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LED knowledge

2015/4/25      view:

1What is LED?

LED stands for Light Emitting Diode, a kind of semiconductor which is used to give and receive the electronic signal into infrared rays or light, using the characteristics of compound semiconductor. This is used for household appliances, remote controller, electric bulletin board, various kinds of automation appliances.
Infrared LED Chip
Stands for IRED(Infrared Emitting Diode) Chip. The manufactured chip is used for IR Emitter, TV remote controller, optical switch, IR LAN, and for a module for wireless digital data communication.
Visible LED Chip
Stands for VLED (Visible Light Emitting Diode) Chip, whose color covers red, green and orange etc. This chip is assembled into lamp to be used for light source of indication or signal of various electric Products .

2Finding the Frequency from the Wavelength of Light

The frequency of light is related to the wavelength of light in a very simple way. The spectrometer can be used to examine the light from the LED, and to estimate the peak wavelength of the light emitted by the LED. But we prefer to have the frequency of the peak intensity of the light emitted by the LED. The wavelength is related to the frequency of light by , where c is the speed of light (3 x 108 m/s) andis the wavelength of light read from the spectrometer (in units of nanometers or 10-9 meters). Suppose you observed the red LED through the spectrometer, and found that the LED emits a range in colors with maximum intensity corresponding to a wavelength as read from the spectrometer of= 660 nm or 660 x 10-9 m. The corresponding frequency at which the red LED emits most of its light isor 4.55 x 1014 Hertz. The unit for one cycle of a wave each second (cycle per second) is a Hertz.

3Finding the Energy from the Voltage

Suppose you measured the voltage across the leads of an LED, and you wished to find the corresponding energy required to light the LED. Let us say that you have a red LED, and the voltage measured between the leads of is 1.71 Volts. So the Energy required to light the LED is E = qV or E = -1.6 x 10-19 (1.71) Joule, since a Coulomb-Volt is a Joule. Multiplication of these numbers then gives E = 2.74 x 10-19 Joule.

4How Much Energy Does an LED Emit?

The electric energy is proportional to the voltage needed to cause electrons to flow across the p-n junction. The different colored LED''s emit predominantly light of a single color. The energy (E) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression: E = qV Joules. This expression simply says that the voltage is proportional to the electric energy, and is a general statement which applies to any circuit, as well as to LED''s. The constant q is the electric charge of a single electron, -1.6 x 10-19 Coulomb.

5What Causes the LED to Emit Light and What Determines the Color of the Light?

When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions. In the p region there are many more positive than negative charges. In the n region the electrons are more numerous than the positive electric charges. When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region. Once in the p region the electrons are immediately attracted to the positive charges due to the mutual Coulomb forces of attraction between opposite electric charges. When an electron moves sufficiently close to a positive charge in the p region, the two charges "re-combine".

Each time an electron recombines with a positive charge, electric potential energy is converted into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material (usually a combination of the chemical elements gallium, arsenic and phosphorus). Only photons in a very narrow frequency range can be emitted by any material. LED''s that emit different colors are made of different semi-conductor materials, and require different energies to light them.