This section:
http://www.allaboutcircuits.com/vol_3/chpt_3/12.html
This chapter:
The chapter mentions it, but I can't help feeling that some distinction should be made between older models and new LEDs, since the physics between them is slightly different. LEDs are a hard one to keep up with, as the field is currently (still) in a constant state of flux, but the differences between the older, dimmer LEDs are pretty profound (lower voltage drop, differences in physical construction, slightly different physics,among other things). The newer LEDs use internal mirrors (I'm not sure of the exact arrangement) to boost efficiencies.
http://www.allaboutcircuits.com/vol_3/chpt_3/12.html
This chapter:
Yellow LEDs were developed about the same time as red and green. They can also be created with red/green bidirectional LEDs, but they are also a stand alone color, a very old one at that.Diodes made from a combination of the elements gallium, arsenic, and phosphorus (called gallium-arsenide-phosphide) glow bright red, and are some of the most common LEDs manufactured. By altering the chemical constituency of the PN junction, different colors may be obtained. Some of the currently available colors other than red are green, blue, and infra-red (invisible light at a frequency lower than red). Other colors may be obtained by combining two or more primary-color (red, green, and blue) LEDs together in the same package, sharing the same optical lens. For instance, a yellow LED may be made by merging a red LED with a green LED.
The chapter mentions it, but I can't help feeling that some distinction should be made between older models and new LEDs, since the physics between them is slightly different. LEDs are a hard one to keep up with, as the field is currently (still) in a constant state of flux, but the differences between the older, dimmer LEDs are pretty profound (lower voltage drop, differences in physical construction, slightly different physics,among other things). The newer LEDs use internal mirrors (I'm not sure of the exact arrangement) to boost efficiencies.
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