What is LED
A light-emitting diode is a semiconductor light source that emits light when an electric current is passed through it. Electrons in the semiconductor recombine with electron holes, emit energy in the form of photons
Inside the LED
LEDs are containing of compound semiconductor materials. Therefore, LEDs are made up of elements from group III and group V of the periodic table. However, Examples of III-V materials commonly used to make LEDs are gallium phosphide (GaP). Similarly, gallium arsenide (GaAs).
How led works
Light Emitting Diode (LED) works only in forward bias condition. So, When Light Emitting Diode (LED) is forward biased, the free electrons from n-side and the holes from p-side are force towards the junction.
When there is a jump over of electrons at the p-n junction, the electron loses a portion of its energy. In regular diodes this energy loss is in the form of heat. However, in LEDs the specific type of N and P conductors produce photons (light) instead of heat
How LED emits light?
The energy level of free electrons in the conduction band is high compared to the energy level of valence electrons or holes in the valence band. Therefore, free electrons in the conduction band need to lose energy in order to recombine with the holes in the valence band.
The free electrons in the conduction band do not stay for long period. After a short period, the free electrons lose energy in the form of light and recombine with the holes in the valence band. Each recombination of charge carrier will emit some light energy.
Forward and reverse bias
In this simple battery-lamp circuit, the diode will either allow or stop current through the lamp, depending on the polarity of the applied voltage.
In this first figure Current flow is permitted. So, the diode is forward biased. However, In the second figure Current flow is prohibited. So, the diode is reversed biased. However, The direction of the diode symbol’s “arrowhead” points at the direction of the current in conventional flow.
When the polarity of the battery is such that current can flow through the diode, the diode is said to be Circuit is Forward-biased. Similarly, when the battery is “backward” and the diode blocks current, the diode is said to be Reverse-biased. Moreover, Diode act like a switch: “closed” when forward-biased and “open” when reverse-biased.
Types of led
High-Power LEDs
An LED with a power rating greater than or equal to 1 watt is called a high-power LED. This is because other LEDs have a power rating of less than 1 watt. However, High Power LEDs are very bright and they are frequently used in Flashlights, Mobile torch, Spotlights, etc.
RGB LED (Red-Blue-Green LED)
RGB LED means red, blue and green LEDs. However, RGB LEDs products combine these three colors to produce over 16 million hues of light. It contains 3 LEDs on a single chip and this LED is controlled by a technique called PWM (Pulse Width Modulation) With the help or microcontroller/Arduino we can control the output of the RGB LED to produce a wide range of colors.
Bi-color LEDs
The Bi-color LED is a handy little component that allows two colors (red and green) in a single LED while only having two pins (cathode and anode). Moreover, depending on the configuration of the leads, the color will be activated, in the above figure: if the positive voltage is applied to the Green LED then the green LED lights (ON). Likewise, if the positive voltage is applied to the Red LED then the Red LED lights (ON). However, with two terminal system only one LED lights at a time.
Tri-color LEDs
In the three terminal LED system; LED grounding the cathode (-) commonly if the positive voltage is applied to the Green LED then the green LED lights (ON). Likewise, if the positive voltage is applied to the Red LED then the Red LED lights (ON). However, Because the two positive wire connected separately it is possible to lights up the 2 LEDs at a time.
Infrared LEDs
These types of LEDs are also called as IREDs Infra-Red Emitting Diodes. The infrared band can be divided into Near Infrared (NIR) and Far Infrared (IR). Far infrared does not come in the range of LEDs. NIR can be further divided into two bands, longwave and shortwave NIR.
Ultraviolet LEDs
Ultraviolet (UV) light is an invisible form of electromagnetic energy (light energy) that travels at a higher frequency and carries more energy than visible light. However, Ultraviolet UV-B causes sunburns, UV-C is dangerous as it kills things. Moreover, it is advisable not to stare into an ultraviolet LED.
Caution
- LEDs Emit very strong UV Radiation during operation
- Do not look directly in to the UV LED its harm your eyes
- Keep out of reach of childred
Application
- UV lighting is an excellent tool for air and water purification
- Used to Check UV watermarks to validate currency
- Identifying bodily fluids in forensic crime scenes
Name Symbol Wavelength Range Ultraviolet A UV-A 400 – 315 nm Ultraviolet B UV-B 315 – 280 nm Ultraviolet C UV-C 280 – 100 nm
SMD LEDs (Surface Mount LEDs)
SMD means surface mounted diode. This is a better technology than the first-generation DIP LEDs. The SMD type LEDs are mounted on an aluminum substrate and covered with an epoxy resin. However, SMD LEDs are usually differentiated based on their physical dimensions. For example, the most common SMD LEDs are 3528 and 5050.
Simple LED Circuit
Here is the Circuit Diagram for simple LED circuit. For building this circuit You just need to connect positive terminal of LED with the one end of resistor and then connect another end of resistor with the positive terminal of Battery. Likewise, connect the negative terminal of LED with the negative terminal of Battery. This Negative Terminal of Battery is also referred as the Ground.
What happens if we connect the LED in reverse direction? Well, when there’s no current-flow, there’s no light. However, A reversed LED nothing happens, its bock the current flow. So, it will not work properly.
What is the advantage of LED Lights?
- LED Lights are Eco Friendly.
- Long Life
- Less consumption of Electricity
- No Chemicals use in LED Lights
- LED Make by Solid Material with no filament and tube or Bulb
- No Need of warm up Period. LED LED’s light instantly in nanoseconds
- LED Lights can used as Directionally Lights.
- LED Lights are not affected by cold temperatures
Applications of LED
- LED TV
- Automotive Lighting
- Traffic Signals
- Mobile torch light
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