LEDs are HOT right now!
We see them everywhere. Light emitting diodes, or LEDs, have found their way into hundreds of applications, from powerful flashlights to energy-efficient street lighting, and from automotive head lamps to long lasting, money saving lighting for homes and businesses.
Developed during the 1960s, original LED applications were limited to use in indicators and display panels. They were very easy to spot in many buildings’ exit signs. As the technology has grown, so have the number of applications.
How do they work?
LEDs are in the family of semiconductor devices, also called diodes. Computer chips, laser devices, and even photovoltaic solar cells are all semiconductors. Semiconductors allow current to flow only in one direction. By carefully engineering the materials and the design, these devices can be manufactured to serve many different functions.
A photovoltaic cell or photodiode is a semiconductor engineered to transform radiant electromagnetic energy into electricity. Interestingly, an LED does the exact opposite: it transforms electrical energy into light. In fact, if you study a diagram of the basic parts of each device, you’ll see that they both include a P-layer (a semiconductor with a positive character), and N-layer (a semiconductor with a negative character), and a P-N Junction (site where electron activity occurs between the p-layer and n-layer).
A cool experiment you can try:
Use an LED bulb to create electrical current, just like the PV cell on your calculator does!
What you need:
1 LED “grain of wheat” bulb (available from electronics stores)
1 set of alligator clips
A nice sunny place to experiment
The LED has two wire “legs”, the longer one is positive. Connect this longer leg to an alligator clip. Connect that alligator clip to the red (positive) lead from the VΩmA terminal of the micrometer. Connect the shorter leg to the remaining alligator clip. Connect this clip to the black (negative) lead from the COM terminal of the micrometer.
Set the micrometer to one of the DCA (Direct Current Amps) settings and aim the LED toward the sun until you get the highest reading. You’ll get the best readings at the 200μ or 2000μ (microamps) settings.
Your LED bulb should be creating electrical current!
Here’s what else is cool about LED lighting:
According to a report from the US Department of Energy, 74% of our general illumination needs will be met by LED lighting by 2030. In the year 2030, the energy savings from solid-state lighting will be approximately 190 terawatt-hours, or the equivalent annual electrical output of about 24 large power plants!
To download a PDF of the report, go to www.ssl.energy.gov/tech_reports.html.
Want to learn more about how LEDs and energy efficient lighting can save energy AND money? You can compare energy savings and costs of different lighting technologies with NEED’s Facts of Light and Comparing Light Bulbs activities. Check these out in our Monitoring and Mentoring Guide on pages 29 and 30.