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For Exploration 4C you should read one set of material. Be prepared to discuss and answer the questions in the next section in small groups, using this material and your knowledge of blackbody emission and semiconductor band gap transitions.

Agilent HP Application Notes, Briefs, and Press Releases

A.	HP Application Brief 004: Reliability of Precision Optical Performance AlInGaP LED Lamps in Traffic Signals and Variable Message Signs (10 pages, 4/97, original reference: http://ftp.agilent.com/pub/semiconductor/led_lamps/abi004.pdf ). HP Press Release (September 30, 1997): New High-flux-output AlInGaP Emitters Offer Industry's Best Value Point in LED Light Output (original reference: http://www.semiconductor.agilent.com/news/pr/30sept97.html) HP Press Release (October 11, 1999): HP Supplies SnapLED Automotive-lighting Assembly for 2000 Cadillac Deville. First U.S. Automobile with All-LED Taillights (original reference: http://www.semiconductor.agilent.com/news/pr/11oct99.html or http://www.lumileds.com/auto_lighting/ledtaillights.html ).
B.	HP Application Note 1155-3: LED Stop Lamps Help Reduce the Number and Severity of Automobile Accidents (8 pages, 11/98, original reference http://ftp.agilent.com/pub/semiconductor/led_lamps/an1155-3.pdf or http://www.lumileds.com/auto_lighting/pdf/3733.an11553.pdf ). HP Application Note 1176: "Advantage of SnapLED 150 LED Product Compared to other Lighting Technologies in Automotive Signal Lamps" (4 pages, 7/99, original reference: http://ftp.agilent.com/pub/semiconductor/led_lamps/an1176.pdf or http://www.lumileds.com/auto_lighting/pdf/an1176.pdf ). HP Press Release (February 26, 1996): New HP LEDs To Replace Incandescents In Automotive Taillamps (original reference: http://www.semiconductor.agilent.com/news/pr/26feb96.html).
C.	HP Application Note 1155-2: Electrical Power Consumption Savings with LED Signal Lights (16 pages, 11/98, original reference: http://ftp.agilent.com/pub/semiconductor/led_lamps/an1155-2.pdf or http://www.lumileds.com/auto_lighting/pdf/an1155-2.pdf ). HP Press Release (November 19, 1997): HP SnapLED Automotive Lighting Assembly Featured in 1998 Ford Explorer (original reference: http://www.semiconductor.agilent.com/news/pr/19nov97.html).
D.	HP Application Note 1155-1: Warranty Cost Savings of LED Signal Lights (16 pages, 11/98, original reference: http://ftp.agilent.com/pub/semiconductor/led_lamps/an1155-1.pdf or http://www.lumileds.com/auto_lighting/pdf/an1155-1.pdf ). HP Press Release (May 18, 1998): HP Introduces "Traffic-signal Green" LEDs, Becomes First "All Color" LED Supplier for Traffic-Signal OEMs (original reference: http://www.semiconductor.agilent.com/news/pr/18may98.html).

Group Activity

In groups of people who have read different material (ideally one A, B, C, and D member), discuss and formulate written answers to these questions comparing light bulbs and LEDs. Submit one set of answers per group.

1. Which lights faster? In what applications does this make a difference? In what ways are the differences significant?
2. Which has a longer life expectancy? In what applications does this make a difference? In what ways are the differences significant?
3. Which uses energy more efficiently? In what applications does this make a difference? In what ways are the differences significant?
4. Does any vehicle that you use regularly (car, truck, van, or bus) have LED brake lights? Are there any LED traffic lights in your town? How can you tell? Name several ways to distinguish between light bulbs and LEDs.
5. Which looks redder? (If LED lights are not available in your area, see the Module Tools CD.)
6. Which costs less? Consider purchase price, maintenance, and operating costs.
7. Why are LED brake lights more important on large trucks than on cars?
8. What things cause bulb or LED failure?
9. How does operating temperature affect bulb or LED life expectancy?

Other References

"LEDs: From Indicators to Illuminators," Andrew Bierman, Lighting Research Center, Rensselaer Polytechnic Institute, 1998. http://www.lrc.rpi.edu/Ltgtrans/led/leds.htm

"Optimizing the Design and Use of Light-Emitting Diodes for Visually Critical Applications in Transportation and Architecture," John Bullough, Kun Michelle Huang and Kathryn Conway, Lighting Research Center, Rensselaer Polytechnic Institute, 1998. http://www.lrc.rpi.edu/Ltgtrans/led/led-contents.html

"Changing the World of Lighting, All Things Considered", National Public Radio, July 15, 1998. NPR's Ivan Amato reports on the new enthusiasm for light-emitting diodes in everything from buses to floor lighting in theaters. Created in a crystal, light from an LED is sharper and comes on faster, making it popular for tail-lights; the Washington D.C. Metro subway system is installing them now. Engineers say LED will probably replace the incandescent lights indoors and out, and save energy as well.