About LEDs

Light Emitting Diode

LED stands for Light Emitting Diode.

They are various types of LEDs; the standard model is a long, two-pin version.

SMD (Surface Mount Device) LEDs are flat, and so are more easily mounted on flat surfaces for a variety of applications.

High power LEDs (usually SMD) are rated at a minimum of 0.5W; some models reach up to 100W, with a corresponding increase in brightness.

LED Composition

LEDs are semiconductor light sources, meaning that they are made with a semiconducting material.

LEDs have two pins; one is called an anode, and one is called a cathode. The anode is the longer pin, and carries a positive charge. The cathode is the shorter pin, and carries a negative charge.

Current flows in through the anode and out through the cathode, lighting the semiconducting material along its way.

Each anode and cathode pin is connected to the diode, which is encased in a transparent plastic lens. The lens is solid and protective, earning LEDs a “solid-state” reputation of durability and longevity.

LED-Diagram
Photo Credit: Lighting Research Center

In some cases, the lens is be tinted to indicate the light color, but it is not the tinting that colors the light.

The first LEDs emitted a red light, and it was many years before other colors of LED lights could be created.

Various materials are added to the diode/junction point of the LEDs to change the colors. The materials also affect the voltage of LEDs.

Alloys such as aluminum gallium indium phosphide (AlGaInP or AlInGaP) are used to create red/yellow/orange LEDs, which have a forward voltage of approximately 2V.

Alloys such as gallium nitride (GaN) are used to create blue (as well as true green and some white) LEDs, which have a voltage of approximately 3.3V.

White LEDs can also be created by combining red, green and blue light, or by using a blue LED with a yellow and/or orange phosphor coating.

History of LEDs

In 1907, it was discovered that inorganic materials can light up when electric current it applied.

In the late 1940s, with the progression of transistor development, new details about light emission “came to light“.

The first actual LED was developed in 1962. It produced a very weak red light.

By the 1970s, LEDs were commonly used as indicator lights in a variety of devices, and during the 1980s their brightness and stability only continued to improve.

In 1993 the blue LED light was developed, closely followed by green and white colors.

LED brightness and heat-efficiency continued to improve in the years that followed.

Now, LEDs are a safe, reliable source of lighting poised to take over from traditional light sources.

Additional LED Facts

The benefits of LED lighting are well-documented.

The equivalent wattage comparison chart is also useful information.