The light emitting diode (LED) comes in a wide variety of sizes, shapes, and colors, and is something every ham should be familiar with.  There are a number of exam questions related to LEDs.

LEDs are more common than you may realize.  Not only used on ham radio equipment, they are typically found on most electronic gadgets, primarily as indicator lights, most often as power or status indicators.

Developed in the early 1960s, visible LEDs became practical replacements for miniature incandescent lamps in the 1980s.  Their main advantage is in efficiency (wasting little power), but they also last many years and illuminate instantly, all compared to incandescent light bulbs.

The above question phased out of the General class exam pool in 2019 but it speaks to the benefits of LEDs over other technology.  This example from the Tech license exam pool shows an LED being used in a traditional power supply circuit as a power indicator:

Useful as more than just on/off indicators, LEDs, when grouped, really open up interesting applications.  When formed as bars in a figure 8 arrangement, the classic seven segment display is created:

This revolutionized electronics to display numbers quickly and inexpensively and were an early use of the technology starting in the 1970s.

Also, when different color LEDs are bunched together their combined light can form a different color, often to achieve white.  This is the principle of LED back lighting for flat panel displays and for the recent adoption for home and general lighting (replacing light bulbs).

White LEDs (or a blend of other colors to make white) weren’t practical until the mid-1990s, and it took years to become economical.  The widespread use of LEDs for display back lighting and general lighting is now less than 15 years old.

For those interested in the technology, we’ll dive into some of the details of LEDs now.  As the name implies, an LED is a form of diode, the simplest possible semiconductor device formed by Continue reading →