Light emitting diode (LED)

Light emitting diode (LED)

Light emitting diode

A diode that converts an electrical signal into light energy so that energy can be efficiently emitted without producing heat. 

Light Emitting Diode (LED)

LED (Light Emitting Diode) is a special diode that emits when a current is applied to the junction of a semiconductor. In addition to visible light, there are also diodes that emit invisible ultraviolet rays and infrared rays. It can be said that it is a low-power, long-life and highly efficient lamp (miniature bulb), and it is playing an active role as an alternative to lamps and fluorescent lamps for energy saving. To go back in history, the development of blue LEDs in 1993 and pure green in 1995 led to the development of red, which had already been developed, and full-color displays. At present, light emitting diodes (LEDs) are blending into everyday life by changing the TV, audio equipment, remote control, Blu-ray disc and various other forms on a daily basis. In the next few years, miniature bulbs and fluorescent lamps may stop producing, and the shadows they see may disappear.

Photodiode (phototransistor)

A diode that converts light energy into an electrical signal as opposed to an LED. A current is extracted and used according to the light irradiation amount on the PN junction of the semiconductor.

Image sensor

Extract light energy as an image.

Solar power

Extracts light energy as electric power.

Photo coupler

An optical coupling device that integrates an LED that converts an input electrical signal into an optical signal and a photodiode that converts the optical signal into an electrical signal.

Photo-interrupter

A device that detects an object between light receiving elements by blocking light.

Optical communication device

For high-speed communication centered on optical fiber, for optical communication, laser diode for optical communication and light receiving element for optical communication

Principle of LED

When a voltage is applied to the LED (structure is a PN junction semiconductor) from the forward direction, holes move from the P region and electrons move from the N region toward the PN junction region. When electrons and holes come near the PN junction, a phenomenon called recombination occurs in which they stick to each other and disappear. The total energy after this recombination is smaller than the energy that electrons and holes had individually, so that energy is emitted as light. This is the LED emission phenomenon. The emission color (wavelength of light) varies depending on the LED semiconductor material and impurities added, and ranges from the ultraviolet region to the visible light region and infrared region.

	Led	Incandescent light bulb
Shades of light	Single specific color such as red / green / blue	Since various wavelengths (light) are mixed, it is close to white
Heat generation	Few	Large amount (more than 80% of energy becomes heat)
Lifespan	Long (20 times more than a light bulb)	short
power consumption	Few (about 1/10 of light bulb)	Many
Response time	Very small (less than 1 million of light bulb)	Large

Light emitting diode structure

Light emitting diode chip was formed on the cathode electrode

Light emitting diode structure

Light emitting diode lighting circuit

An example of a basic circuit that lights a light emitting diode. LED current limiting resistors are connected in series, and batteries are connected to both ends.

Light emitting diode lighting circuit

PN junction

This is due to natural fermentation that is emitted when holes that are injected from the P-type region to the N-type region or electrons that are injected from the N-type region to the P-type region recombine.

Energy gap

When the electrons in the conduction band recombine with the valence band, a direct transition occurs, at which time light corresponding to the energy gap is emitted.