MadSci Network: Physics

Re: How is it possible to have White LED's in flashlig

Date: Wed Nov 3 14:17:49 2004
Posted By: Kenneth Beck, Senior Research Scientist, Chemistry and Physics of Complex Systems, Pacific Northwest National Laboratory
Area of science: Physics
ID: 1099425492.Ph

Dear Bill,

Here are short answers to your questions, followed by an extremely 
informative link to LED theory, design, and manufacture.

(1) One technique used to produce white LEDs is by using a blue LED 
epoxied into a cup-shaped reflector with a phosphor-containing dye (such 
as Coumarin 6, used in dye lasers).  The blue LED emits light.  The dye, 
in turn, is stimulated by the blue light through a charge-transfer 
reaction and emits a broad spectrum of color.  Together, these are 
preferentially designed to "mimic" the appearance of white light by the 
human eye.

(2) Yes, when they become affordable.  Right now, a white light LED 
equivalent to a 30 Watt bulb costs ~$160/each.

(3) The electricity-to-light conversion efficiency is reported as high as 
98-99%.  This means almost zero heat production.

(4) Yes, here it is...


This summarizes much of the work done by Professor E. Fred Shubert of 
Rensselaer Polytechnic Institute in Troy, NY.  It's a fantastic website 
for all things LED!

Good Luck!

---* Dr. Ken Beck

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