yet. LumiLeds claims its Luxeon LEDs currently average 23 lumens each and will reach 50 to 100 lumens by 2002. The small shape and low heat generated by such LEDs will enable home and industrial lighting systems to take on shapes and sizes never before possible.
Energy sipping solutions
You may have noticed that many cities have begun to replace traffic signals with LED-based designs -- significant energy savings being a key reason. Consumer-orientated products are beginning to appear as well.
A company named
Tektite offers an array of LED-based products, including some rather impressive flashlights. Using an array of multiple LEDs, Tektite's offerings can compete against standard incandescent designs while providing improved battery life and ruggedness. Tektite provided us with a prototype of its upcoming Trek 6000 EX60 LED flashlight. This $300 monster packs an incredible 60 white LEDs into its pistol-shaped design. All of Tektite's LED flashlights are designed primarily for underwater use and feature depth ratings from 300 to 1,000 feet.
Streamlight is another company specializing in portable LED lighting solutions. TechTV Labs tried out their $22
Stylus brand LED-based penlights. Waterproof and constructed from anodized aircraft-quality aluminum, the single-bulb Stylus offers simple operation and a non-slip grip. Streamlight claims the LED used in their Stylus line will last in excess of 100,000 hours -- over 11 years. Streamlight offers the Stylus in three casing colors with an assortment of LED color options to choose from.
For an interesting look at the history of LEDs and related products, point your browser to a site called
For The Love of LEDs. Webmaster Craig Johnson packed his site with LED related information and links. Mr. Johnson also provides some hands-on testing experience in a great section titled "The Punishment Zone".
Outlook
LEDs have found their way into other applications as well. The automotive industry sees LED arrays as an excellent replacement for taillights and sidelights on cars. Having a taillight that responds faster than an incandescent bulb and will likely never need replacing is a win-win situation for consumers.
The Nasdaq sign in New York City is one of the most impressive uses of LEDs ever crafted. Using an array of 18 million red, blue, and green LEDs that function as pixels, this monster can mimic a television screen capable of displaying stunning graphics and video.
The power savings offered by modern LED lighting systems should be reason enough to consider them over incandescent designs. The semiconductor-style manufacturing techniques used in LED production provides plenty of room for improvements and experimentation with different materials. While we are reaching the practical limits of Thomas Edison's dream, LEDs will continue to follow their own Moore's Law by doubling their brightness every 18 to 24 months, as they have for the last 30 years.
